(scroll down the page to the 9th post for the downloadable/printable version..)
ok folks
There are many posts asking about re-spraying and how to do it..
I have put this guide together today (blurry vision now)
and will add pictures etc to it .
I have covered a section on how to fix paint chips and small rust bubbles
and a big guide on everythign from stripping a car, to dent repairs, metal preperation, etch priming, priming, sanding, guide coats, painting laquering etc etc
hope you find it useful
let me know of any obvious mistakes or ask about any bits missed and I will try add them
Also attached it in a word 2002 document for you to download and print..
AND NO NICKING IT TO USE FOR COURSEWORK..!! 
Rust bubble and Chip fix Guide 3
Fixing paint chips/small rust bubbles 3
A way to repair the chips quickly and economically 3
A Better Way 3
Applying Paint 4
Finishing 5
Now a complete respray of a whole car or a panel 6
Assess the paint condition on the car 6
How Deep? 6
What you will need 6
Cellulose or 2 pack/2k 7
Prep Tips 7
Before you begin 8
Paint Removal Choices 8
Sandblasting 9
Media Blasting 9
Chemical Removal 9
Hand Stripping 10
Power Sanding 10
Metal Conditioning 10
Removing dents/straightening the panels 11
Priming and Block Sanding 11
Surface Cleanliness 12
Masking 12
Primers 13
Sanding 15
Block-Sanding 15
Getting ready to paint 16
Compressors & Guns 16
Paint Safely 17
Choosing Your Paint 17
Putting the paint on 18
Spray Gun Patterns: 19
Fixing Problems 20
What the heck is that ? 21
Introduction
I have decided to sit and create this guide for my fellow TMF users.
I am covering a guide to fix paint chips and small rust bubbles, and also a complete guide for prepping and re-spraying a complete car.
Rust bubble and Chip fix Guide
Fixing paint chips/small rust bubbles.
The most common problem we face with our minis is rust. This method is a guide to fixing very small rust bubbles and paint chips. I will cover panels later
Whilst assembling a 300SL I had restored as a show car, I accidentally put a few small chips in the new paint. After the car was completely assembled and finished, this was repaired by sanding the damaged area, applying primer, block-sanding it, and spot-painting a section of the panel, trying to keep the repair as small as possible. Matching the colour might have required painting the whole panel, which was time-consuming and expensive.
A way to repair the chips quickly and economically
Brush-touching the chips with a dab of paint. You might think the paint would look as if it had been brushed, but I will describe the process of building up the paint just above the original level then gently sanding it down.
I you follow the guide unless you knew exactly where the chip was, you could never see the repair. The process works best with solid colours; metallic colours may come out a little blotchy but still easier than a complete re-spray of a panel
A Better Way
First, get the right touch-up paint for your car. For a recent model with original factory paint, a paint retailer such as Halfords can sell you a small bottle of touch-up paint with an integral brush. You paint code is normally 3 letters and located on the VIN plate on the inner wing under the bonnet.
If you don't know the name of the colour, if it has faded, or if the car has been repainted, your local automotive paint store can match a paint sample.
Your car has a code used to determine the formula for mixing the colour.
Clean the chipped area before painting. Use a product called panel wipe, it costs about £10 for 5 litres. Paint will not stick to a surface with wax, grease, or silicone on it.
Use a sponge or soft rag to clean the area around the chip, especially the chip itself. Clean off any accumulated residue. Let it dry. If you see bare metal, dry it immediately to prevent rusting. If you see surface rust buy a fibreglass pencil from Maplins and clean it, they are about £3.
This works well for a small chip, perhaps caused by a stone, but a long scratch takes more skill and patience; it can be repaired, but rarely.
Practice on a small, out of-the-way area so that if you make a mistake, it will be hidden. This process is not recommended for a car with a lot of chips. If that's the case, consider repainting the panel. For one or two chips, this alternative saves the difficulty and expense of spot-painting a larger area or repainting an entire panel.
If you spot-paint an entire area and blend new into existing paint, you have two dissimilar paints: the new paint and the original underneath. When you spot-paint an area then finish it, you might get an exact colour match then, but in time the two paints applied at different times age differently, and a ring or spot will appear.
Applying Paint
With the area clean and dry, you'll need a good brush with a very fine point. A large brush will slop paint over the edge of the chip. To keep the paint inside the chip, you need a very small brush with just a few bristles.
Mix the paint thoroughly. Liquid paint settles as it stands so mix in all the pigment at the bottom of the container, or the colour will be off. If the paint is too thick to go on the brush and be applied in a light coat, it will need to be reduced to a thinner consistency. If you're using lacquer, you'll need lacquer thinner; if you are using an acrylic enamel, use acrylic reducer. To get the desired consistency, paint should be thinned approximately one part thinner to one part paint or one half thinner to one part paint.
With the brush, build successive light layers of paint into the chip. Paint shrinks as it dries, so build the layers gradually. If you put one big glob of paint into the chip, it will continue to dry for months, shrinking as it does so. Even if you finish it flat, a few months later a crater will develop where the repair was made. Allow drying time of at least an hour or two between paint layers. The longer you wait, the better the finish you'll get, so let the paint dry thoroughly. Two to four layers of paint will be needed to fill the crater. Because the paint will shrink, build the final layers a little above the crater surface.
It should be fairly close but slightly above the surrounding paint. Let this dry for several weeks. In the meantime, your car won't look awful. It will look like you simply brush-touched that area, which will certainly look better than the chip. The key to this entire process is that the paint must dry thoroughly.
Finishing
Learning the skill of finishing is another key to success. You'll need a cube about an inch square that is perfectly flat on at least one side to use as a small wet sanding block.
If you don't have something flat of this size, cut a block of hardwood or a piece of dowel. Before sanding, you might mask off the area by putting tape about an inch away all the way around. Then if you get a little aggressive in your sanding, you won't sand and scuff the surrounding area.
Use 1,000-grit or 1,200 grit ultra fine wet and dry sandpaper. You need very little; a sheet will cost about a pound at an automotive paint store. Tear off a tiny square, enough to wrap around the block, and then use a sponge to wet the area as you sand. Use the sandpaper and block to level the paint mound down to the surrounding original paint.
Use the lightest possible pressure on the block, and gently wear down the little mound. Sand a little and very lightly—this can take mere seconds—then dry the area and inspect it. When you see that the mound has disappeared, you've gone far enough.
Avoid sanding too much. If the paint is old or thin, or if you sand too hard, you'll go right through the finish. If you very carefully let the block float with just the gentlest pressure over the little mound of paint built up over the chip, you'll wear off the top of the new surface without removing much if any of the surrounding paint. Ideally, you'll scuff it just a bit.
Next, use a cutting/rubbing compound, available at most automotive stores.
Use a soft cloth in the area scuffed by the sandpaper, and rub until the scratches are gone. Rubbing in one direction works best. After polishing, wipe the area dry and inspect it. If you see deeper scratches, do a little more polishing with the compound polish.
Finally, wipe the surface clean and use wax or automotive polish to finish the area around the chip. Done right, you've filled the chip and finished the top so that it blends in nicely. If you look very closely, you may see the spot. If you notice bubbles trapped in the paint (they produce white specks in the centre of the chip) your paint was probably too dry, too thick. As you grow more skilful in applying wetter, thinner layers, the surface will not bubble.
This method can effectively repair a chip without painting an entire panel. I've used it on show cars, where it even held up to the scrutiny of judges.
Now a complete respray of a whole car or a panel…
Whether amateur or pro, few collector-car restorers paint their own vehicles. Paint is so important to the overall visual impact of the car that it's usually better left to the pros.
I will try to de-mystify the painting process and provide you with knowledge that will prove useful whether you decide to attempt paint work yourself or hire a professional
I will try to show you the proper way to prepare a car for a show-quality paint job, detailing the materials used and providing some hints on how the pros do such a good job.
Assess the paint condition on the car
Your first step is to analyse the condition of your car's painted surface.
Dull finishes can often be restored to brilliance with polishes and waxes. (See my guide on getting that shine). At least clean your car and take a good look at it.
Problems such as flaking, cracking, crazing, peeling, and pinholes are easy to spot but can't be fixed without removing the old finish. If your car has already been painted several times, strip off the old finishes and start from bare metal.
How Deep?
After a complete examination, if you mini has several layers of paint I recommended stripping the surface to the metal to remove all contaminants in the old paints. It's a lot of handwork, but this ensures against the old paint surfacing through the new materials. Chemicals used in older paints can linger in trace amounts. Going to the metal also allows you to fix dings and dents by working the metal itself, not via body filler. Another reason to remove all the paint is to regain sharp body lines and edges that several layers of re-spray have rounded off.
If the car still has original paint and is excellent condition only strip sections that need repaired.
What you will need
Most automotive paint manufacturers have colour-matching tables and computers that quickly match old colours to today's new high-tech paints. Consult the manufacturer one-on-one for each exact painting situation because conditions are never the same from car to car—let the experts call the match.
Numerous prep chemicals and materials will be used in the painting process. We'll need a low-volatile metal cleaner. It's used on bare metal surfaces to remove any oils or other contamination just prior to priming the area. (Panel Wipe)
Coated-abrasive 24-grit sanding discs are used to grind out any body fillers or other materials found on the metal surface. When used with a 5-inch grinder or dual-action
(D-A) sander, they save hours of hand-sanding.
Stopper with catalyst is used to fill small surface imperfections and dings. This putty is a skin-filler only and can't take the place of filler for large repairs.
A non-sanding, self-etching primer will be used with a hardener on bare metal to etch into the surface for a secure.
Rust-preventative bond (POR 15 Metal ready)
A working primer that is used over the surface of the self-etching primer to finish the bodywork and to ready it for the final block-sanding. You don't need to sand the self-etching primer before applying the working primer.
Outlawed paints.
As of 2007 2 pack or 2k paints will become outlawed because of the contaminants it releases into the atmosphere.
The paint legislation has imposed strict regulations on paint manufacturers and body shops to comply with restrictions.
Each body shop is required to record the amount of materials used each day in a logbook. The book is periodically checked by authorities and, if the shop doesn't stay in compliance, serious sanctions and fines can be levied against the owner. Therefore, it's in everyone's best interest to be concerned with air quality, particularly since you can get a fabulous finish with today's paint technology while remaining within clean-air standards.
Cellulose or 2 pack/2k
Two-stage/ 2 pack (or basecoat/clearcoat products are used as excellent in terms of durability. These paints are tougher than cellulose and produce outstanding and long-lasting results. This system gives an almost bullet-proof surface that will shine for years with a little care, where as Cellulose will require polishing approx twice a year to maintain that deep shine.
Prep Tips
Here are a few tips for the beginner who needs to be a part of the process as well as for the stubborn do-it-yourself-er who wants to save every penny. I hope these hints will save you time, money, and cursing.
TIP 1: One of the main things to remember is the importance of physical protection during the job. Particle masks are cheap insurance for your lungs while sanding, rubber gloves will protect against chemical absorption through the skin, and a respirator and disposable paint suit will protect you while spraying the primer.
With the exception of fiberglass-bodied cars, the make, size, or model of the vehicle makes no difference—the preparation of the body and application of products is the same for a car, truck or lawnmower.
TIP 3: While doing bodywork on a vehicle with a vinyl roof or convertible top, always completely seal these areas with masking paper before starting. Fine sanding dust and primer overspray can ruin the surface of your top. A few minutes of precaution can save big money later.
TIP 4: If you're working with body filler that needs to be shaped, try a "cheese grater." This is a small file that looks like a regular kitchen cheese grater, and it makes short work of cutting hard filler for preliminary shaping.
TIP 5: Whenever working around tyres and wheel wells, use a plastic bin bag over the tyre to prevent overspray on the rubber. Overspray is a pain to clean off, and a black bag will easily fit over the mini tyre and wheel.
TIP 6: After you think you've found all the little dings in the paint, apply a dusting "guide coat" of black paint over the primer then block-sand the area. Any small indentations will retain the black dusting and immediately show up.
TIP 7: It is best to stick to one paint manufacturer. I can't stress enough how bad it is to cross brands as although rare, you can have all sorts of issues.
Before you begin
Prior to starting any bodywork, you can save money by stripping all the exterior trim from the car. All front-end trim, door handles, wheel well trim, and other bright work have been removed and can be detailed at home while the car is in the body shop
Paint Removal Choices
How do you remove old paint, primers, and fillers? Several methods include sandblasting, media blasting, chemical removers (hot tanks), hand stripping, power sanding, and grinding.
Sandblasting is a quick, effective, and economical way to strip a painted metal surface. Sandblasted metal also provides an excellent surface for adherence of primers and fillers.
Still, sandblasting has significant negative aspects. To avoid distorting and stretching the metal, an operator must be thoroughly experienced with sheet metal. I restored a 1955 car that, in a previous body shop, had its boot lid sandblasted. It took me days to shrink the stretched areas back to the correct contours. Another snag with sandblasting is work hardening of the sheet metal surface. Sand grains hitting sheet metal have the same effect as striking the panel with thousands of tiny hammers, making the panel stiffer.
In my opinion, sandblasting is unacceptable when a car is still assembled because sand and dust migrate to every part of the car, getting into bearings and mechanical components as well as every nook and cranny. Years later you'll still see sand fall out of hidden crevices. Sand grit quickly destroys machined surfaces such as bearings and bushings. Even if the parts are masked and sealed, grit will get in.
Sandblasting is good for removing rust and paint from heavy metal parts such as castings and housings. It works great on things like bumper brackets or a totally stripped chassis. Due to the possibility of panel warpage, it should never be used on aluminium.
Media Blasting
Removing paint by media blasting is increasingly popular. It's similar to sandblasting with an important exception. Instead of sand, it uses another media—hard plastic crushed to the consistency of sand. The same material used for common plastic buttons, it is hard enough to remove paint and primers yet has no effect on the metal surface beneath. I saw a demonstration on a die-cast metal part that had been chrome-plated then partially painted. Although the chrome was unprotected, the media blast removed the paint without damaging the surface. With this method you'll still have dust everywhere on an assembled car, but you won't have sand grit to damage mechanical parts.
The main drawback is that this process removes paint but does not remove anything more than loose rust. The media isn't hard enough to dry out rust. I have used this method and the media did an excellent job without affecting the metal underneath.
Still, surface rust in the lower panels and wheel housings had to be removed with a small grinder and wire brushes - very time consuming. Media blasting is also not very good at removing plastic body fillers, which are best removed by a grinder. Media blasting is somewhat more expensive than sandblasting due to the higher cost of the media.
Chemical Removal
There are several methods of chemical paint removal. Hot tank stripping, or dipping, is an efficient way to strip bodies and parts. Dipping involves immersing the body or part in a tank of hot caustic solution. The body is submerged for several hours until paint and undercoating have softened enough that they can be washed off with a strong stream of water. The body is returned clean and de-rusted (the caustic also attacks rust, effectively removing it), ready to be washed with a metal conditioner (POR 15 Metal Ready) and primed.
Hand Stripping
Another option involving chemicals is hand stripping. A chemical paint remover, bought in gallon cans, is brushed in liquid paste form onto a painted surface. The paste is allowed to work a few minutes, then a scraper or putty knife is used to remove the softened paint and undercoating. Several applications are usually necessary to take off al1 the paint.
Occasionally the bottom primer coats seem little affected by the stripper and must be removed by sanding or grinding. Hand stripping is a nasty business. The fumes are noxious, and the chemicals can burn unprotected skin. Because it removes paint without damaging the panel, hand stripping works well, but it is less advantageous where there is a lot of paint or filler on the panel. The stripper is expensive and can require numerous applications.
Power Sanding
Our final methods use sandpaper or grinding discs. A high-speed grinder with 16 or 24 grit grinding discs will quickly remove paint and fillers and rust. Unfortunately it removes metal, too. If you are not careful, deep scratches and gouges can occur. Sometimes excess heat caused by friction can warp a panel.
Grinding is best for removing small areas of paint that haven't responded to other methods. Use care when grinding near chrome or glass; a grinder throws off sharp hot particles at high speeds that can pit unprotected areas.
Power sanding is a paint removal method with few drawbacks. Dual action (DA) sanders combine orbital and random motions, quickly grinding away paint without the rough action and heat of a body grinder. Relatively soft paint may gum or load up DA sandpaper quickly, but stripping with DA is appropriate on any painted surface. It is only limited by where the DA can reach with its round, flat disc. Probably the cheapest and safest method if you attempt the stripping yourself, it requires only a DA sander and minimal skill.
Metal Conditioning
After a surface has been completely stripped of paint, primer, and plastic fillers, the next step is metal conditioning. On bare metal, rust forms quickly. It is important to clean off this surface rust and be sure the surface is chemically clean. To etch the surface for better paint adhesion, use metal conditioner. I use POR 15 Metal ready, it cleans light surface rust and leaves a zinc coat on the metal surface. The metal should then be sprayed with a light coat of primer to prevent rust. Improper use of metal conditioner can cause paint failure later. Primer is porous so will not prevent rust in wet/damp conditions.
Removing dents/straightening the panels
To get to dent on the mini is generally not a big deal, you can get to the back of most panels and using a body panel beating kit from machine mart (£20) you can generally use the various hammers and dollys to straighten up most surfaces.
For areas you can not get to the back of you use a tool called a sliding hammer, this involves drilling a small hole and threading in an attachment, then attaching the bar with the weight on it and sliding it outwards, when the weight hits the end of the bar it pulls the dent. Treat this original process gently—use the drift to get as close to the original contour as possible. Then apply the minimum possible amount of filler, essentially just to smooth over the straightened metal.
To eliminate any high spots, gently tap the area with a flat-head body hammer. This will bring the metal into a surface conformity (shop slang for "as smooth as possible") prior to adding the body filler or Filler
A light coat of sanding primer is applied over the filler only and allowed to dry. Any pinholes or imperfections in the filler will now appear and can be filled with cellulose putty (this sinks as it dries) or a stopper such as top stop (like a thin filler). After any remaining repairs are made and each individual area is sanded smooth, a coat of the working primer is applied over that area. This protects the bare metal from moisture while you work on other portions of the car.
Priming and Block Sanding
Having looked at various paint removal methods by now we've stripped the old finish to bare metal—or we have an original finish where the paint is adhering with no failure problems such as cracking, chalking, or pinholes. In both cases, the process of preparing the surface for paint is similar. Your goal, through a process of gradual refinement, is to create a surface as perfectly smooth and as free from flaws as possible.
Surface Cleanliness
You will use a medium stopper (thin filler) to fill and build up the flawed surface, then you'll block-sand it to level out this primed surface. First, let's discuss a very important requirement before priming: a clean surface. If the surface is bare metal, then a metal conditioner such as panel wipe will clean it, physically and chemically.
Promoting adhesion through cleanliness and following the paint manufacturer's instructions during each step of the process is extremely important. If that beautiful paint job you've spent so much effort to create doesn't stick to the metal underneath, you'll have to strip it off and start over.
A painted surface must first be thoroughly cleaned with a wax and grease remover. Modern waxes contain silicone, which must be removed before new paint can be applied. Nothing sticks to silicone. Another way to clean existing paint that also etches it is to scrub the old paint with Scotch Brite and Ajax powder (the kitchen cleaning stuff). Be careful to avoid scratching glass and chrome if you use this method. After the finish is thoroughly clean, the next step is to repair the chips and scratches. Remember, the new finish will only mirror the surface to which it is applied. Ninety percent of paint work is preparation. The actual spraying of the colour coats is a minor part.
Broken areas such as chips and scratches should be feather-edged, i.e., the chips must be sanded smooth and gradually tapered back to the surrounding level so that you feel no edge. This can be done easily using a sanding machine such as a Dual Action sander. Start with an 80-grit disc to work the rough edges down, then finish with 220. Existing paint should also be sanded with a 220-grit dry or 360-grit wet to remove any evidence of gloss. Thoroughly clean the surface, paying particular attention to nooks and crannies where paint dust or sludge may accumulate.
Finally, wash the entire surface with wax and grease remover (Panel wipe). After the surface has been cleaned and prepared for painting, be careful not to touch it with hands or gloves or in any other manner. Check the surface for smoothness by rubbing your hands over it before the final cleaning. Even after washing, your hands always have a certain amount of oil on them, which is sufficient to destroy the durability, adherence, and appearance of your new finish.
Masking
Before spraying any primer or paint, cover and protect adjacent areas from overspray. Areas to be protected should be covered with masking paper held to the body by masking tape. Good quality masking paper and tape will permit no paint to penetrate or seep through to the panel, chrome, or glass it is protecting. Tape must adhere easily to painted surfaces, chrome, glass, or stainless steel. Equally important, no adhesive must remain on the surface after the tape is removed.
Years ago I had the misfortune of using some inexpensive tape. To make things worse, the tape stayed on the car for several weeks. I ended up removing it with lacquer thinner, steel wool, and a safety razor blade. The inferior tape adhesive stuck to the chrome, rubber, and glass and literally had to be scraped off. As I recall, this took me several days. Believe me, a roll of 3M tape is cheaper than several days of labour.
Primers
Even new sheet metal panels have grinder gouges and stamping flaws that make the surface less than perfect. The typical paint job, only a few thousands of an inch thick, will only accentuate flaws. Primers and high build primers are designed to fill these imperfections.
Primers are relatively thin under coatings whose primary function is to promote adhesion between bare metal and subsequent coatings. Their secondary function is to prevent rust. Aluminium and zinc-coated panels require special primers for proper adhesion. (Etch primers) Although primers provide excellent adhesion and rust protection, they are relatively thin-bodied and have poor filling or building characteristics.
A primed panel can be sanded in as little as one hour after priming
Drying time is extremely important. I've found it best to give stopper/filler plenty of drying time. All surfaces have some shrinkage as they continue to harden or dry. Sanded too soon, they continue shrinking, causing small flaws or distortions in the final painted surface. Whenever I do a show-type paint job, I let the primer dry for up to several weeks before sanding, depending on weather conditions.
Inspect each panel and then sand the previously repaired areas clean of primer. They need to be readied for a full coat of self-etching primer.
Once all the panels are smooth and clean, it's time to apply the non-sanding metal-etching primer. The preparation for this step may not make sense right off, so bear with us. First, hit the metal surface with 80-grit paper on the sander to apply a good texture for the primer to grab.
The area is now wiped down with metal prep and blown dry to remove any particles left by the grinding process. Whenever dealing with metal or grinding debris, wear nose and eye protection.
Thoroughly scrub the area with a slightly damp cloth this remove any oil spray and leftover residue from the grinder and your hands. Take particular care in small detail areas like the lock holes and dry as you go along. (Hairdryer is good here)
Before cleaning the bare metal with surface prep (use one called "Panel Wipe"), carefully read the instructions on the bottle. All of the products should come with complete instructions printed on the container. A bathing coat of surface prep is applied with a clean, soft cloth and wiped until dry. This is the final treatment prior to squirting on the self-etching primer.
Each work area is masked off individually if the surrounding areas have not yet been prepared for the self-etch primer so that the primer won't chew into unprepared metal. Be thorough and exacting while masking off the car—loose spray will get through wherever it can
A metal mixing stick is an indispensable tool for mixing today's paints. Incorrect amounts of material can lead to disastrous results: paint that doesn't dry falls off or hardens prematurely in the gun.
For 2 pack This mix is two parts primer, one part hardener. When the hardener is added, the marker should show material to the 3-.
For cellulose it is generally 50/50 mix of paint and cellulose thinners (Varies with temperature) the paint should flow of the end of the stick like pouring cream
The primer is applied with a low-pressure/high-volume gravity-feed spray gun. Light and even passes are the best, allowing 10 minutes between coats for the prior to set up. Three coats are usually sufficient to completely cover the metal
The primer lays down smooth, has a nice workable sheen and seals the surface from moisture.
A dusting of black paint, called the guide coat, is applied over the entire surface of the car. Use a very light spray. It's called the "lie detector" because a light sanding will leave definitive black trace paint where the metal is deformed.
Standing flat with an 80-grit paper long board will find any low spots in the metal. The dusting coat will remain in the low areas while they grey primer will surface through the guide coat. This indicates areas that you will need to fill or lower using the panel hammers.
Several light coats of primer are applied over the repaired area, and the rest of the car is now cleaned and sanded clear of the guide coat. The repaired area will be sanded again once any other damage is fixed. The whole car is now sanded, and other areas that need attention are detected
To get really smooth panels a sanding block will not do. For this you need a sanding board, basically a long sander, you can make this out of a piece of straight timber, the longer the better as used with the guide coat it will let you see high and low spots on the bodywork
Sanding
Block-Sanding
After the primer is dry is dry, it is block sanded, then more filler/stopper (top stop) is applied. Depending upon the degree of perfection desired, this process can be repeated three to six times.
Block-sanding is a process where sandpaper is used with a hard rubber sanding block. I make my own blocks out of such things as balsa wood and rubber hose to conform to the surface being sanded—flat, gradual curve, compound curve, etc. Sandpaper backed by a sanding block gradually wears down the high areas.
A guide coat of contrasting colour primer or paint is sprayed over the primer before sanding begins. As sanding continues, the guide coat is sanded off the high spots and left in low areas, providing a guide to sanding and identifying areas requiring additional filling. More top stop (thin filler/stopper) is applied over these low areas, and the blocking process is repeated.
Cellulose putty has about the same consistency as the familiar glazer's putty but has an entirely different composition. It is usually made of the same basic material as the primer but is heavier in solids. Gouges or scratches left after the blocking process can be filled with spot putty.
The typical priming and block sanding process would involve:
1. several "blockings" with 100-grit, aluminium oxide, open-coat, dry sandpaper and a long-board sanding block
2. blocking with 150-grit dry followed by a blocking with 220 wet and a hard rubber block
3. final priming and block-sanding would be done with 400 wet and a soft rubber block
Use blocks for all sanding. Bare hands don't provide enough support to level the primer surface evenly and can even create ripples in the final finish. Generally, use the longest block possible; using a short block doesn't show up the low spots.
Determining whether or not a panel is truly smooth is easy after the final paint is on, when reflections show up every minor undulation, but you can detect them while block sanding. First, the contrasting guide coat will remain in low spots, so you know where you have to sand or fill. Second, your hands can feel unevenness; put your dry palm on the metal, and move it sideways as well as back and forth. Thin fabric work gloves may help. When you're almost finished block-sanding / clean off the sanding dust and dampen the panel with a damp (not wet) rag. Sight down the panel under the right lighting, and you'll see reflections in the damp sheen
Hopefully this brings us to the point where we are ready to begin painting.
We'll look at the various types of paint and go over the painting process, from application of sealers to spraying the colour and finally, colour sanding and final finishing.
Getting ready to paint
The first step, before we spray the colour coats, is to again thoroughly clean the surface. Contaminants can hinder adhesion and create other problems later. Wax and grease remover will again be used, with plenty of clean rags, to clean the surface. If more than a few days have passed since final sanding, the surface should again be lightly sanded with a 360 or 400-grit wet sandpaper (or finer, for metallic paint) to "open up" the primer for maximum adhesion. Paint adheres best to a recently sanded surface.
After the wet-sanding residue is carefully cleaned off, and all nooks and crannies are blown out with compressed air and thoroughly dried, Clean the surface down with panel wipe, apply it and immediately use a 2nd dry cloth to clean it off.
The surface is then wiped with a tack rag, a cheese cloth impregnated with a sticky wax-like substance. Lint or dust sticks to the tack rag and is removed from the primed surface as you wipe.
Compressors & Guns
Compressed air is used throughout the painting process — to apply paint as well as blow dust from the surface during cleaning. Clean air is critical. Worn or improperly maintained compressors and air systems are responsible for most paint failures. Compressors use oil for lubrication. Some oil passes into the air lines and eventually ends up in or on the painted surface. Paint and oil don't mix. Pin holes, fish eyes, and a myriad of other adhesion problems can be caused by minute oil particles passing through the compressor to the air lines and into the sprayed paint.
Moisture condenses in compressor tanks and air lines, so it must be drained regularly at the compressor drain valve and at a moisture trap in the air line system, either at or before the air regulator valve. These valves should be opened and drained regularly to remove as much oil and moisture as possible. A compressor of at least five hp is generally necessary to supply adequate air volume (measured in cubic feet per minute) for a spray gun. A smaller compressor may force you to stop periodically during painting to wait for it to build pressure. This can not only be irritating, but it also affects the quality of the job.
A relatively new paint spraying system is called HVLP (High Volume, Low Pressure). Here, the spray gun operates on a somewhat different principle than the traditional siphon spray gun. Paint is applied in higher volume at low pressure (under 10 psi, as opposed to 45-70 psi for siphon equipment). Manufacturers recommend a minimum compressor of five hp. virtually all HVLP guns today require 10-11 cfm at 80-100 psi going into the gun to have 8-10 psi at the air cap, where the paint is atomized.
Paint transfer efficiency is greatly increased with HVLP gear; up to 80 percent of the paint ends up on the car, compared to 40 percent from a high-pressure siphon gun. This reduces pollution and paint costs. One trade-off is price; HVLP paint guns are considerably more expensive to buy, hardly worthwhile for one-time use.
If you are in a confined space and do not have proper extraction facilities use an HVLP gun.
There are many standard paint guns to choose from, made by Binks, Sharpe, Matson, DeVilbiss, Sata, and Optima. They are suction, gravity flow, or pressure-pot oriented. Standard guns are much less expensive than HVLP equipment and are readily available used. For the price of a rebuild kit and a little time, they can spray like new.
The higher the air pressure at the air cap of the spray gun, the flatter (more evenly) the paint will lay on the panel. However, more paint is atomised and will just blow away and miss the car. Practice and experience will help you to find an adequate compromise.
Paint Safely
When working with any paint or primer, always wear protective breathing masks with filters (charcoal) that remove chemical fumes as well as solid and dust overspray.
Use a respirator when spraying isocyanide-cured urethanes (2 pack).
Since isocyanide is a cyanide, the paint industry has found it prudent to go much further with protection from emitted vapours. Full body suits, boots, rubber gloves, and air masks with a constant supply of fresh air from the compressor are essential.
Don't paint isocyanide products with anything but full protection. Isocyanide attacks the body's involuntary systems, chiefly the central nervous system. Entry is not just through the respiratory system but also through the tear ducts of the eyes and any exposed skin. Initial out-gassing or drying of urethanes is equally hazardous. Failure to use respiratory protection is akin to driving without brakes.
Choosing Your Paint
The first step in the actual painting (after priming) is to apply a coat of sealer, which provides a uniform background for the succeeding colour coats. It also seals and minimises penetration of paint solvents into the undercoating and promotes adhesion between paint and primer. Choose a light or dark sealer, depending on your paint colour. Select a sealer recommended by the manufacturer to match the type of paint you are using.
Many paint types are suitable for automotive refinishing. Todays most common are acrylic enamel, urethane, and (decreasingly) acrylic lacquer. To make the paint thin enough to pass through the spray gun and be properly atomised by the compressed air, a reducer or thinner must be added.
Acrylic enamel paints, especially urethanes, require addition of a catalyst, which chemically hardens the paint in much the same way that adding catalyst to fiberglass resin causes the resin to harden. Acrylic lacquer needs only a thinner to reduce its viscosity before being sprayed and requires only air drying.
Paint type is a matter of personal choice. For home use I would say cellulose is you paint.
For show quality paint work
I prefer acrylic lacquer. A typical lacquer job requires 12 to 24 coats. Drying time between coats is minimal, usually only a few minutes for the solvents to "flash off" (evaporate). Six to eight coats are applied, then the paint is allowed to dry overnight. Within the next few days, depending upon the weather, the surface is water sanded with 500-grit wet sandpaper to remove surface unevenness (orange peel) and dust particles. After being thoroughly cleaned of the wet-sanding residue, the dried surface is wiped with the tack rag, and another six coats are applied, each succeeding coat being reduced slightly more. Initial coats should be thinned 1-1/2 part thinner to 1 part paint. The last two coats are at a consistency of 3 parts thinner to 1 part colour. For the last several coats, I use a slower-drying thinner to increase the flowing out characteristics and gloss of the lacquer.
Acrylic enamels and urethanes are applied similarly to lacquer. Fewer coats are needed, though, because more paint is applied with each coat with heavier viscosity (usually 1/2 to 1 part thinner to 1 part paint).
For metallic colours, application of a clear coat over the colour is essential to protect it. With acrylic enamel and urethane, generally three coats colour and three coats of clear are appropriate; with lacquer, usually six to eight coats of colour, followed by six to eight coats of clear.
Putting the paint on
Painting requires a thorough reading and full understanding of the paint manufacturer's directions. If mixed exactly according to directions, an acceptable finish can be expected once you understand the spray gun to be used.
For best results, a properly filtered and ventilated professional paint booth is a must. You may be able to rent one by the hour in some places. Dispose of excess paint, thinner, and clean-up materials properly. Environmental concerns mean that fewer and fewer amateurs paint cars.
Spraying Techniques
Spray Gun Patterns:
A. Guns can be adjusted to round or oval patterns.
B. Top-heavy pattern caused by partly clogged horn holes, obstruction on top of fluid tip, dirt on air cap seat or fluid tip seat.
C. Heavy bottom pattern caused by partly clogged horn holes, obstruction on bottom side of fluid tip, dirt on air cap or fluid tip seat
D. Heavy right side pattern caused by partly clogged right side horn holes, dirt on right side of fluid tip, or clogged air cap right jet.
E. Heavy left side pattern caused by partly clogged left side horn holes, dirt on left side of fluid tip, or clogged twin cap left jet.
F. Heavy centre pattern due to low setting of spreader adjustment valve, low atomising pressure, or paint too thick; with pressure feed, paint pressure too high for atomization air, or paint flow in excess capacity of cap, too large a nozzle for paint used, or too small a nozzle
G. Split pattern due to improperly balanced air and paint; reduce width using spreader adjustment valve or increase fluid pressure.
Spray gun, clean and in good condition, properly atomizes and applies the paint in a minimum of time. Spray guns generally have two adjustments. The spreader valve, usually near the head of the gun, regulates air flow that controls the spray pattern, from round to oblong. Turning down the air spreader valve reduces air to the two horns in the spray gun head and produces a round pattern. Opening the valve flattens the pattern, producing a more oval shape. Not only can the shape of the pattern be varied, but also its size. The spreader adjustment is the key to economical painting. Never use a pattern wider than the surface being painted.
The fluid adjustment controls the amount of paint flowing from the gun. Spot jobs, for instance, require low paint flow; overall panel painting requires maximum flow.
Depending upon the type of paint and its viscosity, air pressure is adjusted to atomize the material. An air regulator, at the gun or at the air filter/transformer, controls the atomizing air pressure. Correct pressure, a matter of experience, is arrived at by spraying a series of test patterns (see diagram) Pressure at the siphon-type gun is normally 40-60 psi.
Too low a pressure results in an under-atomised, or orange peel, surface. Too high a pressure wastes paint, leaves a rough, dry finish, and may also create orange peel.
It is important to spray at the correct distance from the panel. Enamels and urethanes are usually shot from 8-10 inches away, about a normal hand span. Lacquers are sprayed from 6-8 inches away. Get too close, and the paint will go on too heavily and run. Too far away, and the paint can be dry and sandy.
Hold the gun at the correct distance throughout each stroke. It should also be perpendicular to the surface. If the surface is angled more paint is applied at one end of the spray pattern, less at the other. Work for a wet coat. Use slow, steady strokes. Never fan the gun from side to side; keep your hand and the gun square to the surface. To ensure proper coverage, overlap each stroke by 50 percent, i.e., aim the centre of each stroke at the edge of the previous one.
Pull the trigger at the beginning of each stroke at the edge of the panel you're painting. Continue the stroke to the other edge of the panel, and release the trigger there. Your stroke should be smooth and easy, slow enough for sufficient material to be applied yet fast enough so that not too much goes on, which causes sags.
To minimize the amount of dry spray falling onto freshly painted parts—work away from the previously sprayed panel.
When spraying an entire car, plan your sequence of spraying to minimize overspray on drying adjacent panels. For example, start at the back of the right front bumper, work your way around the bonnet to the left front bumper then to the left door. Shoot the left side of the top, then the boot, the right side of the top, the right rear bumper, and finally the right door.
Painters have different methods, but the aim is to minimise overspray on drying panels. Spraying into semi-dry areas will cause heavy orange peel or rough, sandy texture.
The ideal temperature for spraying is about 70°F. Special thinners and reducers can speed up or retard drying time; use slower thinners in hotter temperatures, faster thinners in colder temperatures. Humidity is also a factor, especially with lacquer. High humidity (moisture) in the air supply can be trapped in rapidly drying paint, causing a "blushing" surface that appears chalky or dull. Spray in the lowest possible humidity.
Judging how much paint is being applied is a matter of experience. The object is to apply enough paint with each succeeding pass of the gun so that it flows out smoothly without running or sagging. Ideally, you apply just the right amount so that the paint flows out to form a surface as smooth as glass. If you pass this point, the paint begins to run.
Fixing Problems
Paint problems such as runs, sags, and dirt particles can be remedied after the paint dries.
Depending on the type of paint and temperature, this can take several hours or several days. A rubber sanding block with 500 or 600-grit wet-or-dry sandpaper is used to gradually wear down the high areas of the run or sag. (One trick is to mark the paint next to run with a broad felt-tip marker, then sand only until you see the mark begin to disappear). With non-metallic paint, you can either finish polishing or apply more coats, depending upon when in the spraying process the run occurred. With metallic paint, the area of the run must be blended, with more paint applied to even out the metallic at the problem area. Clear coats can then go on, followed by final finishing.
Dry, sandy-appearing paint is at the other end of the spraying spectrum. In this case, the paint will have a dry, rough, or dusty surface appearance. This problem can be caused in various ways. First, excessive air pressure relative to the paint flow may cause the paint to break up into small, dry particles. Second, paint that is too thick to pass smoothly through the gun onto the surface can cause a rough, dry appearance; add more reducer. (This can also be caused by using a reducer or thinner that dries too fast, not allowing the paint to flow out.) Finally, holding the spray gun too far from the surface causes paint to "dry out" en route, yielding a dry, uneven surface.
What the heck is that ?
Filler A paste that is mixed with a hardener and used to fill dents and dings.
Stopper A thin filler used to fill pin holes and very minor chips
Top stop A brand of Stopper
Celly putty Cellulose putty, a thick paste used to fill thin scratches and minor chips
Panel Wipe A chemical solution used to de-grease panels prior to painting
Fibreglass A glass strand paste used to bridge holes and for filling large deep areas
2k / 2 pack isocyanides based paint you mix with a hardener prior to applying
Base coat A coat of paint (usually metallic) that requires a top coat (lacquer)
Metallic A base coat paint which has metallic particles in it for shine
Pearl Similar to above but changes through colour spectrums with varying light
Enamel Paint used for painting engine blocks and brake drums etc
Vht paint Very High temperature paint, used for painting exhausts & manifolds
Underseal A thick tar like paint used to cover the underside of the car and protect it from the elements. (Can also be purchased in clear)
Lacquer A clear top sprayed over basecoat to give the shine
Wet and dry Sandpaper in varying grades the higher the number p2000 the finer it is, use with soapy water to smooth paint (soap prevents the paper clogging)
Rubbing compound A gritty polish that smoothes the paint surface and brings the shine up.
An excellent piece of information..... would have been haven if some pictures were also available.e.g different stages of preparation, types of tools used. etc.
