Thursday, September 16, 2010


The quality of the paint finish is wholly dependent on the quality of the preparation. The entire area which is to be sprayed should be flatted using increasingly fine grades of wet 'n dry, used wet (except on bodyfiller,
which would absorb the water). Begin using a coarse grade of 400 grit then progress through to 1200 grit for the final finish. The surface to be sprayed should be perfectly smooth with no ripples. Use a flexible straight edge to check for unevenness in filled areas. When the finish is acceptable, begin masking off. Masking tape and newspaper is quite acceptable. Avoid using plastic sheeting. because the paint will not adhere strongly to this and will quickly dry to a powdery dust which can be blown around the workshop and on to the painted area before it has dried. Large plastic (dustbin liner) bags are, however, ideal for quickly masking off wheels.
When the masking off is complete, damp down the floor. Clean the metal using a tack cloth, which will remove all traces of paint and filler dust, then finally use spirit wipe to remove any traces of oils or greases.
All types of paint have to be thinned before they can be sprayed. The paint manufacturers produce data sheets which will give the correct concentration for the paint being used. Stir then strain the primer before thinning it, because even 'new' paint can contain stringy Lumps which clog the paint spray gun. An old stocking can be used to strain the paint. After adding the appropriate amount of thinner, stir the mixture well before pouring it into the spray gun. You can obtain special cups which you can use to gauge the paint/thinner solution viscosity by allowing a set amount to drain from a hole in the base of the cup and timing it, and one of these could prove worthwhile for checking the paint/thinner mixture, because the viscosity of the mixture will vary according to temperature. More experienced sprayers can judge viscosity by lifting the stirrer out of the paint and gauging how excess paint runs off. In the case of cellulose, aim to get the solution just weak enough for the paint to come off in droplets, rather than in a continuous flow.
You can now set the spray gun controls. There should be one for controlling the air flow and one for the paint needle. Set the output pressure from the compressor tank firstly to 30 psi, then open the paint and air controls fully on the spray gun. Make a rapid pass with the gun over a test surface. If large spots of paint can be seen, increase the air pressure at the tank in 5 psi increments until the rapid pass produces a suitably fine and even spray. Now adjust the spray gun air and paint controls until the correct sized pattern is achieved.
When using the spray gun, the technique is to keep the gun at a constant distance from the surface. Too close and the paint will go on so thickly that runs will develop immediately, too far away, and some of the paint will be air dry before it reaches the surface. Keeping the gun at a constant distance also gives a even spray band width. The gun should have a two-stage 'trigger pull', where stage one allows air to pass through and stage two opens the paint needle and allows paint into the airflow. The two stages can usually be felt through the trigger, and at the end of the first stage of travel there will be a discernible stop. Further movement of the trigger introduces the paint.
The technique which is preferred by the author is as follows. When making a pass over a panel, begin to one side of it and start moving the gun with the trigger at stage one, then press it fully home just before the edge of the panel is reached. Move the gun over the panel in a single, clean movement, and release the trigger back to the first stage when the far end of the panel is reached, to clear paint from the nozzle. Then repeat the exercise until the panel is covered.
Beware the 'dry edge'. This is when a band of sprayed paint is allowed to dry before the next band is applied. It could occur if, for instance, you were to begin in the middle of the roof panel and work your way outwards. By the time you came to spray the other half, the first paint to be applied would be thoroughly dry and a visible edge would result. Always begin spraying the roof at an edge, and do not spend too much time moving around the car when you have reached the middle.
When you have sprayed your first panel, allow it to dry and inspect it. You are looking especially for signs of contamination. Small dark spots surrounded by lighter circles of up to % in, in diameter are caused by oil/water contamination from the compressor, and another oil and water filter will have to be placed in line. If the surface has paint runs then you could be moving the gun too slowly, the air pressure could be too high or the paint could be too thin. If the paint begins to wrinkle before it dries then the underlying surface is contaminated, and the primer will have to be removed completely and the surface properly cleaned.
Look closely for scratches, dents and hollows which are in the underlying surface but which the primer may highlight. The problem with matt primer paints is that they can make a rough surface look quite acceptable, even though the final gloss will make every little blemish stand out like a sore thumb. Filler-primers are high-build primers which can be used over areas with small scratches, and they place such a depth of paint on the surface that flatting off afterwards can remove many scratches.
The majority of people spray on primer, flat it off and then immediately spray on the topcoats. A friend of the author, Em Fryer, questions the wisdom of being in too much of a hurry to get the topcoats onto the primer. Like all paints, primer does not harden fully for some considerable time after it has been sprayed on and, in
the casc of cellulose, this usually takes two weeks. If you spray the topcoats onto the primer whilst it is still 'soft',
then the thinners will have a much more marked effect on the underlying primer than they do after the primer has hardened. This manifests itself as marks in the topcoat which show the outline of any bodyfiller used.

The author would recommend that primer is left to harden for two weeks before being flatted and covered by topcoats.
When it has hardened, the primer may be flatted down with very fine wet 'n dry. Small scratches in the surface which now become apparent may be filled using body stopper, which should be allowed to cure then primed. Not even the tiniest scratch should remain if the car is to be painted in cellulose, because this paint shrinks, and the final gloss will show every little flaw—however tiny — in the preparation. The author prefers to remove all masking materials and re-mask the car at this stage, because over-spray on the masking materials can enter the air as a fine dust which will contaminate the final finish. Before final masking-up, go over the primer with 1000 or 1200 grit to get the primer surface really smooth, then examine it minutely — this is the last chance you get to put any tiny defects right!
Clean the entire surface again, using a tack cloth to pick up any paint and filler dust which lies on the surface. The topcoat paint should be strained and thinned, then the surface should be given a last wipe over with spirit wipe before the first of the topcoats is applied, ensuring that there is enough thinner in the paint to allow it to flow by test spraying a piece of scrap hardboard or similar. The number of topcoats will vary according to the type of paint being used. With synthetic paint, two coats will be sufficient to give a good gloss. With cellulose, you could almost add as many coats as you wish although three coats should give sufficient depth. Each extra coat should be applied around twenty minutes after the preceding one with cellulose, to allow the thinners to evaporate. You can obtain slow or fast thinners for use in warmer or cooler conditions.
Remove the masking materials as soon as the paint has dried. If you remove them too soon then dry paint dust which is unsettled will land on the still wet surface of the paint. If you remove them too late then the paint could have cured to the point at which the paint which has settled on the masking material rips at the paint on the car.
The preferred order for spraying the car is to do the roof first, followed by the roof pillars on one side of the car, then the bonnet, followed by the other roof pillars and finally the sides, engine bay lid and valances. If the interior, engine bay and luggage compartment are also being sprayed. then it is best to complete these before starting on the outside of the car.
Car spraying is too vast a subject to be coveredcomprehensively in a book like this, and so the reader is advised to seek out further reading material such as 'How To Restore Paintwork', published by Osprey Automotive. It is also worth seeking specialised advice from your paint supplier when you buy the paint.
The best advice for the person who is restoring just the one Beetle and who does not intend to make restoration into an on-going hobby is to have at least the final stages of preparation and the application of the topcoats carried out professionally. The costs of purchasing paint and reasonably competent equipment can by a wide margin exceed, that of a reasonable quality professional respray, and the potential for things to go badly wrong for the first-time DIY car sprayer is immense. Even if you cut the overall outlay by hiring good equipment, you could still spend almost as much as a reasonable professional respray would cost, but with all the attendant risks of DIY.

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