Training - Spray Painting

I was invited by Phil Bradshaw to attend a spray painting course run by the Bodyshop in Wellington. His club (Constructors Car Club) made the approach to The Body Shop to put this on for their club members. I hadn't seen a course like this run in Auckland so leapt at the chance to attend this one in Wellington when Phil invited me. The timing couldn't have been better as I have been thinking about throwing some paint at the Ford Pop not to mention being able to paint the Coupe Chassis and many other parts like the driveshaft and other under body parts that will be mounted.

This first course was about removing the old paint, attending to the bare steel to kill any rust and then onto laying down etch primer, filler primer and surface primer. It also covered the application of body filler for small dents and imperfections. 

We turned up on Saturday morning for the course which would be run in Bodyshop's warehouse. They are a panel and paint supplies outlet, supplying the public and the trade. Its a pretty well set up affair with plenty of stock and they even have a spray booth on site.

When we arrived we were greeted with the panels that we would be working on during this first course (one of three) that would cover paint removal, panel prep, priming, primer filling, sanding, and repairing dents.

We were supplied with a safety mask and overalls to wear and there was a good supply of solvent resistant latex gloves on hand. Kevin who ran the course, firstly went over a few tips about the gear and the materials we would be using. The safety mask we were given uses filters and pre filters to screen out the toxic fumes that come off the paints and thinners. He suggested when these masks weren't in use that they should be stored in a plastic bag and preferably away from solvents and paints. If you don't do that the filters will continue to absorb those vapours and be less effective in a shorter time, than if they had been stored correctly. Good advice.

With the paints there are 4 types predominantly used. Acrylic (or water borne) 2 Pack (uses a paint and a hardener) Lacquer (base coat and clear coat system) and Enamel.

Acrylic is being used more and more as it is eco friendly and washes up in water. It requires some fairly good conditions to use it in (ideally a spray booth where the paint can be baked) as it relies on the water in the paint evaporating in order for the paint to dry/harden. For home use this is not impossible but it does make it a little less attractive as an option. It is also more expensive. While this is the safest paint to use it is interesting to note that there is no water based clear coat yet so you still have to use the lacquer based clears.

2 Pack is very quick as it creates a nice shiny finish straight off the gun. It is a really hard finish and doesn't require clear coats over the top, so its quick. Its probably the most common paint these days because it is fast and gives the hardest wearing finish. The issue though is that it is incredibly toxic being full of isocyanites. To be honest I am scared of the stuff so won't use it at home. The consensus is that it is ok if you are spraying outside and not in a confined space, but why would you even risk it.

Lacquer or base coat/clear is just that, a solvent based paint where you first spray the colour on and then spray coats of clear over the top to give a shiny finish. This takes longer and is still toxic so you need a mask, gloves and overalls, but its not carcinogenic like 2 Pack. Given I don't have a spray booth with expensive extraction and filtration equipment and don't have a suit/mask with positive air supply....but I do have time and in fact will probably find it easier to paint the things I am doing in stages, I am more than happy to stick with Lacquer. Lacquer is the next hardest finish after 2 pack.

Enamel is an older style paint and is quite hard wearing when it dries but it is very slow drying and while it is drying remains very soft. It can take weeks for the paint to harden off and when it does it is quite brittle and much less durable that 2 pack or lacquer. Lets just say its old technology and there is no point using enamel when there are much better options available.

A good tip from Kevin was to ask for the full data sheet for any paints that you buy. It will give you a lot more info than you get on the tin. All of which can be useful as you go about prepping for and using the paint. These sheets tell you things like....

• its properties
• suitable applications
• features and benefits
• ideal viscosity for applying (how thin the paint should be)
• drying time
• temp range to use the paint in
• colours available
• ratio to mix with thinners and the type of thinners to use
• how many coats to apply and how long between coats
• how long it takes to fully harden
• how to prep the surface including the grit of sandpaper that should have been used
• materials it can be used on
• recommended gun type including spray nozzle size and the air pressure to use.
• Health and Safety responsibilities

For this course we used only Lacquers as that is what the participants thought they'd be using at home most often if not exclusively.

Its useful when painting a project to know what paint is already there that you are going to remove/paint over. It is especially important if you are going to paint over, as some paints can cover the old paint and others cannot. For example you can put enamel over the top of a lacquer finish but you cannot put lacquer over enamel. It just "fries up" like you have painted it with paint stripper. So if you are painting an old car that might have enamel paint on it you need to know first what you are dealing with.

If it's Lacquer and you rub the painted surface with a rag that has thinners on it.....it will come off and you will see colour on your rag. The surface will be tacky.

If its 2 pack, the thinners won't affect the paint.

If it's enamel it will also come off onto the rag but the paint on the panel will be more adversely affected i.e. it will begin to lift.

PREPARATION

The course would follow a back to bare steel process so we could see what was involved in that. It is a good way of treating any project, but means a lot of work. It's always better to paint over an already painted surface if it is sound as this saves time, but if there are issues like rust, flaking bog, lifting paint, dents etc it's probably just as easy to go back to bare and know what you are dealing with. Be prepared to have to do a lot of work though if you find a heap of nasties under that old paint.

On the course, Kevin took us through the paint stripping process using a chemical stripper rather than mechanical. He likes to have the product do all the work for you rather than spend lots of time and effort with wire wheels, sanding discs etc as it's hard work, makes a mess and uses a lot of consumables. Also these mechanical processes can heat up and distort a panel. Stripper on the other hand is relatively easy, and if handled carefully is safe and makes very little mess.

On the course we used Tergostrip.

This is simply brushed on after roughing up the surface with 40 grit sandpaper and using compressed air to blow the dust off. You need to be very liberal with the product. On a car you need to mask off any joins as you don't want the stripper getting in between panels. You need to be able to remove the stripper and wash any part where the stripper makes contact. You should do just 1 panel at a time right up to primer stage before starting another panel. After stripping and prepping a panel it needs to be primed within 2 hours or it will start to oxidise/rust again in its raw state while exposed to the air.

When using stripper you need latex gloves as it burns on contact with skin. You also need glasses as you wouldn't want any to flick into your eye. Wear your mask too as it is a bit fumey. A hot tip here is to be careful when you finish applying the stripper.  Don't remove your glasses or mask if you still have your gloves on and they have stripper on them. You will transfer that to your scalp or face and it burns like a bastard.

After the stripper is applied you cover the surface with a plastic drop sheet to lock in the chemical reaction and vapours. Leave it for 20 mins or so and peel the plastic back. You can now begin removing the blistered paint with a scraper. Let the scrapings drop into the plastic drop sheet for easy disposal.

Once done, if you have a lot of paint that is still hard to remove, just repeat the process. That next layer will be soft so the second coat of stripper will deal with that quickly. Once you have a mostly bare panel, you wash the surface with a wet watery rag which will neutralise the stripper. This should be rinsed and washed several times. 

You may still have a few remnants of paint that can be rubbed off with 2 way thinners or may need to be sanded off using an orbital sander. If there is a lot of bog left you may need to use 40 grit paper, otherwise 80 grit will suffice.

Wash the panel down using Prepsol. Prepsol is a cleaning solvent that will remove waxes, grease, finger residue and other contaminants like silicone and polish. It will not affect the surface. It's applied with a lint free cloth. Use it liberally BEFORE sanding and before undercoating. Wipe off excess with a dry cloth. Use SPARINGLY before any topcoat.

DEALING WITH RUST

We asked what we needed to do now to deal with rust particularly inside a panel e.g. an old door where you can't get to and won't be painting. There is a product called Neutra Rust 661 which is a rust converter. This can be brushed on, or for the inside of a panel it can be sprayed on using a spray bottle. In this first pic you can see the milky solution. 

In this next pic it has neutralised the rust and converted it to a black carbon like surface. This can now be covered with any commercial internal panel protectant like Tectyl, Fisholine or other wax based protectants.

For the outside of the panel you can use this product also but would probably remove the rust mechanically particularly if it was serious i.e. needed to be cut out and the panel repaired. 

For surface rust on the panel though, you can use Deoxidine. Remember to Prepsol first though! Deoxidine is a phosphoric acid metal cleaner and conditioner which removes rust, destroys rusting agents and leaves the metal surface chemically clean and ready for paint. 1 x 500ml bottle will do a whole car. You apply this (mixed 2 parts water 1 part deoxidine) with a scotchbrite pad lightly rubbing across the surface. The rust will be removed. Once done, wash the surface with water (within 3 mins) and quickly dry off with a dry rag and dry compressed air. Dry and blow out any joins. You need to apply paint within 2hrs of this process being completed.

Wipe the panel down with Prepsol. You are now ready for the etch primer. Here is the panel I prepared and treated with deoxidine before cleaning with prepsol.

Cleaner than a clean thing with clean written on it....and in the spray booth ready for etch primer.

ETCH PRIMER

iCoat Etch Primer is an anti-corrosive primer that etches and provides good metal protection. It can be sprayed straight to bare metal in 1 or 2 even wet coats. It can also be brushed in small areas. iCoat is a "Holding Primer" which means it can be left uncoated as a matt paint finish. It prohibits moisture absorption.

You can now do your spot rust repairs and the rest of the panel is protected.

If you get it all right this is the sort of finish you can get...and yes that is what I sprayed! Under close supervision of course.

And here it is once dry.

You CANNOT put lacquer base coat or clear over this. You need to spray on Autothane Primer 1k first.

PRIMER vs. PRIMER FILLER

You can use Autothane Primer 1K Filler as a surface primer (2 parts) or as a filler primer (4 parts) using two way thinners to thin it down. Primer won't fill 150 grit scratches but filler primer will. For Primer you need to sand it with 180/240 grit first.

If your first coats are filler primer you should prep the surface with 80 grit, apply the 3 or 4 coats of filler then wait 2 days before sanding with 120 grit. Then you can repeat or just use one coat of filler and sand using 240 grit and go to surface primer. Always DRY SAND!

Don't have the car in the elements in primer it is very porous and will allow water through particularly if there is no iCoat etch primer underneath it. You will then get bubbles of rust coming from underneath.  Top coat is the only truly waterproof layer. Its important to understand this and NEVER use wet and dry sanding techniques with primer. Use dry paper only.

If you have a lot of imperfections to deal with you can spray up to 4 heavy coats of filler primer (2mm or even a 3mm nozzle) at any one time. Guide coat or use guide powder and sand with 120 grit. You can then apply another 4 heavy coats of primer filler if need be. If this isn't dealing with the imperfections you may need to use body filler.

For demo purposes we masked off one side of the panel so we could see how much build up the filler primer would deliver.

Here is the panel with two good coats of filler primer applied. It was quite amazing how thick this was.

SOME EXTRA VALUABLE INFO

SPRAY GUN

You use the following nozzles for the following applications.

1.4m nozzle = Lacquer Topcoat. No good for primer

1.7m nozzle = Chassis or components where you need a good coat of paint but aren't so concerned about finish

2.0m nozzle = Surface primer and lighter filler coats

3.0m nozzle = For heavy primer filler coats

Gravity fed guns atomise better.

A 600ml cup is big enough for most uses.

The gun we were using on the course was available at a reduced price so I grabbed one, knowing that it came recommended and of course having test driven one.

GUN ADJUSTMENTS

The main adjustments on a gun are the fan control and trigger control. The fan control allows for a narrow fan or wide fan spray pattern. A narrow fan will put more paint on in a concentrated area. You need to overlap closely. A wider fan puts paint on more thinly over a wider area. You can go wider with your overlaps. Rather than adjusting fan consider painting closer to the surface or further away to get similar benefits.

The trigger control varies how much paint will feed. Don't open it right up. You'll get too much paint. As a starting point screw it right in and back off 3 turns.

If when you test spray onto one spot with a 2 second spray, and you get an even fan with surplus paint right across the fan you have the gun adjusted correctly. If however the paint is only collecting at each end of the fan and is light in the middle, your pressure is too high.

SPRAYING

When painting hold the gun about 150mm to 180mm from the surface and always with the nozzle at right angles to the surface. Do all edges first. Start by lining up the centre of the nozzle on the edge of the panel being painted to ensure good cover on the edge. For subsequent strokes you should line the nozzle up with the edge of the previous pass, i.e. 50% of the spray goes over the previous paint and 50% over the bare surface. For heavy primers or fillers this can be as little at 30% bare surface and 70% overlap.

Spray what you can reach while maintaining the same distance from the surface and always at right angles, then change position to paint further along. As long as you paint wet to wet edge it will blend ok.

When spraying get primers on wet and even noting that it's easier to sand out a run than it is to sand out "dry spray"

MIXING AND FILLING THE GUN

When mixing paints for your gun, you can use the mix ratio method for primers but for top coats you should use a viscosity cup where you time how long it takes a measured amount of the paint to run though an aperture. Too slow = too thick. Too fast = too thin.

Always stir well and filter your paint into the gun. These disposable filters like this used one sitting in the paint can, are all you need for the job.

Grab a cradle for the gun. Its much easier to fill the cup when you aren't trying to pour paint with one hand and hold the gun with the other.

Ensure the breather on the top of the cup is not blocked. This is a leading cause of spraying issues.

COMPRESSOR

The ideal compressor size is 3hp 12cfm with a 10mm inside diameter hose. Too long a hose will cause pressure drop. You should use a gun regulator so you can regulate the pressure at the gun itself. Always use a good quality moisture and oil trap. Leave the bleed valve on the trap slightly open to relieve moisture.

To clean the gun empty the paint out and add 200ml of thinners to the spray gun cup. Disconnect the gun from air and pull the trigger. Allow the thinners and paint to gravity feed through. Then add another 200ml of thinners and reconnect the gun to the air supply. Spray the 200ml of thinners. For Lacquers this is good enough for a quick clean but you will need to disassemble and clean the gun properly once you finish your project. You can though leave Lacquer primer in the gun, even overnight if need be. 2 pack time pack would harden though so you need to clean every time.

SANDING

Start with 40 grit if there is a lot of bog to remove then move to 80 grit. Can go straight to 80 if panel is in good shape. Apply filler primer and use 120 first up on a block sander as this will go through the high spots. Using a finer paper risks having the sander follow the imperfections rather than cut through. 

Move up to 180/240 grit, then you can surface prime.

Use 320/400 on surface primer then you can top coat. If you didn't need filler primer you can go straight 320/400 grit on the surface primer using an orbital sander.

If you get rub through you can touch up with a "Rub through" primer in a spray can. You can sand this and go straight to top coat.

On the course they used a Rupes sanding station. I was so impressed with this as it vacuum's away almost all the dust as you sand. Great for home use as it means all the other tools in your workshop stay clean rather than coat everything with powdered primer and filler!

I decided I'd buy one. I was impressed so much! Here's the one I bought, it came with a trolley as well.

This is the orbital sander...its a 3 which means the oscillations move in 3mm diameter circles. There is a 5 available as well for more aggressive and quicker sanding. I'll make to with the 3 as I reckon I'll get into less trouble by taking things a bit slower.

BOGGING/BODY FILLER

Prepsol before applying body filler. It must always go over primer and never onto bare steel. Use 80 grit to prep. Blow dust off and prepsol. Apply the body filler. Put guide coat or guide powder over the body filler and block sand 120/150 grit. Now filler prime and guide coat again and orbital sand. Get to 180/240 for the surface primer, then 320/400 grit and it can then be top coated. 

If the body filler has imperfections like air bubbles don't try and sand them out, use primer filler to fill them and sand again.

SUMMARY

Rough up old paint (40 grit)

Blow dust off

Brush on stripper and leave 20mins

Scrape off old paint. Repeat with more stripper if need be.

Once stripped, neutralise with water and dry the panel

Use two way thinners to remove small amounts of paint that might be left. You may also need to sand using 40 grit if there is a lot of bog. Stripper will not remove bog. If the panel is reasonably good just use 80 grit.

Prepsol the panel

Apply Deoxidine metal conditioner and scrub with scotchbrite

Wash off with water (within 3 mins) and quickly dry the panel with dry cloth and compressed air making sure you dry and blow out any joins.

Prepsol the panel

Apply etch primer to bare steel panel (within 2 hours of deoxidine) 

After 180/240 grit use surface primer but after 120/150 grit you should use primer filler.

Use guide coat or guide powder

Sand using 150/180

Blow dust off

Apply bog to any low spots

Apply guide coat or guide powder

Sand using 150/180

Reapply more bog and repeat as required

Apply guide coat or guide powder

Sand using 180/240

Prepsol panel

Apply surface primer

Apply guide coat or guide powder

Sand using 320/400 grit

Prepsol panel

You are now ready for top coat

And that is the next course.......I'll be doing that mid June so watch this space.

In the meantime I have stocked up on supplies of strippers, rust treatments, primers, sand paper, guide coat and the hardware above of course. So I am ready to go with starting on the Pop.