BMW April 2022

As a magazine, over the years Automotive Refinisher has always tried to show the latest spray painting and preparation techniques. A recent request from some of our entry level spray painters who dominate the small repair market right now, needed some tips and answers about spray painting techniques.
One of the most significant failures of these operations comes from a basic lack of understanding atomisation as they operate the controlled explosion of solid colours and transport them onto the substrate being sprayed out. Automotive Refinisher feels that in a way we can help out a bit here with some of the basic principles of success in attempting to overcome and evaluate problems.
It is best to remember a few things when you are spraying. It’s a toxic fluid like all paint which contains poison and that it creates breathing irritations because of the isocyanate in it. Hardeners can’t make a painter become desensitised with constant bouts of asthma. If this happens the only option left for a spray painter is to find another job away from 2K materials. These substances also cause problems with spray painters’ eyes and can enter the skin through overspray landing on the spray painters arms, hands, etc, so always treat these products with respect and always use the best safety equipment.
Reading the labels and following recommendations from the paint suppliers of choice, together with the combination characteristics for fire and explosion are all explained in general terms on COSHH product handling sheets.
One thing a DIY specialist spray painter has to get in his head straight away is to have a no reject philosophy. In short you only get to paint something once to get the repair right.
You are paying top dollar for the quality product you are using, so it’s going to take every bit of effort to do a perfect repair.
I would like to talk a bit about compressed air, for more often than not, spray painters don’t have enough air capacity and in general terms this will limit the use of an air fed respirator system. Buy the very best twin cartridge protective spray mask as you are going to need it to survive in this business.
Lastly, on the TDI Health headgear front, If you ingest the overspray, it forms sticky carcinogenic particles in your lungs that ultimately end up being lung cancer. And the question you probably are asking right now is: why are we using such a total health hazard every day in the paint shop? Well the answer is simple. 2K paints give the 8-10-year external durability and it holds up better on vehicles than other product formulations that are currently available.
Here are some of the top tips to help you get the best DIY spray paint done.
Start smooth, finish smooth
Spray paint typically has a sheen that, when dry, reflects light and emphasises any surface imperfections, including scratches, dents and nicks. Before spraying on the final coat of paint, you must sand the surface smooth and then apply at least two primer coats. Be sure to sand between each coat. You can brush on the primer, but spray primer is much quicker.
Applying a primer and then sanding is especially important when spray-painting wood because the first coat of primer will raise the wood’s grain, creating a fuzzy, rough-textured surface. Sanding the primer with very fine sandpaper – 180-or 220-grit – will knock down the raised grain and leave behind a smooth surface for the next primer coat. Finally paint the topcoat.
You can use an orbital finishing sander, but hand sanding with a sanding block wrapped in sandpaper is just as effective. If you don’t want to buy a sanding block, make one from a short length of 1×3 or 1×4. After sanding, be sure to use a tack cloth to remove any sanding dust before applying the next coat of primer or paint. Remember, the key to a smooth finished coat of spray paint is starting with a sanded-smooth, primed surface.
Fast finishing of small parts
To spray paint small fasteners, such as screws, nails, bolts, cup hooks and screw eyes, try this trick: Stick them into a sheet of cardboard. Stand the cardboard up—preferably outside—and then spray on the paint.
For bigger projects, use a big dropcloth
To capture overspray when spray painting larger projects, don’t waste time taping together sheets of newspaper; they’ll only rip and fall apart as you paint. Instead, spread out a large plastic or, better yet, canvas drop cloth. That’ll provide plenty of protection from overspray as you apply the paint.
Do a spray-pattern test
Before spray-painting the work piece, shake the can until you hear the mixing ball inside bouncing around. Then shake well for at least another 90 seconds. Now, and this is important, test the can’s spray pattern by spraying some paint onto a large piece of cardboard or scrap plywood. Once you see the spray pattern, you can adjust your technique and determine how far away from the work piece you must hold the can.
Also, when spray-painting large or long items, start spraying an inch or so off the near edge of the piece, and continue spraying all the way across and off the far edge. Stay a consistent distance from the piece and hold the can parallel to the surface. Don’t sweep your arm back and forth in an arc.
Use tough paint for demanding jobs
When you need a high-gloss coating that resists rust and chemicals, take a tip from the auto body industry and step up to a 2K (two-component) spray paint. Like epoxy, the resin and solvents stay separate until you’re ready to paint.
Clean and prep
Another great crossover from the auto body industry is rubbing compound that cleans and abrades the surface at the same time. It’s great for buffing out scratches – but can also be used to prep the surface prior to spray painting. Just be sure to clean off any compound residue before painting.
Handy tips
The 2K Solid Colours Guide will help you to find a closer colour formula in quick time.
Prepare surfaces or primed surface areas to P800-1200 Wet finish.
Areas required to have colour blended should be finished with a grey scourer pad or P1200-1500 Wet.
Use wax and grease remover to thoroughly clean surfaces using a wipe on-wipe off method.
Use a tack rag to wipe surfaces gently prior to spraying.
Recommended spray gun is 1.3 – 1.4mm fluid tip, 25-30 pi spray pressure.
Mix 2K solid colour with 2K hardener and 2K reducer to the recommended rate.
Strain thinned paint using a proper paint strainer before use.
Apply one single medium wet coat.
Allow 10 minutes to flash off.
Apply a second full wet coat.
If recommended on technical data sheet apply a third coat after 10 minutes of flash off.
Check job for adequate coverage and gloss.
Always have a tin of silicone remocer in stock to avoid surface contamination.
Allow to dry to recommended times.