How to Paint Acrylic Urethaneby Timothy Burns
Every professional painter knows that the keys to a perfect painting job are surface preparation, and using the correct tools. These two maxims also apply in order to attain that high gloss, wet look custom automotive finish when applying acrylic urethane paints. Choosing the wrong application method, or not properly preparing the surface, leads to coating failure.
Prepare the surface by gradually sanding with multiple grit sandpapers. The final sand should be completed with 400 grit sandpaper to properly prepare a smooth surface. Use a tack cloth to remove all the sanding dust from the surface before applying paints.
Apply acrylic urethane primer coat to all prepared surfaces. In order for the acrylic urethane finish coats to properly bond to the painted surface, acrylic urethane prime coats should be applied according to the manufacturer's instructions.
Apply the primer with a high volume, high pressure compressed air paint system. Paint spray equipment falls into three categories: high volume low pressure (HVLP) sprayers, high volume high pressure sprayers, and compressor driven airless sprayers. High quality acrylic urethane paints should be sprayed with high volume, high pressure compressed air driven sprayers. These sprayers should have at least a 60 gallon compressed air tank in order to maintain high velocity air at regulated pressure.
Apply all primer and finish coats in a dust free, properly ventilated paint booth. Coatings must be allowed to dry completely in a dust free environment in order to create the deep gloss, wet look finish.
Allow the primer coat to dry completely according to manufacturer's instructions.
Applying the Finish Coats
Sand the primer coats lightly with 800 grit sandpaper. Clean the entire surface with a tack cloth to remove all dust particles.
Select the style of acrylic urethane paint for the project. Two popular styles of acrylic urethane paints are common in the industry. The single stage acrylic urethane features a high gloss, high solid count product which does not require a clear finish top coat. The two-stage approach urethane features a low gloss, high solid counter product; which is a topcoat with a clear finish coat. The following steps apply to both products, however the number of coats will vary depending on the paint style selected.
Mix the acrylic urethane paint according to manufacturer's instructions with the paint activator. Acrylic urethane products are a two-part finish. The finish coat is activated by adding a catalyst. Once mixed, the finish coat will provide a limited working time.
Spray a test coat of the finish on a sample piece, or an area of the project with limited visibility. Test the spray equipment, the prepared paint, and the application conditions to familiarize yourself with the process. Poor paint performance will result from many factors, such as a finish which is too highly diluted. Poor quality finish can also result from application temperatures which are either too high or too low. Paint which is applied to heavily is likely to create an "orange peel effect."
Apply light coats of the selected finish paint with the high volume, high pressure paint spray equipment. Allow each coat to dry completely before applying the next coat. Sand each coat in between applications with 800 grit sandpaper, as recommended by the manufacturer's instructions. If using the two-stage acrylic urethane products, apply clear top coasts to pigmented base coats according to the manufacturer's instructions. Clear top coats should be applied full strength. Do not dilute top coats with any solvents before application.
- Clean paint spray equipment completely with manufacturer recommended solvents between each coat of paint. Clogged or dirty paint spray equipment is the number one cause of spray finish related imperfections that could ruin an otherwise beautiful paint job.
Items you will need
- Acrylic urethane paint
- High volume, high pressure compressed air paint system
- High quality paint spray gun
- 60 gallons compressed air tank and mounted compressor
- Acrylic urethane paint solvents
- 200, 400, and 800 grit sandpaper
- Tack cloths
- OSHA approved paint respirator mask with carbon filtration
- vintage american muscle car close-up image by Steve Mann from Fotolia.com