How to Apply Two-Part Linear Polyurethane
Painting with any two-part epoxy or aliphatic polyurethane paint is like taking a painter's final examination. The product creates incredibly hard, glossy and durable finish. However, because the coating cures chemically rather than drying slowly, it offers the painter a limited time frame for workability. These coatings must be applied correctly the first time, because before a painter can return to brush out an error, the coating already begins curing.
Brush Application for Horizontal Surfaces
Apply the linear polyurethane to horizontal surfaces using a roller and brush.
Prepare the surface by lightly sanding it with 180-grit sandpaper. Remove any dust from the surface before applying paint, using clean rags dampened with epoxy thinner.
Plan how you will apply the coating, including where you will start, and how you will move as you complete the project. You must always work with a “wet edge” in order for the paint to flow out and create a smooth glossy surface. This means that you should make sure that you are brushing fresh polyurethane into an edge that is still wet, rather than one that has already dried. Planing the painting path helps you to avoid problems, or in complicated surfaces such as a boat deck, prevents you from working yourself into a corner.
Mix the paint by pouring a small amount of the hardener, or catalyst into the polyurethane. Apply the paint to the surface by pouring a small amount of catalyzed paint onto the surface. Immediately roll the paint out with the paint roller. The goal is to spread the paint to a consistent mill thickness across the surface.
Quickly brush the surface of the paint lightly with a paint brush to remove the roller marks. You cannot move the paint around with the paint brush like you can with traditional latex and oil paints. After just a few minutes, the coating begins to tack up. The coating must be smoothed out as quickly as possible, and with as little rolling or brushing as possible.
Spray Application for Vertical Surfaces
Prepare the surface as described above. Additionally, tape off any adjacent surfaces that will not receive paint. The overspray from a paint sprayer will cover everything with a fine dust of polyurethane paint.
Put on coveralls, respirator, goggles and gloves. The solvents in linear polyurethane coatings are toxic, and you should not breath them in during the spraying process.
Mix the two-part coating in the HVLP sprayer bottle. Attach to the spray rig, and immediately begin spraying the coating.
Apply a small amount of the coating to a piece of scrap plywood or wall board before painting your vehicle. Test the sprayer, and see how heavy you should apply the coating. If you apply it too heavily, it will run and sag. If you apply the coating too lightly, it will look like plastic dust, and not flow out into a smooth glossy coating.
When the spray jar is empty, clean out of the spray rig before mixing the next amount of coating. Because linear polyurethane cures chemically, it gives the painter a limited working time before hardening. Cleaning each batch prevents the coating from turning hard in the sprayer
Things You Will Need
- Two-part linear polyurethane paint
- 180-grit sandpaper
- Thin nap roller, and roller frame
- Paint roller pan
- Natural bristle paint brush
- Epoxy thinner
- Clean rags
- HVLP (high volume, low pressure) spray equipment
- Masking tape
- Coveralls, including gloves and respirator