Oil paint dries extremely slowly, and even if the surface feels dry, the paint underneath might still be wet. When using oil-based paint, you should always keep these two rules in mind: 1) paint lean to thick (or “fat over lean”), and 2) never layer acrylics over oil.
Make sure any loose paint is removed and you've sanded the surface smooth. Apply a good oil-based primer and once that has dried, sand it with 120 or 150-grit paper until you feel a completely smooth surface. If you start with brush marks in the primer, then there is no way you'll get a smooth surface for the paint.
Oil paint dries slowly, so if you use a high-quality bristle paintbrush, you can expect to see very few brush marks. If you want a slightly textured surface, you can use a roller; a roller with a nap of 1/4-inch or less is ideal.
How To Paint Over Oil-Based Paint. Dip a cotton ball into a small amount of denatured alcohol. Rub it over a small area on the surface. If the paint does NOT come off, it is oil-based paint and you will need to prime the surface with a bonding primer before applying latex paint.
Yes, just as you would with a paint brush. Natural fiber roller covers made with mohair or a blend of polyester and lamb's wool are usually recommended for oil-based paints, varnishes and stains.
Whether you're new to paint, or an artist who typically works in another medium, like acrylics or watercolors, it will take some time to learn oil paint's specific qualities––most notably its slow drying time and strict rules for layering.
Wool or mohair roller covers, with natural fibers, are the best choices for applying oil-based paint, but they work well with any finish and cover a variety of surfaces smoothly.
When you drag your brush across oil-based primer that is drying, the brush will leave marks and rough up your smooth surface. The only fix will be to wait until it is completely dry and then use a sanding sponge aggressively to make the surface smooth again.
If you use oil-based paints, avoid using foam rollers since they will likely absorb less or no more, thus negatively impacting the final paint job.
Proper Brushing Technique
The brushing technique used to apply oil-based paint will help to eliminate brush marks. Dip your brush into the paint and tap off the excess. Using a separate paint container is recommended over drawing paint straight from the can. Quickly coat the surface with a loaded paint brush.
It happens when the substrate underneath is porous enough to draw out the oil in the paint, which leaves behind a layer of pigment, essentially pastel. That layer is not (well) bonded in a paint film. It also happens when adding a layer of paint over drier paint, and it tends to happen to earth colors.
Adding a Second Coat
After your first coat of paint is dry, it's safe to recoat typically after four to six hours. A good rule of thumb is to wait at least three hours to recoat your paint or primer if it's water-based. Waiting 24 hours is best for oil-based paint and primer.
What Can I Use To Thin Oil-Based Paint? A solvent like mineral spirits or turpentine is usually the simplest way to thin oil paint because they are low viscosity and thin the paint very quickly. Solvents can also make the paint more watery because of their low viscosity.
Oil-based primers take at least eight hours to dry. You may have to lightly sand the primer over smooth wood surfaces with 180-grit sandpaper to provide an easier bonding surface. Be sure to wash away any dust caused by the sanding and allow the area to dry before adding your paint.
Actually when you apply oil-based compound over a just dried-up surface of the very same compound it binds perfectly without any sanding. Adhesion is so perfect layers never come apart - rather they come off the covered material.
Foam brushes can be used with water- or oil-based (solvent) finishes. If you clean them immediately after use -- the real key to effective cleaning of any painting tool -- foam brushes can be used again with water-based finishes.
Start at one end, running the roller up and down the full height of the wall, moving over slightly with each stroke. Move backward where necessary to even out thick spots or runs. Don't let the roller become nearly dry; reload it often so that it's always at least half loaded.
To apply flat, eggshell, or satin paints and stains, a knit roller cover is recommended. Knit roller covers can pick up and release higher amounts of paint than woven fabrics because the fibers have a looped backing with a single pass-through process resulting in a more “open” fabric.
Each roller has a different thickness of fabric or “nap”, specifically designed for different surfaces around the home. The thicker the nap or length of fabric, the more paint a roller will hold. The thicker the nap, the rougher the surface the roller is designed for.
Try wet-on-wet versus dry brush
Paints will blend on the canvas when working wet-in-wet, which is great for creating transitions or gradients. Painting with a dry brush will give you a more textural effect, which is perfect for painting brick or dirt.
Unlike watercolors, acrylics and other water-based paints, which can be thinned with water, traditional oil paint must be thinned with solvents. The oil molecules in the paint can only be broken down by solvent chemicals; mixing traditional oils with water does not work because water and oil do not mix.
And newer houses might have some areas of oil-based paint since it is not entirely banned: Oil-based paint is still available in quart sizes or smaller. Many professional painters even favor oil over latex for a smoother, rock-hard finish that leaves no brush marks, gaps, or bubbles.