How to apply oil based polyurethane WITHOUT the pits and bubbles.

The reason for this thin coat is simple. The first coat of poly is only meant to fill up the woods pores, and bring the finish to the surface of the wood. Any more than this and most finishes will get rough and pitted. So if you apply a heavy coat of finish to bare wood, it will dry so rough that in most cases you will have to sand almost down to the wood surface anyway. And if there are contaminants in the wood, (waxes, silicones and oils) this heavy first coat will take a long, long time to dry. The drywall towel applies a thin measured coating of poly, just enough to top up the pores of the wood, and it most always dried overnight in a warm 70 F floor. Notice how I say a 70 F floor, because if you have a crawl space under the floor, your floor surface may be too cold for any finish to dry properly. The wood itself needs to be 70 F.

I use the same finish for all three coats. This makes touch-ups a lot easier in the future. I never use a special oil based sealer, this is just a thinned finish and as you see you can make your own. And never use a lacquer sealer. Just read about this terrible and flammable stuff in the Floored News section.

And that’s the key to a successful finish, each coat must dry thoroughly before you apply additional coats. How do you tell if a finish is dry? Well and experienced floor mechanic will smell the excess solvent in the floor, and sometimes just feel the finish; it may have just a touch of tackiness to it. But the acid test is to get the floor buffer on it with 100 -120 grit screen. Start in the far corner of the room. If the finish gums up you won’t make too much of a mess. Run the buffer on the floor for about a 1/2-minute gently moving it back and forth. Stop and check the screen. If it shows any signs of gumming up, quit and wait another 24 hours. Most instructions on finish can labels are way too optimistic, and don’t allow for the variables that will occur in floor finishing. Floors are large areas, so at the very least that can double the dry time (as say a tabletop) as there is a lot of solvent to be released. And there are always contaminants in old floor and sometimes new floors. Some tropical wood cannot be coated with poly, and even eastern white pine with its numerous pitch pockets can take days between coats, to set up. The same hold true if you are simply sanding by hand between coats, if the paper gums up, and the finish doesn’t powder, wait at least 24 hours. Too many problems in the next coats are caused by failing to let this coat dry out. Failure to head this warning will make at best a weakened finish or at worst top coats that won’t dry.

And this goes double for those you who want to stain the floor before you apply three (yes 3) coats of poly. All pigment stains contain a binder that allows the pigments particles to stick to the pores of the wood. This is a form of varnish, in the slower drying so called oil-based stains. And in all cases this stain needs 24-72 hours to dry. If you coat over a stain too early it will definitely interfere with subsequent coats, and you will have no end of problems. It’s typical that the poly won’t dry or stick to an undried wood stain. Know your stain, and it’s compatibility with the finish you are using. Do a test in the corner of the room. Let the finish cure (15-30 days) then do an adhesion test. Cross hatch the test spot to the bare wood with a razor apply duct tape and rip it off. If it peels use another stain or finish. If you are using the same brand of stain and finish, most times you will be OK. But with differing brands, you will take your chances until you do the above test.