A bit of light sanding creating minute scratches that improve adhesion. You will … Before starting, you need to make sure you have decided about the type of polyurethane that you are going to use on your hardwood floor. Continue applying more varnish and sanding between coats. Always work along the grain when applying and sanding the varnish. Once primer is dry, you should sand the primer before moving on to the basecoat color. Actually, sanding between coats of primer is pointless. Sanding also removes small imperfections. You do need to sand between coats of varnish. where varnish is applied in a clean-air environment, sanding between coats is never done as far as I'm aware. To create a good resistant finish, multiple coats of the polyurethane may be required on the wood surface. One tip I'll throw in here (then I'll shut up! Use 220 grit (as a rule) for sanding between coats. Recoat within 1½ hours. When you get to the last coat, do not sand it. If you do not sand between coats of polyurethane, you risk dust particles causing minor imperfections in your finish. After final coat… The sanding between coats accomplishes two things: It removes defects from the applied urethane as well as small dust particles lodge in the dry finish. Note: where de-nibbing is not needed, e.g. If you are burning through coating when you sand, it could be that it was not thick enough to begin with. You don't need the lower coat to be super-smooth because the upper coat will cover the roughness from sanding anyway. Between each coat the polyurethane must be sanded with a light-grit sandpaper. If unable to do so, wait a minimum of 72 hours, then lightly sand and recoat. Sand Between Coats of Polyurethane – on Floor & Wood Furniture: What type of product do I need to use? Although sanding between coats is not required it is highly recommended for creating maximum smoothness. It is best to sand in the direction of the wood grain, but once you get some finish built-up on the wood, you can sand in a circular pattern. This means you may have to sand the finish down and start over. I use 220 grit. Remember to let the varnish dry between coats, and to sand and wipe the varnish clean before applying more varnish. You sand polyurethane to (a) remove any dust bumps in the lower coat, and (b) cut the surface of the lower coat so that the upper coat has more surface area to bond to. As you build up the finish with more coats, you won’t need to worry as much as you will with the first coat. ), is to remember that what you are putting down for a coat has as much to do with the finish sanding experience as the sanding itself. Apply 2 to 3 more coats of varnish. For interior surfaces, apply at least three coats on unfinished wood and two coats on surfaces already finished. No one wants that. Unlike shellac and lacquer, subsequent coats of varnish do not dissolve the previous coat and need to physically bond to the previous coat. Sanding Between Coats by Alan Noel Professional Wood Finisher When applying several coats of finish to a project it becomes necessary to sand between coats to not only remove any trash that has settled into the finish but also to promote good adhesion between the layers of finish. Apply at least three coats on exterior surfaces. Just make sure you use a tack rag after sanding. Especially, as it relates to thickness of coating. From other answers on WW I understand that applying only a few coats of poly can be sufficient but traditionally you could use as … Extra fine sandpaper is often used between coats of paint or varnish.