Why you need to sand an already planed board?
This is another common question we have when we are explaining the preparation process before staining S4S planned deck boards. When wood is planed it ends up with the exterior being covered with something that is called “mill glaze”
Mill glaze is quite easy to remove. All it takes is a light sanding to open up the pores of the wood. Most stains recommend a 50-80 grit sandpaper being used. Anything higher than an 80 grit will begin to reseal the wood and the stain will not penetrate.
Mill glaze is the effect that happens when the knives of the planer get hot during the planing process. When they are hot they affect the fibers in such a way that it acts as if it is glued down. You can notice it when you pick up a planed board and see the sheen it appears to have.