Whenever water or any stain or finish that contains water comes in contact with wood, it causes the wood fibers to swell, which is called “grain raising” or “raised grain.” After the water has dried the wood feels rough to the touch, and thinly applied finishes also feel rough.
Raised grain occurs no matter how fine you sand the wood before wetting it. Because you can’t prevent raised grain if you use a water-based product, you need to deal with it so the final finish comes out smooth. There are two methods:
The first is to raise the grain and sand it smooth before applying the water-based product.
This is called raising the grain, sponging, whiskering or dewhiskering. Once sanded smooth, the grain won’t raise again nearly as much as it did with the first wetting.
After sanding the wood to about 150- or 180-grit, wet it with a sponge or cloth just short of puddling. Let the wood dry. Overnight is best, but three or four hours is usually sufficient if the air is warm and dry. Then sand the raised grain smooth with the same grit sandpaper you used last or one-numbered grit finer.
The goal is to smooth the raised grain without sanding deeper than necessary, in which case the newly exposed grain may raise again when wetted. Dull sandpaper works best because it doesn’t cut deeply so easily.
Raised grain is difficult to show in a picture, but it generally appears duller, as on the right side of the accompanying photo, which was wetted, dried overnight and not sanded smooth.
The second method is to “bury” the raised grain. If you’re applying a water-based finish, simply sand the first coat smooth after it dries, just as you would do with a solvent-based finish, except with a coarser sandpaper grit—for example, 220 grit. If you’re applying a water-based stain under a water-based finish, wait until after the first coat of finish has been applied and has dried to sand smooth. Sand lightly so you don’t sand through, which might remove some of the color.