I received a question recently
about blotchy stained maple. The writer was really disappointed in the finish,
especially because he was using a stain controller. And he wanted to know what
happened.
Well, it's not unusual to end up with a blotchy finish after staining maple --
even if you first use a stain controller. Stain controllers can only minimize
blotches, not eliminate them. If you look at a piece of maple through a
microscope, you'd see end grain where you don't normally expect it -- on the
surface of the board (the same thing is common on pine boards).
How stain works. The pigments in stain don't soak into the wood fibers, they
actually settle into the pores of the wood. When stain is applied to a board
and then wiped away, some of the pigments are trapped in the pores and left
behind. The deeper the pore, the more stain it holds. The pores in the end
grain (both on the ends of a board and on the surface) hold more pigment. This
causes the blotches.
So what can you do about it? The best way I've found to minimize blotching is
to try to avoid the problem by being more selective in what boards I use. When
selecting wood, look on the edge of the board for a tight, even grain pattern
throughout. Ideally, look for boards with straight grain -- they take the stain
better (more evenly). Avoid boards with swirling patterns or grain that seems
to take off in an odd direction -- this is where surface end grain can show up
the most. After careful selection, another important step to prevent
blotchiness is to sand the project thoroughly. Sand the entire surface with
progressively smoother grits of sandpaper until you reach 120 grit. (If you're
working with a porous wood, go up to 180 grit. The higher the grit, the more
you seal up the pores.) The final sanding (using the same grit sandpaper) must
cover the entire project. If you don't use the same grit everywhere, some areas
will take stain differently than others. Once you're through with the final
sanding, finish up with the next higher grit on any exposed end grain (areas
such as the ends of shelves and door stiles). This will decrease the amount of
stain that can penetrate into those areas. As a final step, apply a stain
controller, such as Minwax Wood Conditioner. (A stain controller is typically a
diluted clear topcoat.) These products are made to partially fill the pores of
the wood and prevent the stain from building up. And remember to apply the
stain before the stain controller dries.
Go to Tip #63 |
