Blotchy, uneven stain is a common problem for some species of wood - especially softwoods, like pine. Below, finishing expert Michael Dresdner explains why this happens, and how to prevent it in his response to a Woodworker's Journal eZine reader's question.
Q. Why is pine difficult to stain?
A. Michael Dresdner: "It's really quite easy to stain. The problem is making it stain evenly.
"In pine, the earlywood and latewood are very different. The earlywood is soft and spongy, and absorbs lots of stain. The latewood is harder and absorbs less stain. This often results in a photo-negative effect when the wood is stained. To make matters worse, the wood contains random pockets of sap. If you use a stain that contains the solvent for that sap (any oil-based stain), the sappy areas will preferentially absorb extra stain, creating patches of darker, uneven color.
"If you are staining pine with oil-based stain, do yourself a favor and first treat the wood with wood conditioner. Flood it on, wipe it off, and stain immediately while the conditioner is still wet. Or, seal the wood first with a THIN coat of Zinsser SealCoat. Flood it on, wipe it off, and let it dry completely before staining. Different techniques and materials, but both will result in a more uniform, albeit lighter, stain."
Rockler offers both wood conditioner and Zinsser SealCoat (so you can take your pick of pre-stain treatments) and a full line of wood stains and dies. If you'd like a deeper look into the fine art of wood finishing, Rockler also offers a number of excellent books on finishing techniques.