How to Predict that a Wood will Blotch - Popular Woodworking Magazine

How to Predict that a Wood will Blotch

 In Flexner on Finishing Blog, Woodworking Blogs

Wetting wood with any liquid will tell you if the wood is likely to blotch with a stain or finish.

A common question is: “How can I know if the wood I’m using is going to blotch when I apply a stain or finish?” This question comes up most often when finishing cherry, which has become a very popular wood.

The solution is actually rather simple. Anytime you wet wood, you create the same look you get with a finish – that is, something that changes from a liquid to a solid. So you can usually get a pretty good idea if the wood will blotch or not by wetting it.

You can use any liquid, but water will raise the grain causing you to have to sand more. Mineral spirits (paint thinner) works well as long as you’re not going to apply a water-based finish. Some residue oiliness may remain from the paint thinner and cause water-based finishes to fish eye – that is, bunch up into ridges rather than level out.

Denatured alcohol would be better for this situation because it will totally evaporate. But it evaporates quickly, so you don’t have much time to judge the potential for blotching.

One possible alternative if time is a consideration is to apply mineral spirits, then remove the oily residue by wiping with denatured alcohol.

— Bob Flexner


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