Woodworking is beyond a passion for me, even at work it creeps into my mind which prompted me to write up this tip.
You’ve all faced cupping before that’s nothing new, but I bet many of you have been left scratching your heads why it occurred when you applied a finish. The answer is simple, because you applied a finish to the top and ignored the underside. So the moisture is being absorbed and expelled on the unfinished underside and the cure is, to equalise the distribution of moisture by applying finish to both sides.
So what do you to rectify this now?
I take the finish has already cured and some time has passed, you need to strip the finish and lay the cup side down outdoors in a sunny spot directly on the grass without stickers. If you remember my previous post on kiln drying vs air drying, I talked about how it’s not a good idea to air dry lumber around trees or have it stickered on dirt due to the high moisture content it will receive from its surroundings. In this case this is what you want, and the rest is just observing it throughout the day. Once the cupping is removed, bring it indoors and now place it on stickers and let nature do its course.
Once the timber is dry and reached equilibrium with its environment your board should remain flat and ready for finish again but this time apply it to both sides to equalise its distribution.
That’s it your done.