Built a walnut cabinet for a client in Denver last month and the finish is already showing hairline cracks

Client wanted a custom media console for their living room. I used 4/4 black walnut with a simple shaker style door. Finished it with three coats of a water based poly, sanding between each. The house is new construction, so the air is super dry. I warned them to use a humidifier. Checked in last week and the panel on the front has these tiny cracks running with the grain. Not deep, but you can see them in the light. I think the wood moved more than the finish could handle. Should I have used an oil based finish instead for more flexibility? What's your fix for something like this?

3 comments

3 Comments

the_viola2mo ago

Three coats of water based poly is pretty rigid for a big solid wood panel in a dry house. Did you seal the back and edges of that door panel the same as the front, or just finish the show faces?

quinn_kim452mo ago

Yeah, that's a solid point from @the_viola. My buddy learned this the hard way. He built a beautiful oak door for his office and only sealed the front. He used three coats of poly on the show face, just like you said. A year later, the unsealed back sucked up all the winter air and the panel cupped like a potato chip. Had to take the whole thing apart to sand and seal the back. Now he treats every side the same, no matter what.

faithrodriguez16d ago

You said "three coats of water based poly is pretty rigid for a big solid wood panel" but honestly I think that's actually the opposite problem. The real issue isn't how rigid the poly is, it's that water based poly lets moisture pass through way easier than oil based does. So if you only seal one side with three coats of water based, that unsealed side is still breathing while the sealed side isn't letting moisture out at the same rate. That imbalance is what causes the cupping, not the poly being too rigid. You're better off either using oil based poly which blocks moisture better, or just making sure every side including the edges gets the same number of coats. Did you find that the poly itself was too stiff or was it more about the moisture getting trapped?