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I watched several of your videos on finishing. I decided to try the “Seal Coat technique” you showed in the video. I had 3 basswood carvings and one aspen carving that needed finished. I brushed on the Seal Coat to all four carvings. As it was drying, within the first 5 minutes, all of the carvings started to warp (cup). They all now have a very pronounced cup.
What happened? Have you ever experienced this? Is there any way to flatten them?
This will occur when the items being sealed with a penetrating sealer are thin. It will happen even if all surfaces of the item are sealed at the same time.
The reason is a lot of moisture (sealer) is being added to the cells of the wood. As they expand on one side more than the other the wood will expand/contract causing a cup. Also, the carving on one side changes the structure of the cells on that surface making is less stable than the back side making it more prone to movement.
This is why I no longer recommend using sealer on thin carved pieces. A clear top coat finish is best like lacquer or acrylic in spray form. These dry on the surface and don’t penetrate and change the moisture in the wood.
here’s a possible fix: Apply more sealer to the cupped side to try and expand the cells and flatten the piece. When it is still wet apply weight to the other side to help it flatten as it dries. You can do this several times as needed. Eventually they will flatten out.
Thanks Marty. The pieces (3 of the 4) I had the most cupping on were thin pieces (approximately 5/16″). One of these was a piece that was highly carved (your “3 Corner Chip Trivet”). It cupped way more than the other ones. Probably the amount of carving on that piece was a factor also. I’ll try your suggested method to flatten the trivet. The 4th piece, which cupped only slightly, was a 3/8″ piece of aspen. Do you consider 3/8″ thin?
I did try to flatten the piece by applying more Seal Coat on the cupped side and putting weight on the opposite side. I left the weight on the piece for approximately 24 hours. When I removed the weight the piece was flat. However, as the day went on, the piece slowing returned to the cupped state. It was improved at all. The cup was the same as it was originally. I didn’t try to wet it again.
Oh well, I considered this all practice and experimentation. It wasn’t a piece that I was going to display or incorporate into a box or some other object.
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