Water Oak end grain spar urethane finish bubbling up
Three months ago I salvaged a stump from a large water oak tree in our yard in Dallas Tx. The tree wasn’t dead but was dying so the wood was green. I treated the stump like I do logs I am going to turn with Anchorseal2. A month ago I planed and sanded the top surface and applied many coats of Minwax indoor/outdoor Spar Urethane sanding between coats. The stump sits on our porch. Over the past two weeks the surface has begun bubbling up only in the outer 6 inches of the stump which I suspect is moisture. I did not expect this to happen to spar urethane. Is there anything I can do to eliminate this issue?
Replies
I could be wrong, but I think the "cookie" is not yet dry and you are getting some mold/mildew under the urethane you have applied.
Anchor seal is not a treatment, it’s a coating that prevents drying. Spar varnish will protect dry wood from the environment but a wet log will still attempt to dry having moisture push through the finish.
If you are able to sand the urethane off to bare wood and soak the cookie with Pentacryl. That will drive the moisture out more quickly and once it gets to the proper moisture content recoat with Total Boat.
Thanks for your response. Are you suggesting Total Boat because it is your preferred outdoor finish or will it actually prevent any remaining moisture from bubbling up?
You would use Total boat after you have gotten the moisture content down, not that it will prevent the moisture from coming out of the cookie. Once you are sure that the cookie is dry, Total boat is a really good durable outdoor finish. Give the folks at Pentacryl a call, they are very helpful and you can describe to them how much moisture you think still remains in the cookie, the dimensions of the cookie, and they can give you an idea for how long it will take to get the cookie dried.
Thank you!
Your cookie is a long, long way from being dry. It needs to be dry before finishing.
The heartwood of all trees is dead. Only the sapwood is alive. That's why the heartwood isn't bubbling, but the sapwood is. Clearly, what you have there is zombie sapwood.
Second that, about being a long way from dry. You say it was dying and there is no centre rot, so it is decaying in the sapwood and it will be somewhat punky, and may never look good even if it does dry eventually. The centre looks like a natural clock face, though. Looks like it may be tall enough to sit on, so you have a lot of wood there.
Yes. Quite the learning experience. Should have asked my tree people with big chainsaws to create a cookie rather than a stump. Was worried about the thickness being too uneven. At least I know more now about wood than I did 2 months ago.