Sealing End Grain in Outdoor Exposures

Sealing end grain with epoxy is reported to improve outdoor durability of finishes. April 18, 2015

Question (WOODWEB Member) :
I was wondering if sealing exposed end grain on outdoor furniture, fences and gates would trap moisture behind/under the sealant (epoxy) and increase the likelihood of rot?

Forum Responses
(Finishing Forum)
From contributor R:
I think if you were to seal up the end grain right after a storm you might just seal in the moisture.

From the original questioner:
Yes, I assume if you tried to seal up after a storm then you would seal in moisture. But I am wondering if the wood was sealed when dry, somehow, moisture could migrate to the wood behind the sealer and facilitate rot.

From Paul Snyder, forum technical advisor::
Sealing the wood to prevent moisture migration is a good idea and will make the coating last longer. If moisture gets behind the film forming finish, the coating will fail and peel.

From contributor A:
I coated the end grain of a meranti picnic table (fancy) and it has been fine for 15 years sitting in the grass and dirt. I masked the leg exposing about 3/8" of the sides (West System epoxy several coats) and the ends look like plastic. There has been no change. The biscuited/epoxy miter joints have been fine as well. Those are on 3/4 x 3 1/2" wide meranti.

From the original questioner:
I understand that you epoxied the bottom end grain and up about 3/8" on the faces and sides of the legs. Were those faces and sides and other surfaces finished in any way?

From contributor A:
I initially coated it with Penofin. Itís one of those clear diluted resins with lots of UV inhibitors. Itís kind of like exterior Watco oil. Like most of us I didn't put on the yearly coat and left it for five years. After it went kind dirty I sanded it with the random orbit and then added another coat of Penofin. After another five years I sanded it and let it go grey. Now I like the no maintenance. The feet are still plastic. The moisture has plenty of surface area to dissipate through the edge and face grain. We seal the endgrain because it is a weak link (less rot resistant) and it can cause checking.

From the original questioner:
Your comments confirm my impulse to seal the end grain regardless of whether the rest is getting finished or not.

From contributor M:
The more flat/smooth you sand the end grain, the more effective your finish will be. End grain on outdoor stuff is often left sort of rough, since really most folks don't care and think it looks "rustic" or "outdoorsy" if it has some saw marks on it. Sand the end grain with an orbital sander with 150g sandpaper (give or take a grit) just like you would interior stuff, and it will last a lot longer. Itís much more likely to actually seal the wood and not have any open pores from the rough spots to allow moisture to penetrate as much.