I learned the hardway...you need to seal the endgrain AND install glides on the bottom of each leg. Just sealing the endgrain will not prevent damage to the leg bottoms if they are dragged across a patio surface. They will catch on the stone edges and crack, chip and worse. [sad]
This is a teak chair leg that was used on a bluestone patio for several years with nothing on the bottom. When I finally saw the cracking and chipping damage that was done I added a plastic glide several years ago which helped a lot, but it didn't prevent the wood from continuing to split more because of wicking up water.
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I've been refinishing/rebuilding all of the teak patio furniture this summer and this example may give you some ideas for your oak.
This chair leg is cracked through and will likely fail completely if left alone. After some light sanding the damage is even more obvious.
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I decided to use Smith's Clear Epoxy Penetrating Sealer to seal the endgrain and to reinforce/stabilize the chair leg, it's popular in the marine industry. The whole process goes pretty fast because as you apply the epoxy it wicks quickly into the endgrain. I'll apply the epoxy to 6-8 chairs and by the time I've done the 8th chair, the 1st chair will need another coat. Just keep applying and mixing more epoxy until there's a nice smooth continuous surface on the chair leg. This photo is after 6 coats of epoxy.
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At this point there are 20+ coats of epoxy applied and water will never be sucked up in the endgrain again.
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You can see how the epoxy wicks into whatever voids there are which also stabilizes the wood.
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After sanding and 2 coats of teak sealer along with a white plastic glide added to the leg, this chair is back in service.
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