I built a Bar out of scrap materials and used solid red oak hardwood flooring a friend of mine had as the Bar top. Pretty nice right?
Here's the stupid part….it's an outside bar.

I used liquid nails and nailed it down to 3/4 pressure treaded plywood. Then I siliconed the entire perimeter and applied 3 coats of exterior polyurethane. Guess what….it wasn't enough protection against the humidity and rain (go figure), and all the boards are now cupped at each seam.

I'm planning on belt sanding it all down, but can anyone suggest anything I can do to make it weather proof??

It turned out real nice ( I even added lines to make it a shuffle board table) so I won't stop until I find a solution.

Thanks in advance and feel free to call me every name in the book for attempting something like this in the first place.

If you can keep the water from getting underneath, you may have success!

The moisture is collecting under the wood, making the bottom of the boards wetter then the top, which is drying out. Thus the bottom of the board is swelled/expanded and the top of the board has shrank/contracted. The effect... cupping.

Clear pentetrating epoxy sealer should work well for this. It is a an excellent sealer used on wood boats but expensive.

Keith