Question about sealing my wood deck

I have a semi V 14 foot boat, with the 3 tank seats inside. I have glued 2 sheets of tounge and groove together and cut them to shape...but the wood is not marine or treated. I have read on here that people use polyurethane to seal it, but others have told me that poly is still poreous, which is why you get rings on your coffee table, etc.

I have only put one coat of this stuff on each side, and was thinking about putting a coat of fiberglass resin/bondo around it instead of doing more coats of poly....it really costs about the same...and since I dont need it for strength, I woudlnt need the fiber mesh necessarily....

I will be using carpet, putting in a livewell, etc. But really want to get this wood sealed from the water.


Any thoughts? Its 3/4" wood - actually called "sturdi-floor" used below floors as the name suggests.

Personally, I'd go ahead and give it a couple more coats. The polyurethane works, but some Marine Spar Urethane (made by MinWax) may hold up better to a wet environment, as long as it's not submerged continually. Be sure and seal all of the edges of the wood real well.

Ok - I am using a spar urethane as opposed to the regular stuff, but it did not specify it was marine....so there is an outdoor spar and a marine spar?

What about my comments about the fiberglass resin?

I used Cabots marine grade Spar Varnish. It states that it is suppose to out perform normal urathane and can be used on boats above the water line. Here's a link to the specs https://www.cabotstain.com/products/product/Spar-Varnish.html

The last time I used fiberglass resin it lasted for a little while and then ended up cracking and the flaking / peeling off. I just went with 3 good coats of Cabots and then put a couple of coats of paint on top of that for any of the wood that isn't getting carpeted.

I was afraid of the cracking with weight and any deflection in the wood from weight....

I will look into the marine varnish/urethane.

I just used 3 really good coats of thompsons water seal on mine