Epoxy/Polyester conundrum

I am in the process of rebuilding a CHRYSLER Lone star 16 sail boat. The floor was rotted, and flotation foam water logged. After removing the top and foam I found both bulkheads were bad, part of the main stringer and the plywood on the inboard side of each center board housing (boat has two). After doing alot of research I decided that I would epoxy coat all the plywood to provide the best waterproofing. Some of the ply needed to be glued together to get the correct thickness anyway. So far I have the new stringer piece, one of the bulkheads, and both plies for the centerboards coated on both sides. My original plan was to tab, glass over the floor and centerboard sides with polyester and CSM to save costs. I also planned on gel coating the floor to give a nice appearance and somewhat of an anti slip to it. I though it would be best to apply gel coat to polyester. Fortunately I would be short of epoxy and called my supplier for more. After some discussion he informed me that putting polyester over epoxy is bad. Other way around is ok. So taking this into account I can switch to epoxy and fabric to tab the stringer and bulkhead in place. My problem is if I apply fabric and epoxy to glass the centerboard pieces it would force me to tab the floor to epoxy at these points and where the floor meets the bulkheads. The floor fits right between the center boards and the two bulkheads. My question is would it be ok to do this in these areas? I sailed it a few times without the floor even there (foam only) and it seems pretty strong. I hate to epoxy the whole thing because I have 3 gallons of resin, plus gel coat shouldn't go over polyester. I could scrap the wood and work and start over with all polyester, but it sounds like that isn’t the best way to water proof plywood. I feel like I am in a conundrum.

 

There are basicly 3 resin systems
polyester is the bottom of the ladder !!
then Vinylester resin it a lot better than poly and is a tough resin it will go over ply without to many problems and at a pinch poly over vinylester but not for major srtuctual, stuff .
Epoxy will go over both but neither of the other 2 should be used over epoxy as it dosent stuck very well and if you gel coat over epoxy it could possibly not go hard or if it does go hard wont stick very well and could simply peel off some time later .
There is nothing wrong with using poly to seal your wood just give it a good 2 or 3 coats then poly the rest and flow coat over to get a good finish .
stay with one system and dont try mixing the others because they may not match !!.

 

Poly doesn't seal wood. Vinylester is better at sealing wood, but still not truly waterproof. Epoxy is capable of sealing wood.

You can gel coat over epoxy, though you'll need a tie coat, to improve adhesion.

Tunnels and your supplier are correct, polyester doesn't stick well to epoxy, though it does stick to some degree.

As to your structural concerns, it's difficult to tell without some pictures. As Tunnels mentioned, it's usually best to stick with a single resin system.

 

dont try to mix and match !! usually dosent work well !!

Just remember when you resin coat plywood the resin only soaks to the glues line its mainly edges where water gets in and soaks up the woods grain . so resin coat and soak and pay special attention to the edges 3 ply the sealer will soak into the veneers 5 and 7 ply its the edges and ends as the veneers are thinner so the resin doesnt soak in very far !!

 

Thanks for the replies. One part I didn’t describe well is the deck sat on two 1x2’s that went the full length bow to stern. The 1x2’s look like there were more less spacers to raise the deck up. They were not glassed in on their own and there wasn’t any screws in them. They were square to the deck and not the hull. They must have been glued to the deck and installed in one piece before the foam was installed, because there was foam partially underneath them. These 1x2’s and deck sit right next to and touch the centerboard housings. The stern end of the deck buts up to the bulkhead. The bow end goes under the other bulkhead and goes all the way to front. The deck was glassed to the hull, to the bulkheads and the centerboard housings. In theory the deck is enclosed on all sides and becomes watertight.

Based on your replies I think the only solution is to start over and stick to poly and live with reduced water resistance (first go around lasted 30+ years). I’d send a picture but my boys decided to play catch with the camera the other day.

 

Some epoxies you CAN put polyester on top since they are designed for that.

http://www.systemthree.com/store/pc/SB-112-c12.htm

 

Many epoxies are suitable for at least accepting a topcoat, without any problems.