Vynil ester with plywood

Thank you for the information!!!

 

I have never seen anyone use any kind of "paint" for a binding agent between wood and Polyester or Vinylester before.

How great is the cost differential between epoxy and Vinylester in your country?

Here I remember 25 years ago it was something like $29 for poly and $89 for epoxy so I used poly for small boats and a deck I built. It worked or I should say it didn't fall apart under the use I put them to which wasn't heavy.
Now everything has gone up, but epoxy has actually gone down in price. With the cost of marine plywood nowadays it doesn't make sense to use anything but epoxy here.

 

Here in my country the price of ethylene-vinyl and epoxy is about the same. It is 15-20 euros an kg. But structures have changed. Place timber on transom and only at certain points in the deck. The reason is that the wood rot and have problems. All the beams is a polyester and one with the hull, thereby ensuring longer life and greater rigidity

 

Tunnels, FYI, DB1708 is NOT 0/90, it is 45/45 with a .75oz mat which is exactly what one should use for tabbing in and ideally for all the seams on stitch and tape although with most small boats its obviously not neccesary,actually DB1700 is better with epoxy,no need for the mat. Im not disputing that epoxy is the better choice when tabbing in wood, just that its not the only choice and im sure you know that epoxy does not penetrate any significant amount into the plywood on face grain,it is a surface coating and that is fine so no i see no reason to downgrade to 3 ply. I must say it kinda suprises me that you are such a proponent of epoxy for everything being a Kiwi. When i started boatbuilding in NZ in the early 70s we used what was appropriate for the task at hand and it wasnt always epoxy, even though it had been in common use since probably the 50s so it was just one of the arrows in the quiver, on cold molded boats we laminated frames,stem,floors,transom,deck beams and did our scarfs with resorcinal, glued stringers to the frames and the first diagonal skin to the stringers stem and backbone and transom with epoxy and laminated the skin with resorcinal,sheathed with dynel or glass cloth with epoxy,most interior gluing was done with either epoxy or Aerolite UF glue, it wasnt until i came to the US where epoxy was a newer thing in boatbuilding where i encountered the one size fits all, epoxy for everything mentality.
Steve.

 

In my opinion the polyester I'm working with has a weak bond to wood. Can someone tell me what you guys would consider proper usage like gonzo speaks of in a rather large repair using polyester and wood?

 

What are you trying to bond?

 

Bulk heads (4- ply) plywood and stringers (spf 2x4s) in 2-32' pontoons off a catamaran cruiser. They had water intrusion from the top side and we had to hull them out. I have someone helping me from a fiberglass shop but I do not feel as if his is soaking the resin into the wood properly.

 

Normally, you brush on a thick coat of resin first. Then the fabric gets laid on top and wetted. A combination of plastic spreader and metal roller is used to get the air bubbles out. What makes you think he is not soaking the resin properly; are there voids and bubbles?

 

No, that is pretty much what he is doing. A lot of what I have read stated to thin the resin down with styrene and coat the wood before actually doing the layups to allow better penetration. When we started last weekend I questioned that with him and he said there was no need for it. We glassed a small piece of plywood at the end of the day just so I could check the adhesion. Last night I was able to pull the glass off by hand without a ton of effort, so then I started questioning the adhesion in general.

 

Did you try to pull it off the same day? That wouldn't give it enough time to cure.

 

No, it was 3 days later. I'm thinking I just had a really strong moment, plus I started from the corners. After all, anytime I have ever removed glass from wood a cut wheel and a good chisel has always been required. I have worked on several boats from the 80s which I am sure just had GP polyester. More or less I think I was concerned him not thinning and soaking the resin into the wood. I have never tested it so I really don't know if it helps adhesion or not.

 

Thinning the resin is normally a bad thing, you reduce the physical properties quickly, the more you add the weaker it gets.

Apply some resin and allow it to soak in and let it become at least somewhat hard before laying down any glass on the surface, this should increase the bond a great deal.