Using poly resin without glass

[Jim Hawkins]

I have a piece of plywood decking I made for a boat I'm working on. I want to cover it with glass eventually but in the meantime while I'm working on the boat and making adjustments, I just want to waterproof it while I test the boat and fit things.
I thought I might just mix up some resin and give it a coat without glass just to seal it and when I'm satisfied with my plan sand it and finish it with glass.
Nuttin wrong with that, right?

 

[Pmt133]

I will preface this with the fact that I am not a professional and this is just based on what I've read and seen others do any my own limited experience working with the stuff...

I don't see a major issue with it... I would just do a so called "primer" coat.... The only issue I think you can run into is if you're using an unwaxed poly resin, your deck will stay tacky if you have it in place and are walking around on it. My boat was in a garage so glassing the deck was one of the last things I did so I was just walking on bare plywood instead of the resin grabbing everything on my boots or suit. The other issue I had was the deck needed to be finished to build the side boxes as they bonded on the finished deck. So compromises were made.

I would mix up a batch with the lower end of MEKP recommended and roll it on light and then rough sand like you said when ready to glass. Some people like to thin with styrene for a true primer coat...

 

[88 Capri (2022 SOTY)]

I used 2 coats of resin on bare wood because one coat will soak in quite a bit, I wiped generously with acetone before the first coat and in between the 2.

 

[Drivewayboater2]

Agree with capri…. 2 coats. Depending on type of wood you are using it’s gonna soak in pretty good. I did light sanding and acetone in between coats.
I coated all wood when doing my seat rebuilding. I wanted to be sure the wood would last underneath the seat cushions.

 

[Jim Hawkins]

Great, Thanks!!

 

[Jim Hawkins]

I'm wondering, since the plywood is covered in resin, how long would it hold up applying gelcoat without glass? I'm sure it's been done the question is would it hold up? Anyone out there actually do this?

 

[Scott Danforth]

They used to slap gel coat over plywood in the 70s and 80s...... Basically all the rotten boats

It's not a good idea

Now, cover the plywood with 1.5 oz cloth, make smooth, sand smoother, apply gel, polish. It will last a fair amount longer

 

[Chris1956]

Jim, you can think of poly resin w/o cloth as a good varnish. It will seal wood quite well. Of course like varnish, it will not bridge seams in the wood. So if you were to build a kayak of wood and seal it with poly resin, it would work fine, until the wood flexed and a joint opened a bit. Then you would take on water.

 

[JKLknik]

Polyester Resin is NOT waterproof.
Pine is not a great timber to get wet.
For the few dollars on such a small project, I know what I would recommend.

 

[cyclops222]

DO the wood correctly. The first and only time.

 

[todhunter]

Yeah, the bulkhead at the front of the bilge in my boat (built in 1987) was plywood with gelcoat and no cloth. When I got the boat you could poke your finger through it.

 

[cyclops222]

You have a project boat for sure. Good Luck

 

[Jim Hawkins]

okokok, I'll glass. Can I gelcoat on top of tacky resin and fiberglass?
?

 

[Pmt133]

Use unwaxed resin, let it set then gelcoat with a coat of unwaxed then a coat of waxed. That's how I did my bilge and electronics area.

I wouldn't gel over wet resin/glass only because you may shift something/cause an air bubble and you might not see it.

 

[Chris1956]

Jim, there are two kinds of poly resin. Laminating resin (no wax) stays tacky after it sets. Finishing resin (with wax) gets rock hard. You can gelcoat over either, but sanding the finish resin is recommended.

The gelcoat also comes in waxed and unwaxed. Unwaxed is used for the first coat, if you plan a second coat. A piece of saran wrap over the unwaxed gelcoat will help it cure to rock hard.