Gel coating on interior surfaces?

[chowdan]

Curious if anyone has any experience with this?

Some of you may know i've been slowly rebuilding interior of my boat. Most of the wood i've pulled I replaced with painted wood, however part of the settee that i'm rebuilding I decided to test out a gelcoat job.

I decided that since this is an area thats covered mostly with cushions, if the gel coat cracks/looks like ****, then well I'll redo it eventually with paint regardless if i have to sand it all off.

I'm curious if anyone has applied gel coat over cabinetry? The plywood was covered in fiberglass and polyester and gel coat applied over that. Wondering if modern boats just gelcoat all their pieces before installing inside?

PS - only reason I'm doing it is because I have a ton of left over white gel coat, so figured since it's never going to get used, might as well attempt to use it.

[Spot]

My limited experience shows both PE and epoxy resin developing cracks from the movement of the underlying plywood when used without fiberglass cloth. These were both exterior applications in a full freeze-thaw climate (Minnesota). I would expect an interior done somewhere milder to be more robust. Is the resin waxed?

[tkeithlu]

As Spot suggests, you are asking for thermal expansion and moisture expansion problems. Gelcoat over fiberglass is basically the same stuff minus the cloth. They expand and contract together. Gelcoat over wood is two completely different responses to temperature and humidity. I could see it working if you put down a layer of cloth first as a base for the gelcoat.

[Chotu]

Originally Posted by chowdan

Curious if anyone has any experience with this?

Some of you may know i've been slowly rebuilding interior of my boat. Most of the wood i've pulled I replaced with painted wood, however part of the settee that i'm rebuilding I decided to test out a gelcoat job.

I decided that since this is an area thats covered mostly with cushions, if the gel coat cracks/looks like ****, then well I'll redo it eventually with paint regardless if i have to sand it all off.

I'm curious if anyone has applied gel coat over cabinetry? The plywood was covered in fiberglass and polyester and gel coat applied over that. Wondering if modern boats just gelcoat all their pieces before installing inside?

PS - only reason I'm doing it is because I have a ton of left over white gel coat, so figured since it's never going to get used, might as well attempt to use it.

No good. Don’t even waste your time on that.

IF you got it to stay on the wood (by first sealing the wood with epoxy or potentially polyester resin), you’d have the worst sanding job of your life ahead of you to get it looking good.

Gel coat is meant to be used in a mold. That’s what the modern boats are doing. They have a perfectly smooth and polished female mold for interior parts with a mirror-like surface. They apply PVA mold release to that mirror like surface, then apply gel coat, then fiberglass. That’s why they look good. When they are popped out of the mold, the gel coat takes on the mirror shine from the perfect mold.

You putting gel coat on stuff will not work like that. It’ll be a splotchy, lumpy mess and you’ll have to sand it smooth, then work through all the grits of sand paper all the way up to 65,000 grit to get a shine. Then polish it. It’ll take many days. Gel coat does not sand well at all.

Paint it.

If you want a shortcut to a beautiful finish, do what I did and what a lot of new boats do. Formica.

[Chotu]

Formica example from my shower compartment.

[ggray]

Originally Posted by Chotu

Formica example from my shower compartment.

Very nice!

How did you make that corner look so good?

[gonesail]

paint can be a really nice finish. if I didn't have such beautiful varnished teak .. I would like to paint it. formica very nice too. white is bright and cheerful down below.

[Chotu]

Originally Posted by ggray

Very nice!

How did you make that corner look so good?

It’s a shower, so that’s silicone caulking. Has to be completely water and steam proof.

[Cadence]

Originally Posted by tkeithlu

As Spot suggests, you are asking for thermal expansion and moisture expansion problems. Gelcoat over fiberglass is basically the same stuff minus the cloth. They expand and contract together. Gelcoat over wood is two completely different responses to temperature and humidity. I could see it working if you put down a layer of cloth first as a base for the gelcoat.

I believe he said the wood was glass and polyester covered. I wouldn't think the gelcoat would be a problem. My concern would be polyester to wood bond unless the wood had been saturated with acetone thinned polyester.

[bcboomer]

Gell coat is often used on exterior repairs and recoats instead of painting so I don't see why it couldn't give a nice finish.

[Cheechako]

I think gel may crack on anything very flexible or that expands/contracts like wood. It does flex some on hulls etc though. It has been sprayed heavily inside cabinets on boats many times (glass and tabbed on wood) so it may work. I agree to coat the wood with resin first for a good bond.

[KadeyKrogen38]

Simple answer. BAD IDEA!

[chowdan]

Well i'm glad everyone is saying this a bad idea, because it's already done, so the experiment has been started regardless!

That said, the wood was saturated in thin polyester first, cured, sanded, wiped and then polyester coated with a layer of glass over it, so hopefully that will hold structure. As for flexible, well only time will tell to see how flexible this really is and how it holds up over time.

If we do get cracks in the gelcoat, well the good news is the plywood wont have delaminated and it'll be easy to remove from the boat and route out a new piece which i can saturate with epoxy and paint(which is what i typically would do). Sure does add some effort, but it's i guess an "experiment now"


I'll be doing some wet sanding over the next few evenings to see how it turns out

[chowdan]

Originally Posted by Chotu

No good. Don’t even waste your time on that.

IF you got it to stay on the wood (by first sealing the wood with epoxy or potentially polyester resin), you’d have the worst sanding job of your life ahead of you to get it looking good.

I'm curious why this would be the worst sanding job of my life? I've grinded hundreds of sqft of fiberglass, thousands of sqft of bottom paint in my life, surely sanding down these pieces can't be that bad?

As i said before, if they fail and crack all over, i'll just pull them out, use them as templates and remake the pieces down the road. Maybe in 5 or 10 years i'll do it, but structurally they will be in better shape than the ply that was pulled from the boat, just cosmetically at that point they may look like ****.

The settee top literally had every layer delaminated and was basically unsound. To replicated the pieces I had to mark where the layers lined up to survive the journey to the shop.

[Cheechako]

Originally Posted by chowdan

Well i'm glad everyone is saying this a bad idea, because it's already done, so the experiment has been started regardless!

That said, the wood was saturated in thin polyester first, cured, sanded, wiped and then polyester coated with a layer of glass over it, so hopefully that will hold structure. As for flexible, well only time will tell to see how flexible this really is and how it holds up over time.

If we do get cracks in the gelcoat, well the good news is the plywood wont have delaminated and it'll be easy to remove from the boat and route out a new piece which i can saturate with epoxy and paint(which is what i typically would do). Sure does add some effort, but it's i guess an "experiment now"


I'll be doing some wet sanding over the next few evenings to see how it turns out

Cool, did you spray o r brush?
The entire cabin and deck was redone by a pro on the boat in my avatar with good results. Spray and polish. Not that lumpy or impossible to do for a pro.

I also did spots on the cowling at the companionway on my home finished 31 footer. I had made tunnels through the cowling for lines led aft while building that boat. The spray (airless sprayer) was a bit rough but polished smooth readily.

Neither was as hard as indicated by others above.