is fiberglass waterproof?

[lingcod]

I am working with a polyester resin in building a new motor well. I have been told that cured resin is not waterproof. my neighbor told me that is why they put gel coat on a boat. is he right? personally i dont see how water can get through cured resin but he's got me thinkin'. any input is welcome. I hope i'm right here cuz my neighbor is getting on my nerves and i want to shut him up.<br /><br />lingcod

 

[ED21]

Re: is fiberglass waterproof?

Gel coat is not completely waterproof either. Ask anybody that has had a boat bottom blister.<br />The cured resin should be protected from UV with paint or gel coat to keep it from deteriorating.<br />If it's not under the waterline, I don't see a problem other than appearance if it's not gel coated.

 

[one more cast]

Re: is fiberglass waterproof?

From the duroplastic web site. <br />

Gelcoats are specially formulated polyester resins with a flexible additive to improve the impact resistance against cracking and to produce a tough, resilient film on the surface.

So, gelcoat is resin.

 

[lingcod]

Re: is fiberglass waterproof?

it is not underwater but it will be in contact with water alot. this boat has a very lowcut transom. water is constantly coming in and out of the back. any way to make it waterproof?<br /><br />lingcod

 

[Terry H]

Re: is fiberglass waterproof?

lingcodjamie, it's a stretch to say it's not waterproof, but a case can be made since there is such a thing as blisters. I wouldn't even worry about it, properly built it will expel water, and properly primed and painted it will handle the uv. Chief

 

[lingcod]

Re: is fiberglass waterproof?

thanks guys, I guess that pesky neighbor of mine is kind of right.I aint tellin him. as soon as the sun comes out I'll finish this project. kind of hard to work with resin when it's only 53 degrees outside.<br /><br />lingcod

 

[jim dozier]

Re: is fiberglass waterproof?

Nothing is waterproof there are just varying grades of waterresistant. Polyester resins (including gel coat which is basically polyester resin with color and waxes) are pretty good but not as good as epoxy. Also when working with wood epoxy bonds better to wood than polyester. Epoxy is also more flexible than polyester which is another reason it works better with wood. Boats are usually built out of polyester resin because it has adequate moisture impermeability, is less expensive, and easier to work with in production lines. High end composites for boats, race cars, and airplanes are usually made out of epoxy because it is stronger and has a higher bond strength. If you are patching polyester resin you can probably just use polyester resin. If you are working with wood and polyester I would go with epoxy.

 

[crab bait]

Re: is fiberglass waterproof?

poly is not waterproof.. an lets rot causing spores go thru like a sive..<br /><br />also,, it's not a glue.. an does not truly bond to wood in the long run..

 

[flashback]

Re: is fiberglass waterproof?

no

 

[Bondo]

Re: is fiberglass waterproof?

On the Molecular Level,....... Your neighbor is Right.............<br /><br />On a Practical Level,... Fiberglass is Very Water-Resistent,.... And, With a coat of Good Paint,.. It's Very Waterproof...........<br /><br />No Doubt,... Epoxy Is Better......

 

[lingcod]

Re: is fiberglass waterproof?

all right. I think i got it. epoxy is better. heres the problem. I've already got 1 coat of glass and poly resin on the motor well. can I recoat with epoxy to help seal? I want to do this right but please don't tell me to sand to wood and start over, I will if I have to but sure would like an easier alternative.<br /><br />lingcod

 

[Realgun]

Re: is fiberglass waterproof?

Actually you can put epoxy on poly but not poly on Epoxy. <br /><br />You will want to scuff the poly a we bit to give the epoxy some bite. Just get a sanding sponge mediam grade or sand paper about 120-240 and just graze the surface. Wipe clean some people same use some solvent I sat water is fine just ve sure its dry before you lay the Epoxy. You will need to paint the epoxy to give it some UV resistance or in 5 monthes it will be yellow and start to become brittle.

 

[lingcod]

Re: is fiberglass waterproof?

sweet! music to my ears. thanks for all the advise guys<br /><br />lingcod

 

[crab bait]

Re: is fiberglass waterproof?

yeah, but usin' the poly you saved a few bucks..!!! isn't that great..!!

 

[flashback]

Re: is fiberglass waterproof?

You could paint it with several coats of barrier paint (interlux interprotect) then a couple of coats of topside paint to protect the barrier paint from sunlight..kinda like real gun said

 

[captaindarian]

Re: is fiberglass waterproof?

JUST PUT GELCOAT TINT IN EPOXY RESIN and your waterproof. There are lots of colors of tint for gelcoat that work great with epoxy. Epoxy is waterproof.

 

[Bondo]

Re: is fiberglass waterproof?

Epoxy Is in fact very Waterproof,....... But has No UV Protection........<br /><br />Painting Over it is Better than Tinting......

 

[lingcod]

Re: is fiberglass waterproof?

with a little backtracking my motor well is almost finished. sanded down the poly to almost nothing, recovered with 2 coats of epoxy. then coated with one coat of glu-vit. my heater quit working one night and the glu-vit sagged. trying to sand but what a pain. this stuff clogges the paper like trying to sand wet silicone. hope to be painting this week. thanks for all the advice guys.<br /><br />lingcod