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jephotog 06-15-2019 01:37 PM

Need fiberglass help
My locker got damaged from an anchor bouncing around on the road, so that hole needs repairing. Also there is a hole to accommodate the scupper drain that I'd like to patch over. Since it's been a while since I have done fiberglass work just wanted to double check before starting.

The fiberglass is not very thick so I am not able to taper much, also since this is not a structural component I was thinking of just putting a piece of fiberglass cloth over each hole then coming back with matt to fill in the concave sections created.

Is there a better way to go about this?

Would polyester resin do okay here or should I use West Systems epoxy?

Cassidy 06-15-2019 04:34 PM

Re: Need fiberglass help
In my experience polyester resin doesnít stick well to old polyester. I would definitely use epoxy of some sort and the West System product is my standard go-to. The simplicity of their 105/205 product with the calibrated pumps is hard to beat. Use 206 (slow) hardener for jobs likely to take more time.

krisscross 06-15-2019 08:25 PM

Re: Need fiberglass help
IMO west system epoxy is really superior and thatís what I would use. Clean the surfaces really good and wipe with acetone. Use thickener when working with holes and vertical surfaces. I like to use silica, also from West system. Overlap the repair area with cloth. I prefer the woven fabric. Make sure itís saturated with resin and no air bubbles.

BillMoran 06-16-2019 12:11 PM

Re: Need fiberglass help
I read an article recently where they tested the strength of epoxy vs. poly resin; and the expoxy resin was hands down stronger in secondary bonding (i.e. it sticks better to old stuff). Given that it's not a structural repair, that may not be that important, but since you'll have difficulty getting a large taper, it might actually be an important consideration.

As far as the rest of the plan. My experience is the best way is to make a thin sheet of fiberglass (like, 1 layer of glass fabric + resin) and once that's hard, cut it to shape and use thickened epoxy to attach it to the back side of the hole. Then add layers of cloth on the front till you're almost up to height. Wait for that to cure. If it seems strong enough, then move on to fairing and painting. If it seems flimsy, then add layers of glass to the back side until it's strong enough ... then fair and paint. Of course, that takes longer than doing it all in one go, but as a beginner, it gives me a lot of leeway to make mistakes and recover from them.

TQA 06-16-2019 12:15 PM

Re: Need fiberglass help
Epoxy is much better IMHO. I use West. Their web site has many hints and tips and step by step guides.

Most chopped strand mat does not work with epoxy if planning to use CSM get the stuff that does work with epoxy.

If the surface finish matters learn how to use peel ply. IT IS MAGIC STUFF.

If it is not structural then any kind of tapered edges work , do both sides if possible.

If using a filler to thicken the epoxy micro balloons will sand easily silica will not.

Remember if you **** up totally it is no big deal just grind it off and do it again.

jephotog 06-16-2019 01:02 PM

Re: Need fiberglass help
Well I was watching a video from Boatworks today and he was using polyester resin, and then was also showing how to gelcoat. I figured it would be a good place to practice his techniques. I was aiming to use the poly resin but when I opened it the whole can was cured rock hard. So hear double checking my west systems approach. All my stuff is so old the hardener looks like molasses.

jephotog 06-16-2019 04:50 PM

Re: Need fiberglass help
1 Attachment(s)
First coat has been drying a few hours. I used West Systems slow hardener. Do I have to wait overnight to then scuff up to add the other layers or can I add them now?

TQA 06-16-2019 04:53 PM

Re: Need fiberglass help
You can add extra layers now. In fact it is better as the new epoxy crosslinks with the stuff you have applied as long as it is green.

colemj 06-16-2019 08:26 PM

Re: Need fiberglass help
Tapering depends on thickness. A thinner section requires a smaller dimensional taper, even though the taper ratio is the same. Usually with thin glass, a sander will work well for tapering.

I don't have any issue with polyester on repairs like that, but the repair is so small that the difference in cost is minimal and the difference in properties isn't a concern. If you need to gelcoat over it, this is still possible with epoxy. Just key it up well before gelcoating because you will be relying on a mechanical bond rather than chemical. I've had good results with gelcoat over epoxy.


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