Fiberglass repair question

[matty377]

Hi-

I'm new here, so if I'm asking the wrong questions in the wrong place, let me know.

I'm (attempting) restoring my father's old 1968 Glastron GT-160 and I have 3 holes in the hull I need to fix. One isn't all the way through and the other two are actually straight/clean cuts rather than holes, so they are less than 1/8" wide, probably more like 1/16". One of the cuts is about 18" long and the other is about 2".

From what I've read, when patching holes in fiberglass you should cut out more than the actual damage, taper the hole, insert backing, and create a layered fiberglass patch. I've also seen some other suggestions for smaller holes that don't require cutting larger holes (epoxy, marine tex?, etc..).

My question is: When is the hole too large to be patched with these filler products and when is it absolutely necessary to replace sections of damaged hull with full fiberglass patches? I'm just looking to get this done the right way.

Thanks for your help.

-Matt

 

[oops!]

Re: Fiberglass repair question

cutting the hull is never the answer to a patch.

all you want to do is grind the area around the hole...that way the layers of glass have somthing to grab on to.

slices can be patched from the inside and not the outside......
if you can match the color of the gellcoat...placer a thick piece of plastic over the slice from the outside.....and tape it firmly in place.

fill hole with structural gellcoat....cover from inside with a few layers of glass.

 

[matty377]

Re: Fiberglass repair question

Hi-

Thanks for the reply. I'm guessing the structural gelcoat is thin enough to fill in the slice. Should it fill the entire depth of the slice or just the thickness of the "factory" gelcoat? And then fiberglass right over the slice from the inside?

Thanks again. This is very helpful.

-Matt

PS - What's "structural" gelcoat?

 

[duners88]

Re: Fiberglass repair question

You want to try to get a thickness of Gelcoat about as thick as factory.

The method that oops! described is very similar to the way the boat hull would have been made at the factory. The hull mold is sprayed with Gelcoat then glass layers are built up behind/inside the gelcoat.

To answer your question about "structural" gelcoat:

Gelcoat and resin cure through a chemical reaction between it and a catalyst. This reaction creates an exothermic (meaning it gives off heat) reaction. Structural or Layup resins and gelcoats will not cure "hard" exposed to air(I think it might actually be oxygen but don't quote me on that), they remain a little tacky. This is so that the next layer can create a stronger bond. A "finish" resin or Gelcoat contains a wax that melts during the exothermic reaction and seals the surface from air exposure and it cures "hard" (meaning you can sand/paint/finish it). If you wanted to add another layer to a "finish" coat you would need to remove the wax (usually by sanding or grinding) and expose the resin in order to get a good bond.

In the process that oops! gave you the reason you don't need to use "finish" gelcoat is that the plastic that you place on the outside of the hull will seal it from being exposed to air and it will cure hard. While the surface of the gelcoat on the inside of the hull will remain tacky allowing you to build up the fiberglass and create a strong bond with the gelcoat.

The last layer of fiberglass that you lay in the patch will need to use "finish" resin.

The only thing that makes "finish" differ from "structural"/"layup" resin is the addition of wax.

If my explanation is off please correct me.

-Duane.

 

[matty377]

Re: Fiberglass repair question

Thank you both for the info. You guys are awesome!