Repairing bigger fibreglass holes... - Fiberglass RV


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Old 07-16-2018, 10:35 AM   #1
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Name: Rob
Trailer: Boler
British Columbia
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Repairing bigger fibreglass holes...

Hi Everyone,

I've reviewed a number of the threads on here about doing fibreglass repairs and I have the basics down, but have one specific question.

I'm going to be attempting to fill in the larger holes from where the furnace and other appliances vented through (3 holes, biggest is about 12" square). Every thread I have seen so far suggests using a scrap piece of fibreglass to fill the hole and then use mat/resin to join it to the existing wall.

My question is, how do I do this if I dont have spare fibreglass? Is there a limit to the size of hole you can fill by simply using the fibre mat and new resin?

Any help here would be appreciated.

Thanks,
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Old 07-16-2018, 10:47 AM   #2
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Rob, although I am not an expert, i have worked with fiberglass with other projects. You can fill any size hole with the fiberglass mat, what i would be concerned with is putting some type of backing in so that the fiberglass can be close to the shape/contour of the camper and the area you are filling. Once you put in a backer you can keep adding layers of mat to get to the desired thickness. I have used something as simple as cardboard covered with aluminum foil as a backer.
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Old 07-16-2018, 10:53 AM   #3
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Trailer: Boler
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Thanks Dave, that is helpful. Pretty much what I figured, but wanted to be sure. In your experience can I work on filling a hole that big if the area to be filled is vertical? Or do I need to put the trailer on it's side so the area is flat?

Sorry for the noob question, not sure how much the wet resin will "run".... hope that makes sense.
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Old 07-16-2018, 11:04 AM   #4
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You can work on it in the vertical position, just be aware that the fiberglass resin will drip, so protect the area you are working on. You can also mix the resin a little hot with extra hardener, your work time will be much shorter but it will set faster and be less of a runny consistency. People also sometimes mix in shredded pieces of fiberglass mat to kind of thicken up the resin.

I would also pay attention to the mat/cloth while its setting because sometimes in the vertical position it will want to slide down. You may have to physically push it up back into position until the resin starts to set.
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Old 07-17-2018, 06:35 AM   #5
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I turned a large sunroof hole in the roof of my old boler into a small vent hole. Cut a piece of birch plywood an inch larger then the hole. Jammed it in place with a 2x4. Glassed in the hole with layers of mat and resin until it reached the thickness to match the roof. Sanded and used body filler to smooth it out then primed and painted. Since I didn't have a piece of ensolite to fill in the interior to match the roof I left the birch plywood on cut the hole for the vent and bolted it in. If you want to remove the plywood form cover it with waxed paper.
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Old 07-17-2018, 08:04 AM   #6
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Originally Posted by RobK View Post
Hi Everyone,

My question is, how do I do this if I dont have spare fibreglass? Is there a limit to the size of hole you can fill by simply using the fibre mat and new resin?

Any help here would be appreciated.

Thanks,
Here in the USA, a quick trip or two to a Habitat for Humanity Restore would be my recommendation. Find a bathtub surround. Advantage of using a piece is if you are patching a flat larger hole, its going to be nice and flat.
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Old 07-17-2018, 09:30 AM   #7
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Name: stephen
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Originally Posted by RobK View Post
Hi Everyone,

I've reviewed a number of the threads on here about doing fibreglass repairs and I have the basics down, but have one specific question.

I'm going to be attempting to fill in the larger holes from where the furnace and other appliances vented through (3 holes, biggest is about 12" square). Every thread I have seen so far suggests using a scrap piece of fibreglass to fill the hole and then use mat/resin to join it to the existing wall.

My question is, how do I do this if I dont have spare fibreglass? Is there a limit to the size of hole you can fill by simply using the fibre mat and new resin?

Any help here would be appreciated.

Thanks,
After using 2 layers of mat or cloth, consider using a structural as biaxal, as mat is not structural, filler.
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Old 07-17-2018, 09:44 AM   #8
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After using 2 layers of mat or cloth, consider using a structural as biaxal, as mat is not structural, filler.

I don't claim to be any kind of expert, but since many of the classic trailers, (Boler, Trillium, and others) are constructed using a fiberglass chopper gun, which as far as I can tell produces essentially a mat type of fiberglass arraignment, I don't see how you can say it is not structural.
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Old 07-17-2018, 09:53 AM   #9
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There's at least one "thixotropic" filler out there - West Systems - and I expect there are others. You mix your resin and hardener (and when using the filler, I've had better results with a slower-curing resin - and NOT fiddling with the resin/hardener ratio) and then start adding the filler. When you mix in the filler, the resin starts to get a consistency about like mayonnaise. More filler and it gets like peanut butter - either will hold in place on a vertical surface.

On horizontal surfaces, I've used powdered limestone from the garden center. But that won't stay on a vertical.

I've mentioned this before but it's worth a repeat - the folks at West Systems (Gougeon Bros.) have a lot of free information on how to go about working with their stuff. One thing they recommend - and before I tried it, I didn't believe it - is to grind away the edges around the repair site to a ridiculous amount, and then lay on one piece of glass, lots bigger than the hole, but a little bit smaller than the "scarf". So then you have a backup that's bonded to a LOT of surface, and you can fill in the rest of the space with progressively-smaller patches. Sounds complicated, but if you get the West info, it's clearly explained.

EDIT FOR CLARIFICATION: Yes, you CAN change the pot life for POLYESTER resins by adjusting the ratio of hardener. But that doesn't work for EPOXY resins, which are what I've used for the past few decades. Fiddling with the ratio for epoxies will only get you a weaker bond.

Mandatory disclaimer - I have no connection, either personal, financial, or professional with West Systems or Gougeon Bros. I'm just a satisfied user of their products.
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Old 07-17-2018, 09:58 AM   #10
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When I wanted a larger piece, I laid some wax paper on a table, then made a thin flat piece that would fit into the hole. I cut it square (I was going to use it as a cover) and it was stiff and stayed in place. I think you could do much the same thing, using a couple of mats and less epoxy, that would then be able to be placed where you want it.
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Old 07-17-2018, 12:56 PM   #11
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. I have used something as simple as cardboard as a backer.
Reminds me of using an Aunt Jemima pancake box to repair a damaged canoe on our 9 day wilderness trip through our Pukaskwa National Park back in 1980. Sure glad we took FG mat and resin on that one.
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Old 07-17-2018, 03:16 PM   #12
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Name: Rob
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When I wanted a larger piece, I laid some wax paper on a table, then made a thin flat piece that would fit into the hole. I cut it square (I was going to use it as a cover) and it was stiff and stayed in place. I think you could do much the same thing, using a couple of mats and less epoxy, that would then be able to be placed where you want it.
Great idea Eric, thanks. If I can't find a piece of scrap FG as suggested above I will likely go that route. Cheers.
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Old 07-17-2018, 04:09 PM   #13
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This may sound funny, but you can use plywood to basically fill the hole, too, and then fiberglass over it. I'd use ply that was quite thin, and I might wish for exterior ply, but it can be done. I'd hold it in place with blue masking tape (the kind that doesn't leave a big residue) and then leave an area all around it to fill with more solid glass and mat/cloth. I'd layer cloth and mat alternately to get strength from both, and I'd use a backing (waxed paper over cardboard works fine). If you go this route, you will have to glass over BOTH sides of the ply! But you probably figured that out anyway.


Best luck to you, a project can be so fun and rewarding! May it come out well and may you have safe travels and much enjoyment.


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Old 07-17-2018, 04:10 PM   #14
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Rob,

Go to the other side of the trailer and make a mold of the opposite area you want to fill. Make it a couple of inches larger than your hole. Then place that temporary mold over the actual hole after coating it with a mold release agent or wax or plastic wrap, and tape it on. Then fill in from the inside with glass mat and resin.

Before you place the new mold over the hole, sand the edges of the hole to a fine taper and clean fiberglass.

Remove the temporary mold, fill imperfections, sand and paint. The surface will be almost smooth enough from the surface of the mold that was laid up on the other side. It will also have a subtle curve to match the contour of the body. The tapered edge avoids a "butt" joint and allows the glass to overlap. With some careful sanding and a bit of filling, the hole will disappear and be just as strong as the rest of the body.

If there are any cracks or fractured areas, you can use Smith epoxy to coat those areas first. This is very thin and sets slow to wick into damaged areas and give you something to get ahold of. I like using epoxy to repair or remodel polyester resin fiberglass structures. System Three or West Systems are available and good stuff. Fairing small areas can be done easily with Marine-Tex, which is like a white putty when mixed.
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