This Instructable comes from a recent project I have been working on that involves fixing up an old fiberglass travel trailer. In the remodeling of this trailer, I was left with many small holes from antiquated peripherals on the sides of the trailer (like a phone jack). There was also a six inch crack in the front from a rock hitting it on the road.

I actively searched for the best way to patch small holes in fiberglass on the web, and couldn't quite find concise answers - this lead to a more dedicated search. I ended up talking to surfers, sailors, and prop-masters about how they make repairs to structual fiberglass and came up with the following methodology.

Hope this is helpful, and I would love to hear back from the community on this.

Step 1: Materials and Tools

DISCLAIMER: Working with Fiberglass is rough. It is nasty nasty stuff, and can get into your skin, your lungs, and your eyes. When working with these materials it is important to wear a respirator, gloves, and safety glasses. It is advised that you wear a paint suit to cover all skin that could be exposed to fiberglass particulate.

I got a bulk of my materials from Douglas and Sturgess in Richmond, CA - the folks at the store were incredibly helpful and super nice! THANK YOU!

Materials: Tools:
  • Small Disposable Paintbrush
  • Angle Grinder with Grinding Disc
  • Orbital Sander with 80 Grit Disc
Odds and Ends:
  • Stir Sticks
  • Respirator
  • Gloves
  • Safety Glasses
  • Permanent Marker
  • Duct Tape
  • Rags
<p>Wd40 works as a very effective releasing agent, if you don't want the resin to stick to something. Talcum powder mixed with the resin and catalyst is a very effective filler for small holes.</p>
<p>If the surface is vertical, and your patch large so its weight would allow it slip down, I use two sided tape to stick the DRY cloth onto the hole, then use a paint brush to paint the resin onto the cloth.</p><p>And talking about hulls, anyone have thoughts on applying gelcoat so it is a perfect smooth surface?</p>
<p>Hi there,as to applying gelcoat smoothly. Depending on the size of your repair,first give the area a light sanding then you can mix however much gelcoat you need,what I do is use the two inch celotape packing tape. I put the gelcoat over the spot then apply the tape,it smooths out the gelcoat and puts it in right where you want it.Let it cure 24 Hours just to be sure then take the tape off. There might be a little more sanding but not near as much as if you SMUUUDGED it all over! lol</p>
<p>If you want a properly strong and flexible finish, try this: since glass fibre mat is made up individual fibres thinner than human hair which are bonded together to create strands, the correct method is to stipple the mat with resin &amp; a brush until the strands are broken down into the fibres and each fibre is consequently surrounded by resin. The strength of GRP comes from the fibres not the resin, and so long as the fibres are surrounded by resin you will achieve the lay-up. Consolidating the area with a metal roller will make the whole thing far stronger and also bring excess resin to the surface. (Don't forget to clean equipment in acetone for next time!)</p>
<p>When wetting your patches, do it on a sheet of polyethylene (US spelling) sheet of some sort, such as the corrugated plastic campaign signs that are everywhere here. Don't do it in your hand. I would prepare a series of circular patches but I'd place the smallest first, and after painting the area to be patched with the resin. Smallest-first gives you flat, parallel layers.</p><p>Also, the warnings about curing may be overdone. Once catalyzed, resin is gonna cure. Slow or quick, but it'll cure. Letting sun hit it is also a catalyst. The fumes inhibit curing, and are heavier than air so if you are working in a bowl shaped place, you need a breeze to move those gases out.</p>
<p>Hi, when laminating a hole and where you have access to the outside of the repair, you should use a temporary backing to which the glassfibre will not bond. Eg a bit of polyprop plastic covered with polythene or cling film or a specialist non-stick material called peel ply. If doing this, you can lay some gel coat (to give a good finish to the outside of the repair), before adding the fibreglass layers. Hope that makes sense.</p>
Am a fiberglass moulder (lamination) I want a job in London
<p>Thanks for the great information!</p>
<p>I'll have to give this a shot at work. We' have some minor cracks and dents in the glass that could use some fixing up. If the problems keep up, we'll have to get a professional eventually. Otherwise, this doesn't sound like that bad of an idea to get fixed. I'll pass it to my superior and hopefully he'll approve this project.</p><p> http://www.ejfiberglass.com/Services/ </p>
<p>Thanks for the clear instructions, I repaired a large pot in a fountain after reading this.</p>
Edit: &quot;BONDO&quot;<br><br>(darned autocorrect)
Why didn't you use Bonding as the filler?
Good! <br>Went to my Blog, and see there, also, 2 Posts down, about Sandables: <br>http://faz-voce-mesmo.blogspot.pt/2013/01/reparar-fibra-de-vidro-rasperry-pi-e.html
Very useful info, Audrey, thanks for sharing it.

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