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Fixing Fiberglass Cracks - Keeping Fiberglass Solid

Crack is whack, especially when it’s in your RV’s fiberglass! Since the majority of the exterior is usually made up of fiberglass, knowing how to fix those cracks can come in handy! If you have a fiberglass roof it’s especially important to get damage fixed as it happens so you don’t end up with moisture under it and inside the ceiling of the RV. When looking at cracks you may find that there are generally two different types: gel coat or surface cracks, and structure cracks. The gel coat cracks are simply cracks in the cosmetic layer that’s put over the top to keep the RV looking shiny. These are the easiest cracks to fix as they’re not very deep. If you have a structural crack that means the entire piece of fiberglass has cracked through. The repairs for the two will be relatively similar, but with a few extra steps if it’s cracked all the way through.

What you Need

If you don’t already have it, make sure you get proper protective gear for your skin, eyes, and lungs. Keep in mind that fiberglass is just that! Made of tiny fibers of glass. You don’t want them stuck in your eyes and hands, and you definitely don’t want to breathe it in! Protect your eyes with safety glasses, wear gloves, and a mask or respirator. If you do not have these items, be sure to add it to your shopping list, no matter what kind of cracks you’re looking at. There are a lot of kits and quick fixes out there that you can get, but we recommend taking this on at a deeper level so you can ensure it’s not going to come back. You want to have a good strong bond and with inexpensive kits, the materials are generally sub par. That is not to say that all kits are bad. West Systems makes kits that come with everything you need to make the repair. Not only do they have kits, they have step-by-step written instructions, as well as videos you can follow. While you will find that these are all about boats, the fiberglass is the same which makes the repair process the same. All of the following items, with the exception of the sand paper and acetone, come in their Fiberglass Boat Repair Kit:
Shopping List

  • 80 Grit Sand Paper for your sander

  • Resin

  • Hardener

  • Fiberglass Fabric

  • Adhesive Filler

  • Fairing Filler

  • Glue Brushes

  • Mixing Pots (something disposable)

  • Mixing stick

  • Application Syringe

The Repair Process

As you can imagine, there are going to be additional steps you need to take to repair a deep structural crack as opposed to a gel coat crack. Ensure you follow all the instructions, including the area prep for the kind you’re working on. Failure to properly prep the area before hand will result in the repair coming back off and you will be out the money, time, and still have the crack.

  1. Sand around and down into the crack. You want to clean away enough to expose under the gel coat and get down to the actual glass so that you can get a good bond. With gel coat cracks, you will basically be sanding away the entire layer that is cracked.

  2. Clean the area well with acetone. This step is crucial because any dust or dirt will prevent the patch from bonding to the surface and it will simply come right back off.

  3. Mix the resin and the hardener according to package directions

  4. Fill the crack with the epoxy mixture you just made. Do this a little at a time, especially if you are working on a large area. This mixture creates heat as it sets up and hardens, and if the layer is too thick it can actually start on fire due to not being able to let off enough heat!

  5. Once the filled crack is hardened and set, sand it smooth

  6. Clean the area again with acetone. (for gel coat cracks skip to step 15 next)

  7. Rip off a piece of the fiberglass fabric that is just larger than the crack so that it can overlap. Don’t cut it! This creates blunt edges and will mean that you will have to do more sanding to get everything to blend later.

  8. Wet the surface of the RV with your epoxy mixture

  9. Lay your piece of fiberglass fabric over the crack.

  10. Blot the epoxy into the glass with a cheap paintbrush. Wiping will pull strands of glass out. If there are bubbles, tap them toward the edge of the fabric to get them out.

  11. Let it get tacky

  12. Add another layer if needed, and make sure that this one is just larger than the last.

  13. Once the patch has cured, sand it down so that it is smooth

  14. Clean with acetone again

  15. Trowel over the top with the fairing filler mixed with the epoxy mixture. You’re looking for a peanut-butter-type consistency.

  16. Swipe back and forth in different directions to ensure you fill all pin holes.

  17. Once this layer is dried you can sand, prime, and paint!

Fixing fiberglass can be relatively easy for some and a tough task for others. If you’re not up to the challenge, don’t fret! Call pretty much any marine store in the area and you will be likely to find that they are willing to fix those cracks for you! Having it professionally done ensures a good finish that’s structurally sound.

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