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Gelcoat Repair : How to repair cracks and chips in damaged gelcoat

This video is a step by step on how to properly repair your cracked gelcoat. Justin at The Skiff Shop shows us his process of grinding out the old gel coat, filling these cracks with resin paste, applying the new gelcoat and buffing it out! Hope this video is helpful with your project. Please subscribe to our channel for upcoming how to videos!

MEKP : https://fiberglassflorida.com/catalyst-mekp.html
AEROSIL : https://fiberglassflorida.com/aerosil-cabosil.html
ADTECH : https://fiberglassflorida.com/adtech-77-filler.html
CARBON GUIDE : https://fiberglassflorida.com/fiberglass-supplies/fiberglass-supplies-buffing-polishing/3m-dry-guide-coat-cartridge-and-kit.html
GEL COAT : https://fiberglassflorida.com/gel-coat-isophthalic.html


  1. Beautiful work! I repair a lot of fiberglass and epoxy surfboards! It is def an art. Well done 😎🤙

  2. I'd love to see before and after both surface and zoomed in.

  3. Ive got a few chips and spider cracks I need to repair all up on the top of the boat and one what looks like an impact spider crack on the deck. The problem is my deck is factory non slip with little diamond patterns cut into the fiberglass. How the heck can I sand it after repairs without messing up the floor? As a matter of fact just opening up the cracks is going to take out some of the pattern in the little nubs.

  4. Just when I thought I could buy a cheap gelcoat repair kit lol

  5. Great video, thanks for posting. Justin, your attention to detail is first rate and a credit to your workmanship. The finish looked perfect.

  6. Kudos young man. mad skilz.. much respect from an OG

  7. did a very good job enjoying the non-fiberglass people how to do it one more tip I would add to you is that the end of every crack drill a very fine hole that way you'll stop the fiberglass from continuing its crack

  8. So, a few tip to add from someone who does this a frighteningly large amount of the time.

    If you've got a large crack or scratch that penetrates to the chop layer, then you should not rebuild the entire thing with the Gel Coat. As stated, the shrink is actually much higher on it, and leftover internal stresses from a large blob will cause issues. Use Bondo and some chopped fiberglass to rebuild the structure. The bondo is filler, while the fiberglass fragments are where your strength comes from. Aim for about a 10-12% per weight ratio of Bondo to fiberglass. Once hardened sand and make sure the surface is rough but not jagged (100-200 grit sandpaper).

    Whenever you mix gel you should pay attention to a lot of things. You're looking for 80 degrees ambient minimum (usually 90 is target), with about 20-40% humidity. This is hugely important for not retarding the cure time. 10 degrees isn't a lot, but it can double cure times. You're aiming for about 1.5% catalyst (MEKP) to 98.5% gel by weight. You can eyeball it, but it's a potential failure mode. This mix will give you a pliable but thick coverage for deep damages.

    If you're using a wren gun, or other air tool, aim for 1.5% catalyst, 70% gel, 28.5% acetone mix. The acetone will retard the cure time, but it will allow the material to flow through most gun tips without too much issue. Flush the tip with pure acetone afterwards, or the gel can gum up in the tip.

    Once you apply the gel with either the air gun or as a paste allow to cure until tacky. The next bit is a huge time saver, so take it for what you will. Once the outside edge of the patch dries fully, but the inside is barely cured, gently wipe the surrounding area with an acetone laced paper or fiber towel. You'll thank me because a lot of your overspray and debris from around the patch will quickly be cleaned off with only a gentle rub. Allow the rest of the patch to cure fully, then begin the evening process with your sandpaper.

    For sandpaper, you've got a lot of choice. I'd recommend 3 different grits. 400, 600, and 1000 work best in my experience. 400 will allow you a shape, but not aggressively. 600 removes the remaining bits, but is fast enough to not take all day. Finally, 1000 gets you to a place where the buffing compound will absolutely shine it up, and again will allow for this to happen quickly.

    Finally, buffing. Your two friends here are either a red rouge stone, or polarshine. I know the later is a product, but the other stuff I've used is aquaglass…and I wouldn't recommend. Apply the rouge stone to the buffer, or the abrasive to the surface. Buff in tight circles, oscillating the head so that no one spot on the buffer head makes contact for more than 10-20 seconds. I see that using the edge is done in the video…but when you're looking for more control you should use the buffer face. An edge can easily grab onto features and wind up causing issues. Not to say it's not valid, just a lot more prone to failure. I personally would recommend red rouge for most people. The stick is stable, it'll last months or years for the average person, and it doesn't dry out into a flaky lump if left unattended.

    Now…why should you listen to anybody in the comments? Well, the simple answer is that I make Bathtubs. I've been white head to toe more than once, and I've repaired everything from a surface crack to a gigantic missing chunk because somebody decided to jump around in a bathtub and put their foot through a seat. You're welcome to discount the advice…but it's hard to consider it trivial when you've got 300+ units to finish in a day and about 5 minutes a unit of repair within cycle time. I could be lying…I could be pulling ratios out of thin air. Believe me if you're willing, but I can attest that boating and bathtubs are functionally the same process…and those with experience might know the MVP of guns in more Venusian than you'd think….

  9. Hi, what brand of pneumatic polisher you use? Best regards

  10. I got this job to do on my boat, I thought to dremel the cracks, then use gelcoat putty only, here I am seeing he is first closing it up with polyester resin and cabosil, then after he is using gelcoat. is the gelcoat alone not good enough?

  11. Where do you get that carbon stuff? It's new to me

  12. Best video clear and very clear explanation with patience step by step 👌 thank you for sharing

  13. No cutting corners here. Fine job!

  14. Nice job on the light repair.

  15. Mylar film over smaller repairs can eliminate or reduce need to sand , smooth and polish.

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