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How to Repair a Fibreglass Crack for Beginners

Repairing a Fibreglass Crack doesn’t have to be daunting. We’ve put together an easy to follow guide specifically aimed at those new to fibreglass!

As always if you missed any of the steps outlined in the video, please keep reading. If you have any questions or would like to buy any of the products featured in the video, you can find them (and us!) at https://www.fibreglassdirect.co.uk.

Step 1: Familiarise yourself with any MSDS or TDS sheets prior to purchasing or using the fibreglass materials. These products are hazardous and have a strong odour so great care should be taken on how and where you use them.

Step 2: Inspect the area to be repaired. In this case we are using an old fibreglass lid. Sand the inside of the product using 80 grade sandpaper.

Step 3: Take a clean cloth and wipe down the sanded area with Acetone.

Step 4: Weigh out 0.5kg of resin. Add catalyst at a rate of 2% e.g. 20ml for every 1kg and mix well. 2% applies for room temperatures.

Step 5: Brush on the resin and apply the pre-cut mat to suit your area to be repaired. Apply more resin and roll in with a paddle roller. Repeat this process until three layers have been applied.

Step 6: Leave to cure at room temperature for 3-4 hours.

Step 7: When the resin has fully cured, sand the area with 80 grade sandpaper and clean the dust with Acetone.

Step 8: Sand the cracked area on the outside of the product using 80 grade sandpaper.

Step 9: Using a cloth and Acetone, clean the dust from the sanded area.

Step 10: Mix 0.1kg (100g) of Gelcoat, adding catalyst at a rate of 2% – again using room temperatures. Mix thoroughly.

Step 11: Using a mixing stick, apply Gelcoat to the cracked area.

Step 12: Carefully apply masking tape, lifting back to ensure that no air pockets have been trapped in the Gelcoat.

Step 13: Leave to dry for 3-4 hours at room temperature.

Step 14: Remove masking tape and clean down with Acetone.

Step 15: Sand the cured Gelcoat starting with 180 grade sandpaper and finish with 1000 grade. Wet the sandpaper with water first.

Step 16: Apply Farecla compound to shine and finish the repair!


  1. easy on a Lid, and by a Pro….LOL

  2. what chemical can be use to fix a broken mannequin??

  3. So one has to weight the liquid then add 2%…….I don't think that explanation makes it any easier if someone understands the metric system or not. You are dealing with liquids, can't there be something like mix this much ml of resin to this much of ml of catalyst? Sorry, this is confusing that way it is presented and has nothing to do with metric or standard. I can say for certain that some of you bashing the standard system don't even know to figure out what 2% of 0.5 kg is.

  4. Great video and very helpful!, thanks!

  5. That was brilliant. Straight forward without all the bullshit dialogue.

  6. This is exactly how I fixed my bathtub and pool slide 😂

  7. Good video… rubbish music

  8. Music is annoying..! Had to mute it.

  9. How do I repair it if I can’t get to the backside of the crack

  10. Very good video – however it's difficult to work with units like kg and percentages for resin and catalyst, is there a reference using the units on the product labels – ie: ounces? Ratios are tough too…hard to be accurate. And how do these ratios change with temperature? Would you recommend doing this in 40-degree weather? Second question is, if the crack is deeper, and your first application of gelcoat still leaves a depression, can you simply repeat the same process to add more material? How is the gelcoat surface prepared for a second "coat"? Lastly, will any type of masking tape work or is this a specific type for this application?

  11. Does this work for bath tubs crack?

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