Minor Gel-Coat Repair – Part I

Fibertex & Supply
Minor Gel-Coat Repair – Part I

At FiberTex & Supply we specialize in repairing boats to match their original condition. If you don't want to shell out the cash and think you can tackle it on your own, here's a few tips on doing the work yourself. A steady hand and an eye for detail go a long way.


Latex gloves, stir sticks, paper cups, artist brush, acetone, gel-coat, MEKP catalyst, cabosil, putty knife.

Gel-coat is a basically a pigmented resin and when catalyzed with MEKP (Methyl Ethyl Ketone Peroxide) it cures hard. Most gel-coat you buy at the marine supply store is finishing grade, which means it has a surfacing agent already mixed in. Gel-coat without surfacing agent will never cure hard in this application. Acetone is the most commonly used chemical for cleaning resins and gel-cote. Do not use plastic party cups or styrene cups to mix chemicals, the cup will melt.

Cabosil is a light powdery substance used to thicken resin. Use a mask when handling cabosil; due it its lightweight nature cabosil can easily become airborne and inhaled. Small amounts may be purchased from a fiberglass repair shop or a marine supply store.

We can not stress safety enough! These chemicals are dangerous! Wear a mask, wear gloves, and be careful!

Minor gel-coat repairs are defined as non-structural repairs not needing fiberglass. Types of gel-coat damages can be voids, chips, and scratches.

Shallow surface scratches can usually be wet sanded with 400,600, and 1000 grit wet-sand paper. Use a spray bottle and sand with long smooth strokes. Focusing on the scratch only will develop a groove in the gel coat. Follow up with 2000 grit buffing compound to polish it out.

Deeper scratches and chips that expose fiberglass are best repaired by those with the capability to do body work and spray gel-coat. The repair we explain here is more of a 'touch up" repair used to cover up damage. Exposed fiberglass from a chip or scratch is only cosmetic damage. However, exposed fiberglass subject to UV rays (sunlight) is a recipe for de-lamination and future structural damage.

If you can get the original gel-coat color of your boat this would work best. Color matching gel-coat takes years of practice to master, but even then some colors are nearly impossible to match perfectly. Gel coat pigments are available at most marine supply stores if you want to try your hand at color matching.

First, with a dremel tool or folded sand paper, lightly "scuff" the groove of the scratch or chip. Scuffing the area will help ensure a strong bond. Clean the area to be repaired with a rag dampened with acetone, removing any dust created from scuffing the area. Acetone is best because it evaporates quickly.

Use masking tape create a "box" around the area you plan to fill. Use two layers to form the box. Additional layers around the outer edges ensure easier removal after new gel-coat is in place.

Pour gel-coat into small paper cup, add cabosil, and stir until the gel-coat creates a peanut buttery paste. Lumps of cabosil in the gel-coat means you have not stirred enough. If the gel coat will pour out of cup you have not added enough cabosil. Stir until you have a smooth uniform texture.

With a mixing stick, scoop gel-coat putty onto a mixing board. Add a few drops of catalyst and mix thoroughly. Use a putty knife to fill in the damaged area. Make a few passes over the area to work out any air bubbles and to ensure and smooth level spread. The gel-coat putty should not be built-up too high, it should be flush with the masking tape. But definitely do not under-fill the area because there is a chance of shrinkage as the gel coat cures. If you build it up too high at least you can sand it down. Remember! you don't have a lot of working time so work quickly.

Join us back here next month and we'll show you how to sand and polish the gel-coat to obtain a classy-looking repair job.