If you own a fiberglass boat, you may eventually notice small cracks in the gelcoat finish that look like spider webs. These annoying little cracks are formally called crazing or spider cracks.
While not usually structural issues, they do allow water to seep in and damage the layers underneath over time.
Luckily, there are some relatively straightforward gelcoat spider crack repair methods to stop further damage.
What Causes Gelcoat Spider Cracks?
Unlike Stress cracks, Spider cracks often occur due to surface tension or minor impacts on the gelcoat layer.
Factors like prolonged sun exposure, changes in temperature, impact from docks or debris, and normal flexing of the fiberglass can cause the top gelcoat layer to develop small stress cracks.
Areas around hardware or seating are typical hotspots.
Gelcoat Spider Crack Repair Process
While tiny hairline spider cracks may not need immediate repair, it’s smart to fix them before they expand, allowing moisture ingress.
Here is a quick DIY gelcoat spider crack repair method:
Supplies Needed
- Acetone – cleans and degreases the repair area
- Scuff pad – roughens the surface for better adhesion
- Gelcoat repair kit – provides colored repair compound
- Spreaders/stir sticks – mixes the gelcoat filler
- Disposable brushes – apply gelcoat into cracks
- Tape – creates clean edges and removes excess filler
Steps To Follow
- Clean cracks: Use acetone and a rag to remove any dirt, grease or old wax from the area, ensuring a clean surface for the repair filler to bond to.
- Rough up surface: Lightly scuff a wider area around cracks using the included abrasive pad. This scoring helps the filler grab onto the surface better.
- Mix gelcoat paste per kit instructions – Correctly mixing the colored gelcoat filler according to the package directions is vital to get the right cure time and hardness.
- Fill cracks with paste, spreading evenly just past the edges – Work the gelcoat filler down into the cracks to displace any moisture, then spread evenly across the surface a little wider than the actual cracks.
- Pull tape along cracks to smooth and remove excess gelcoat – Before curing, lay strips of tape over each crack and peel back; this will level the filler and remove any extra material.
- Allow to fully cure – Leave the repair undisturbed overnight, or as directed by the kit instructions, to harden completely.
- Lightly sand if needed to smooth – Very fine sanding may be required to blend the edges evenly if any unevenness remains after full cure.
- Buff and wax repair – Final buffing and fresh wax around the repaired areas help restore luster and blend with the surrounding gelcoat.
Once cured, the gelcoat repair should be waterproof and blend with the surrounding area. Be sure to address what caused the cracks originally to prevent more from forming.
Preventing Spider Cracks While some crazing is inevitable over time, you can delay spider cracks by:
- Installing boat fenders and avoiding impact
- Keeping the boat covered when not in use
- Waxing regularly
- Avoiding using harsh cleaners
Spider Crack Repair FAQs
Here are answers to some frequently asked questions about dealing with gelcoat spider cracks:
Very fine hairline cracks may not need filler yet. But if wide/dark enough to allow water ingress, or cause the surrounding area to be porous, repair is recommended.
Using a colored gelcoat filler matched closely to your boat’s existing gelcoat works better than basic epoxy, allowing for an invisible repair that will last.
While not typically a structural issue, cracks that penetrate deep enough to allow underlying wood or laminate layers to get wet will lead to more expensive repairs if ignored too long.
No – While acetone effectively removes dirt and wax before repairs, it can dull uncured gelcoat and is not generally advised for overall cleaning. A boat-specific soap and water works better for normal washing.
I hope these expanded FAQ’s give you more insight into effectively dealing with tricky gelcoat spider cracks! Let me know in the comment section below if you have any other questions.
Final Word
Catching small spider cracks early and repairing them properly ensures your boat’s gelcoat stays protected for longer.
But if cracks reappear or spread, it may also be wise to consider repainting the most affected sections to get a fresh start.
You should also read my article about repairing all types of gel coat cracks on a fiberglass boat here.
