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Repairing Gelcoat Crazing in a Polyester Boat

Small hairline cracks and spider-webbing in the polyester surface can be frustrating, as they spoil the appearance of your boat hull or interior. Spider cracks are generally difficult to repair. Often, applying a filler is challenging because the damage is very shallow and requires extensive sanding or grinding. In this article, we guide you step by step on how to repair hairline cracks in gelcoat. Follow all the steps carefully, and your hull or deck will look as good as new!

Do you have questions about a gelcoat repair or boat maintenance? Please feel free to contact our product specialists. We are happy to help you make your project successful!

What are gelcoat spider cracks?

Spider cracks are small cracks in the gelcoat. These hairline cracks often occur naturally due to the aging of the paint system. By repairing gelcoat spider cracks with IJmopox ZF Primer, the treated surface looks great again.

Repair gelcoat spider cracks [manual]

Supplies

Step 1. Cleaning

Before repairing hairline cracks in the gelcoat, it is important to clean the gelcoat. For this, use a high-pressure cleaner or Riwax RS Boat Clean. By cleaning the surface properly, you will clean the cracks well and spray away loose pieces of gelcoat easily.

Step 2. Sanding

Sand the entire surface with 180-grit sandpaper. By sanding the surface, you improve the adhesion between the gelcoat and the ZF Primer that you will apply. After sanding, degrease the surface with Double Coat degreaser.

Step 3. Repairing loose pieces of gelcoat

During sanding, spots may have appeared where the gelcoat has come loose. Touch up these areas with Variopox Epoxy Filler and then sand again. 

Step 4. Applying IJmopox ZF Primer 

We are going to repair the gelcoat crackle with IJmopox ZF Primer. Before using ZF Primer, read the technical data sheet carefully. It contains important information about mixing ratio, amount of thinner, consumption and application.

Instructions for use of ZF Primer

  • Determine the desired quantity and weigh both components on a digital scale according to the mixing ratio 87:13.
  • Mix the base and hardener well.
  • Apply ZF Primer with a velour roller.
  • Immediately smooth the surface without pressing hard and rub the layer into the crack with a filler applicator.

We recommend applying 2 coats of this epoxy primer. 1 layer without thinner and then 1 layer with thinner. When working with ZF Primer, always wear covering clothing and nitrile gloves.

Step 5. Follow-up

When you have applied ZF Primer, the tiny cracks that cause gelcoat spider cracks will have been filled. We recommend sanding the surface again with very fine 200 grit sandpaper (dry). After this, you can continue with step 4 of the painting instructions for your deck or hull.

More information about repairing hairline cracks in gelcoat?

Do you have any questions about a gelcoat repair or about repairing crackle? Feel free to contact one of our specialists. We will be happy to advise you to make your project a success. Send us a WhatsApp message or email to support@polyestershoppen.com for free, no-obligation advice.

Frequently asked questions

What is gelcoat crazing and how does it occur?

Crazing refers to fine hairline cracks in the gelcoat, typically caused by ageing, UV exposure, and stress in the material. It is common on older boats or surfaces exposed to sunlight for extended periods.

How do you repair crazing in gelcoat?

Start by cleaning and sanding the surface, then apply IJmopox ZF Primer. Use epoxy filler for any loose areas. The primer effectively fills the fine cracks.

Can I repair gelcoat crazing myself as a DIYer?

Yes, with the right products and our step-by-step guide, you can repair crazing yourself. Contact our specialists for advice if you’re unsure.

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Products used in this article

Product 1 of the 5
Often chosen Topcoat in colour (5kg)

Pre-coloured topcoat (ISO-NPG)

€ 25,99

In stock

  • Available in all RAL colours
  • Cures tack-free
  • ISO-NPG quality
Often chosen Variopox epoxy filler

Variopox epoxy filler

€ 36,99

In stock

  • High chemical resistance
  • Waterproof after curing
  • Adheres to polyester and epoxy
Recommended Double Coat Degreaser

Double Coat Degreaser

€ 13,00

In stock

  • Very strong degreaser
  • Also removes silicone
  • For a professional result
Recommended IJmopox ZF Primer

IJmopox ZF Primer

€ 39,99

In stock

  • 2-component epoxy primer
  • Good rust-preventive properties
  • Excellent adhesion to metal
IJmopox Thinner (HB Coating and ZF Primer)

IJmopox Thinner (HB Coating and ZF Primer)

€ 13,99

In stock

  • For ZF Primer and HB Coating
  • For processing with air sprayer
  • Thins strongly

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Do you have a specific question? Call one of our specialists for free advice +3185 0220090