Ever wondered what causes those annoying fine cracks in gelcoat? And more importantly how do you make them go away? Read on to find out about an easy solution to this age old problem.

What causes gelcoat cracks?

Hairline cracks, stress cracks or spider cracks (star cracks) that occur in gelcoat surfaces on fiberglass boats or other water craft are often seen as a cosmetic issue.

In most cases this is true, however it is important to seal them correctly otherwise water may penetrate into the fiberglass and cause more serious damage.

Most stress cracks occur in the gelcoat layer of fiberglass surfaces and can be repaired by yourself. If structural damage is suspected, you should get your boat inspected by a qualified boat repairer.

These problems occur as a result of:

  • Manufacturing defects
  • Environmental challenges
  • Stress and movement

Also, older fiberglass boats tend to have a thicker application of gelcoat which means they are more susceptible to cracking. Stress cracks first appear as very fine hairline cracks. Over time, the cracks get larger and the structure may begin to delaminate and/or blistering starts to occur.

The main causes are:

  1. Swelling of the resin due to water diffusion
  2. Wave action and rigging stresses
  3. Direct sunlight or thermal shock on darker colored gelcoat can cause warping, delamination and blistering
  4. Impact
  5. Expansion or contraction

How do you tell what the cause is? By the pattern of the crack:

  • Radial cracks  (spider cracks, star cracks) – caused by impact or by a fixture / bolt that puts strain on a certain area of a boat and cracks occur around the hole.
  • Linear crack – caused by flexural strain
  • Thermal fatigue cracks –  when gelcoat repeatedly expands or contracts. These might be in a parallel pattern or a non-directional pattern

How to avoid gelcoat stress cracks?

Spider cracks can be avoided by countersinking holes just through the gelcoat, so the load is placed on the structural fiberglass rather than the brittle gelcoat. There’s also a great article on how to drill holes correctly to avoid chipping and cracking in fiberglass.

Quite often however, it’s near impossible to prevent these unsightly cracks due to the fact gelcoat is so brittle and rigid.

How to repair gelcoat cracks

One quick and easy way to repair gelcoat stress cracks yourself is by using MagicEzy Hairline Fix – A purpose built DIY repair solution for stress cracks in gelcoat and fiberglass.

MagicEzy Hairline Fix is a one-part, pre-tinted (available in 10 colors) sealant that allows you to complete the repair in seconds without having to grind out the existing damage. It requires absolutely no tools and once complete the repair is guaranteed to last by MagicEzy.

Watch the video below to see just how easy it is.

MagicEzy Hairline Fix

Below are real before and after images of a MagicEzy Hairline Fix repair taken from the Bayliner Owners Forum.

MagicEzy-Hairline Fix-Before-After-BOC
Image source: www.baylinerownersclub.org/index.php/forum/general-boating-topics/55481-crazing-repair-before-and-after

Here is another one courtesy of the BoaterEducation Forum

Hairline-Crack-BF-AF
Image source: http://www.boatered.com/forum/topic.asp?TOPIC_ID=164951