Common Problems in Fiberglass Pools

Why do Fiberglass Pools Blister?

Osmosis quite simply is the physical process by which a liquid from a weaker medium is drawn through a semi-permeable membrane into a stronger liquid medium.  This is a process called Hydrolysis, a general term given to the reaction of any material with water soluble corrosive products which in turn create the cavities or blisters.  For example, organic compounds like polyester resin are the main constituent to GRP (Glass Reinforced Polyester) laminates, which created a phthalic acid.  The water molecules are so tiny that they actually pass through the gel coat surface of the pool.  When they are allowed to come in contact with cheaper polyester resins they create blisters and expand with heat or direct sunlight.


The two fundamental causes of GRP blisters are:

  1. Poor workmanship in manufacturing
  2. Water getting into the laminate.

Cobalting or Black Dots are miniscule air holes that develop when the gel coat is applied.  A second coat of the gel coat will negate the possibility of cobalt spots.  There are a couple of methods of reducing the Black Cobalt Spots:

3. Cobalt Treat can be purchased at a local pool store, manufacturer: United Chemical/Bioguard

4. Citrus Acid (a weak organic acid) used to remove stains and cobalting

Which means that the manufacturer was using an inexpensive product, when in fact they should be using an epoxy resin such as AquaGuard®, a thick film that is 100% solids reinforced epoxy based polymer designed as a protective coating with great chemical resistance.  This process is now being used in the Fiberglass Pool Industry.

The repairing of blisters in fiberglass pools and/or spas can be easily repaired with AquaGuard PATCH KIT.