I spent about 30 years “hands on” in fiberglass
boat and mold
construction. Hull lengths up to 44 ft and with many varied materials and techniques.
Over those years I have come to the conclusion that 99% of blisters on a vessel are caused by poor work
practice or faulty equipment
used in the lamination process. Particularly during the gel-coat, skin coat and first structural layer of the layup
. This also applies to what people refer to as “delaminated” layers that in reality were not properly laminated to begin with.
A short list of what causes most blisters is as follows:
GELCOAT: Thin gel-coat, under catalyzed gel-coat or poor spray equipment
that allows oil
, water, or catalyst drops to contaminate the gel-coat film. Spray equipment that poorly mixes the catalyst. Also, in factory repairs
SKIN COAT: A skin coat that is too thin, an undersaturated skin coat, air bubbles in skin coat, waiting too long after gel-coat is sprayed to apply the skin coat, dust or trash or contamination between the gel-coat surface and the skin coat, under catalyzed resin in the skin coat, spray equipment that allows oil
, water or catalyst drops to contaminate the skin coat. Spray equipment that poorly mixes the catalyst.
FIRST STRUCTURAL LAYER: Undersaturated material, air bubbles in the laminate, waiting overnight to apply first structural layer, dust or trash or contamination between the first structural layer and the skin coat, under catalyzed resin, spray equipment that allows oil, water or catalyst drops to contaminate the laminate. Spray equipment that poorly mixes the catalyst. Exposure of the skin coat to sunlight or extreme heat prior to applying the first structural layer.
MATERIALS: Strand mat or chopped roving strand that has an excessive amount or highly insoluble binder. Really cheap
resin, really cheap
catalyst, really cheap chopped strand mat or chopped roving strand. Use of a DCPD resin (or any resin for that matter) that has poor secondary bonding characteristics.
After the first structural layer is applied and provided it is of sufficient thickness, the risk of poor work
practice and faulty equipment causing blisters is greatly reduced. It is not eliminated.
In my experience, the majority of blister and a lot of de-lam that is seen in hull and deck
structures are related to poorly trained and supervised applicators, poor work practices and improper or poorly maintained equipment. Faulty materials can normally be traced directly to the builder
ordering really cheap and substandard materials.