Document Type

Conference Proceeding

Date of Original Version



Tests were made on gel coated orthophthalic-fiber glass test panels to evaluate the effectiveness of coating materials as barrier layers to prevent or impede the development of blistering. An epoxy, a polyurethane and a polyester were used alone and in combination as coatings. Different surface treatments of the gel coat before coatings were added, were also evaluated. Following an immersion test in distilled water at 65 degree C, the panels were examined for blister initiation and blister severity. The results are interpreted based on a diffusion model through a two component layered structure in which each layer has different permeability and saturation values. Leaching rates which may be very important in blistering were taken into account. The major conclusions are the following: surface treatment improved the adherence of the coating to the gel coat and sand was generally the most effective treatment. Two types of blisters were observed - coating blisteres which formed between the top coat and gel coat were small (1 mm and less), flat and circular. Larger blisters, more irregular in shape, formed below the gel coating. All samples blistered after six weeks at 65 degree C with the exception of the polyester on polyester and the polyester with no undercoat samples. These were not blistered after 11 months. Diffusion analysis suggests that the polyester coating on the gel coat modified the transport properties of the gel coat.

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