To:  Multi-Tech Products

I am a new surface repair tech, and I am having difficulty getting a good cured repair on gel coat bathtub repairs. The surface remains tacky too long, and doesn’t achieve a satisfactory hardness. What am I doing wrong?

The most common problem repair technicians have is “a tacky surface” after the sprayed gel coat has completed its heat cycle. The easy explanation is they have attempted to use a short cut in the application.
Many repair pros try to spray gel coat through a Preval® sprayer, since it is easy and convenient. This sprayer is an aerosol set up that allows mixing the ingredients in a glass jar. It is then atomized at low pressure using an aerosol source.
The low pressure requires the gel goat to be thinned excessively for spraying. This results in creating a recipe outside of the manufacturer’s requirements for optimum performance. Technicians have reported to us they try to use acetone as a thinner and create a 50% mixture. Every gel coat chemist says “do not thin gel goat more than 10-15% and use styrene only”

Gel coat is made for production factories “ready to spray” at 60-80 psi at the gun. Catalyzing at the gun tip yields optimum chemistry in this setting. The mold keeps oxygen away from the surface and gives the maximum hardness to the sprayed gel coat surface. When cured gel coat is pulled from the mold’s surface, there is absolutely no tackiness.

To duplicate this result in a repair application and achieve a tack free finish, you must:
-Spray pure gel coat at the recommended pressure (50-60psi). This requires an air compressor and proper spray gun or air brush.
-Spray it as close to the original manufacturer’s formula as possible (thin no more the 10-15%)
-Catalyze to between 1 to 3% with 90% MEKP
-Thin only with styrene.
-Most importantly, seal the surface at “peak exothermic cycle” with PVA.

All materials and tools are available from us. Using the proper materials and equipment will yield a more professional result, and a happier customer.

For more information on proper application of gel coat go to:

Ken Wolfe
Consulting Chemical Engineer
Multi-Tech Products Corp.