COMPOSIT 101,202 AND ADVANCE Newsletter.

-Gelcoat bubbles.

In this issue of the Composite 101, 202 and Advance Newsletter:

1. A composite question from a subscribers

                                                                                   
1. A composite question FROM SUBSCRIBERS.

This newsletter question is a classic sent by J. Dannhauser:

I keep getting that: my gel coat makes bubbles as soon as I take it out of the mold, only on certain areas on the boat. When I grinder the bubble open it makes like fluff as if the has been no resin. What am I doing wrong?

Composite 101, 202 and Advance answer:
There are two causes of bubbles on the gel coat. One is cause by air entrapment while the other is caused by contamination.

• In Image 1 – Air entrapment.

At looking at a part often you won’t be able to see the entrapped air (often called air bubble). If big enough the  bubble will show right after the demolding of that part, you will se a slight deformation in  the gel coat if you push again it you will burst the bubble by cracking the gel coat. You may also see un-wetted material just like in the left portion on the image 1.
         
If you are using hand layup to laminate your part than the probable cause is you need to use more laminating roller to get the air out. There’s a wide range of laminating roller to accommodate the shape of your mold. As explain in Composite 101, 202 and Advance visual guide. When rolling a light fabric the air bubble will rise to the surface and burst, but with a heavy fabric you got to use a laminating roller to drag the air out from the mold in other word roll from the center toward the exterior the mold to bring the air out.

To find out if your parts have air bubbles, expose it to heat. Use a stripping heat gun to heat the surface (just send heat wave on the gel coat you don’t want to cook the it) you want to use slightly more heat than a hair dryer will produce. When heating the air bubble the gel coat will deform revealing the air bubble.

• In Image 2 – Contamination.

Contamination will prevent the resin from curing properly. The Two most common source of contamination is from catalyst and sweat.

Contamination from catalyst, happen when the resin is not properly mixed and there’s a twirl of catalyst in the resin bucket. This poorly mix resin, when applied, will prevent the resin from properly harden and stick to the gel coat causing the bubble like in the
Image 2.  

Also common in hand layup is contamination by sweat. When leaning over the mold to laminate, sweat from your forehead can drip in the mold cavity on to the gel coat. Some resins are more influence than other to humidity and can cause problems.

You have also to keep an eye open for grease, oil and silicon that could come in contact with the gel coat and prevent the resin to stick to the gel coat.

Sincerely,
__________________
Mr.Carol Fortier
Project manager
www.fiberglasstechnique.com