GEL COAT -- What am i doing wrong? now i know!

[zorg]

fettster did tell me about the baby powder trick ,although i had heard of it before i thought it only applied to runny resin rather than this gel stuff.

as for spraying, i have not tried it, how do you go about it?

i would have thought it would be too thick to go through a spraygun?

-z

 

[foxbatkllr]

Spraying is nice, but the spray guns are expensive and they don't work for every project. Some molds are difficult to spray into because of their shape. Honestly, I've had good success brushing gelcoat. Gelcoat can have a problem sticking to silicone sometimes when you brush it on, but to say you should never brush it into a silicone mold is ridiculous. It's manageable and its much better than having no gelcoat IMO.

 

[zorg]

well i have been wiping down the surface of the mold with acetone and the gelcoat seems to brush on fine, almost no air bubbles now.

i think for the amount of times i'll need to spray gel coat its not work the outlay.

a lot of the things i do would not be suitable for spraying anyway.

-z

 

[exoray]

Spraying is nice, but the spray guns are expensive

You can get by with a $15 Harbor Freight spray gun with the tip drilled out to give or take 2mm... I hear that you can actually contact Harbor Freight customer service and they will order you up the larger tips, IMO it's easier to just drill them out, you are not really overly concerned with a nice spray pattern, so the hack job with the drill will work...

20 Oz. High Volume Low Pressure Gravity Feed Spray Gun

Hardly a perfect gun but it will get the job done, some people even use cheap engine cleaning chemical sprayers...

Amazon.com: AIR ENGINE CLEANING GUN WITH WAND & HOSE: Automotive

These certainly are not the ideal tools for the job, but they will get the job done for the casual hobbiest that doesn't want to brush, and also wants to keep the outlay minimal...

Cleanup on these guns is not always the easiest but a 5 gallon bucket with a gallon or two of acetone in it and a suspended screen bottom will help with cleanup...

I personally gave up on polyester gel coats, in favor of a proprietary urethane blend that I worked up after much trial and error... As said above though the polyester layup doesn't readily bond to urethane in general, so you need to work out that issue... The above cotton flocking is one way there are others... I just find the urethane to be more predictable for my needs...

Also what you really should do when you are new to fiber-glassing is keep logs, get a humidity and temperature gauge and keep detailed logs of humidity, temperature, catalyst ratio, work time and cure time and your overall opinion of the end results good and bad... As your log and experience grows you will discover the sweet spots that work... You will also discover real fast just how much havoc humidity and temperature can play with polyester, and how important it is to adjust the catalyst for varying conditions... In time you will just get the knack for it, but the logs are always good reference...

 

[womo68]

Great thread. I have a question....I have molds (silicone) and every time I use gel-coat it seems to crack a little as if it shrinks. I have to go back and fix the areas with bondo. I'm assuming when it kicks it shrinks. I also slush it around until it kicks....so no brushing it on.

So question is....Is there a way to keep the gelcoat from pulling away from the molds?

 

[zorg]

wayne, i found by reducing the activator solved that problem, no pulling away from the mold and no cracks (i got them too)

-z