Splash Molded Disc

[Anthony Fairhurst]

Hello,

I recently made a couple molds for disc golf discs and have run into some issues that I would like some help on. Molds were made with a polyester gel coat down first and then after hitting the B stage, the reinforcement was added with Entropy Systems CLR resin/ CLF fast hardener and increasing weights of chopped strand fiberglass and finally woven carbon. I will use a slow hardener on the next one as the fast hardener kicked quickly and got very hot during the laminating process!

After both halves of the mold were done, the strong scent of polyester was still coming off so I figured it had not fully cured. I put the mold halves in the oven at 150F for 4 hours and when I pulled them out, I saw parts of the gel coat bubbled up and could flake off, exposing the resin below.

What is the cause of this and how do I avoid it in the future? Is it the polyester gelcoat and epoxy resin not liking eachother? Or is it because the epoxy resin kicked during the laminating process?

In the future should I try using epoxy just like gel coat? I had this gel coat laying around from an old project so figured I use it to make a good mold..

Thanks in advance!!

[John Kimball]

 

A couple things here to note. 

1. Your polyester gel coat is too thin. This will have a reaction when applying any resin to it. 

2. You can use epoxy with polyester gel coat, but you have to wait a bit longer. Too soon and the epoxy will react oddly.

3. Brushing gel coat can cause the streaks you see and can cause issues. If possible it’s best to spray it on.

 

Hope this helps.

[Anthony Fairhurst]

14 hours ago, John Kimball said:

 

A couple things here to note. 

1. Your polyester gel coat is too thin. This will have a reaction when applying any resin to it. 

2. You can use epoxy with polyester gel coat, but you have to wait a bit longer. Too soon and the epoxy will react oddly.

3. Brushing gel coat can cause the streaks you see and can cause issues. If possible it’s best to spray it on.

 

Hope this helps.

Thanks, John! I found a great article on this topic where it answered some of my question and you wrapped it up! In this article they explain this texture, which as you say, can occur from too thin of gel coat or multiple layers applied too quickly and results in "Alligatored" texture on the plug side (pictured below). I also did notice this texture was only occurring in thin spots so reasoning checks out!

This article covers a ton so let me know what you think of it!  https://explorecomposites.com/articles/tooling/building-open-molded-production-tooling/#gelcoat

What do you mean by "waiting a bit longer" before applying the epoxy? I thought waiting for the B-stage (gel coat is tacky but doesn't transfer when you touch it) was the proper application time. Should I wait an additional 10 minutes after the gel coat hits the B-stage?

I will make another mold this weekend with 2 coats of gel coat to ensure good coverage before applying the epoxy reinforcement. Also excited to use a slower hardener so I am not racing against the clock!

Edited September 7, 2023 by Anthony Fairhurst

[John Kimball]

Yup… alligatoring is the issue when you have thin spots. 
when using epoxy with polyester Gelcoat, I believe that if you start too soon, the styrene that’s still present reacts adversely to the epoxy and then has a hard time curing. Waiting until it’s not present anymore seems to be the solution. Also make sure that the Gelcoat is mixed properly.