Pre release gelcoat

Hi all,

Earlier today, I sprayed gelcoat on a new sea kayak plug I’ve just finished. I've made around 10 molds before without any issues, following the same procedure.

After applying the gelcoat, I turned off the air conditioning, and the temperature rose to about 30–32°C (86+°F). I left the plug for 3 hours, and when I returned, the gelcoat was fully cured as expected—but a large section had already pre-released from the plug.

To manage the situation, I immediately applied a layer of 150g/m² mat just so I could safely remove the gelcoat without it shattering. I assume I’ll need to remove everything and start over?

The pre-release is worst near the bow, even into the main deck area. Most of the flanges are unaffected, except near the bow. Visually, the shape looks okay, but when I press some areas with my finger, I can feel the gelcoat has detached from the plug.

The only factor I can pinpoint is the high temperature. I used the same process I always do—Easy Composites sealer as per instructions, followed by six coats of wax. I’ve used this exact technique many times without problems. The only difference this time was the elevated temperature, and I suspect that gelcoat shrinkage during curing caused the release. I used 2% MEKP catalyst.

I haven’t made any molds during the summer before due to heat concerns. Based on your experience, does my assumption about the temperature and shrinkage sound accurate?

Thanks in advance for any insights.

 

With a fairly rapid increase in temperature there may be some outgassing or conversion of some of the more volatile substances present.You will not enjoy the process of removing the material but it is less work than attempting to press on to a full laminate and then trying to repair the poor piece you would have.

 

You can drop to 1.5% is it's hot out.

Keep a fan blowing on it while it cures, this will help the cure to be uniform on the entire part.

Uneven gel coat, or it being too thick can result in pre-release, especially in tight sections.

A blended catalyst will help a great deal, MCP75 or similar.

Laminate sooner.

Or just don't do it when it's hot out unless you keep the air conditioning on.

 

Was the area of delamination the first area sprayed?
Perhaps contamination from solvent or old material in the hose?
Contamination of the mold surface?
I’ve sprayed a lot of gelcoat in molds in less than ideal conditions, and have seldom had problems, thus my leaning towards contamination as prime suspect.
Perhaps keep the AC on to dehumidify through cure time, just turn the thermostat up a bit to help the gelcoat kick.

 

Not really.

I pay very much attention when spraying (the prep cleaning etc), sprayed already many plugs plus items without a problem so hose was definetely not the problem.

I will post pone this for October where the temps are going back to normal as it is not an urgent anyway to finish that now.

I released it with just pulling it up without any tool; came out fine (the plug) and the mold (with only a single layer) was ok everywhere apart from the vertical parts on the side which was where the main release happen. Over there was like with bumps on it.

Thanks

 

So, did the GC expand off the tool as the thing with less mass heated faster than the tooling?

Is sun hitting it thru a window?

A person can learn a lot here. But no gc experience, so I’m merely curious.

It sounds like the expert wants you to slow down the reaction, but you were trying to speed it or save on the AC bill.

.. interesting to say the least

 

No there was no sun into the plug through a window and of course I didn't want to save on AC bill.
I didn't put the AC on after spraying as I never had a problem with temperature before and didn't know that it might released in 3 hours at 30-32oC otherwise of course I will have it on.
From the mold that I got, the gelcoat is fine, not any problems at all on its surface. It seems like it is shrink from different parts of it on the most vertical parts (near the flange) If I describe it well.