Gelcoat issue & first attempt, please go easy.....................

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#1

Hi,

First of all thank you to everyone who has replied to my previous requests for help, using what I have learned so far I have had a go at infusing and apart from the obvious in the attached picture, 90% of the part has the exact finish I was hoping for.

Yesterday I applied a coat of polyester gelcoat to a crude mould I machined quickly in work. I applied this as best to my ability and let it cure for around 4 hours before I laid in a 300g fibreglass mat, then a 2mm soric mat, the a final 300g fibreglass mat. The mould surface is perfect and not at fault, that would be me of course. Infusion took around 8-10 minutes for the record, the soric flows quite quickly however I may try some combination mat soon to compare the speeds.

The part is around 600mm x 300mm and is only a test piece.

The gelcoat if anything seemed like it wasnt as tacky as I would have expected, however when I started to lay the first layer in this did stick nicely to the surface. The part was infused with polyester resin and left to cure for around 20 hours before I removed the bag and pulled it from the surface I cast it against.

I am wondering if anyone can advise what I did wrong please? I am guessing that the gelcoat thickness was a problem here (too thick or thin) or hadn’t cured long enough before I infused. 4 hours did seem a little too quick however I had to get some progress made by today and it is only a test part. The pattern seems to be ‘sucked up’ at this location if that makes any sense to anyone?

If anyone has any ideas I would really appreciate any comments. I am due to test another piece later today and will be sure to either wait longer or try any suggestions others may have.

Thanks again for everyone’s support.

#2

Looks like the gelcoat was applied too thin. This might have caused undercure as well.

Also possible is that the mould trapped styrene in that corner. Put the mould on it’s side while curing.

#3

Cheers B, I think I may have been a bit shy in the corners on my haste and excitement!

I’ll try a few other things on Monday and be more careful.

Thanks.

#4

I’d guess too thin gel as well. 4 hours should be way more than enough time. In fact, I regularly laminate after about 30 minutes. What was the level of MEKP that you used? Should be between 1% and 2%.

#5

Hi, it was 2%

#6

Where the gel coat is thin the vacuum can suck it off the mould surface and into the hollow part of the soric.

Thicker gel coat has more strength.

#7

Sorry I didn’t get back to this sooner. Unless there is something special about your gelcoat, at 2%, you should have a good cure in 30 minutes or less. Based on my experience, I’d say your gel in the problem area is too thin, maybe 8-10 mils. That is thick enough so you don’t see gators or resin leaks but not thick enough to cure well.

#8

4 hours is too long for 2%,like the others say,30 mins should be dry to tack.