Molding my doors

General Composites Discussions Composites Talk
#21

So some issues are already becoming apparent…looking underneath through the glass panel, the gel coat is not sitting smoothly against the glass. It looks like it has pulled up and looks like a topographic map of mars:(

Also, after laying down the black gelcoat (I waited til the orange was tacky but would not pull away on a gloved finger), I noticed this:

It looks like the gelcoat is kicking too fast?? My current conditions are: 67* and 89% humidity. I’m measuring everything with digital scales and mixing the MEKP just between 1.5 and 2.5% per the mfg directions.

#22

i think that the main reason that you saw this problem is the second layer of the gealcoat and it has trap some humidity between layers, i don’t understand why you chose to apply more than one coats:confused:

#23

How thick did you apply the gel coat? Did you brush or spray, 20 mils is the typical recommended thickness.

#24

The first coat was too thin…I could see through it pretty much everywhere. I mentioned several times in this thread that I was planning to lay down several coats of gelcoat and no one said this was a bad idea. Even the mfg directions say it’s acceptable to lay several coats.

I’m just looking to trouble shoot and learn…not trying to be defensive. Thanks for the input.

#25

Gel coat was brushed on.

#26

So, with a touch test it was obvious the gelcoat wasn’t even attached to the door anymore…so I just peeled it all off.

I don’t think the issue had anything to do with having a second coat of gelcoat, because you can see in this pic that even the first coat of gel coat had lifted.

#27

I would love some help figuring out what went wrong so I can try again next weekend…

#28

that shrinkage - crocodile skin occurs because of:
the high humidity of the environment
the low temperature
very thin (first) layer of gelcoat
the wrong percentage of the catalyst which leads either in insufficient hardening or in very long period of hardening and you apply the next layer too soon because of that.
i’m guessing it’s because of the humidity that did this to your mold and ofcourse that shrinkage couldn’t just happen only in the second layer, i would suggest to brush one thick coat of gelcoat (mix it VERY well before usage) and proceed with the resin-fiberglass but wait some more advices from the most experienced

#29

I used a cheap digital scale to “roughly” calculate 1.5 to 2.5% MEKP by weight. Are you all trying to be perfectly accurate with the MEKP or being within that range close enough?

It has rained here everyday for the past 3 weeks…the humidity is out of my control:(

#30

Humidity does play a part, you will find a combination of high humidity and thin film thickness of the first coat, has caused this to occur. The thinner the gel coat you apply the higher the catalyst percentage should be. Minimum requirement for the first coat should be approx 20 mils (0.5mm) I would then only apply a further coat by ensuring that your catalyst level is still on the high side if it is required! Do not over apply as you will run the risk of pre-release, prior to lamination. How old is the tooling gelcoat? If it is old then your problem may be your gelcoat is not achieving thorough film cure, as well as the other factors listed above.

#31

If you want you can send me a pair of those doors for testing. :slight_smile:
I can only imagine the amount of work that went into making them.

#32

I can start to understand…:frowning:

#33

Thanks! I’m gonna study the MSDS to try to understand exactly what went wrong.

#34

Just brush one layer of the orange gelcoat, not to thick, but a closed layer of about 0.5-1mm. Than wait until it starts to gel and put a lot of cottonflocks on the backside. When it is cured laminate with epoxy, but put a mixture of epoxy, thixo and cotton flocks in the corners. Maked it easier to laminate.

@extreme: you can buy a pair of the doors. We made the whole bodywork for the 355.

#35

Hehe, indeed elephant skin. Undercure of the first layer.

Make sure your first layer of gelcoat cures properly.
-temperature
-humidity (seldomly a problem in NL, so not too much experience with that)
-layer thickness
-MEKP level.

Eyeballing MEKP levels is not going to get you there. Buy a cheap scale for measuring your resin, or use mixing pots with some indicator on them. Use a squeeze bottle for your MEKP. That are the cheapest options to be accurate.

We sell squeeze bottles for 3 dollars, and give them away when someone orders 5 kgs (10 lbs) of polyester resin. Giving away the bottles is cheaper than answering the Phone because something went wrong.

#36

Sorry to see the problems you had with the gel coat. That is exactly why I asked if you weren’t worried about having such thin coats…

Oh well, live and learn. I bet you won’t make that mistake again!

You’ve got a Ferrari F355 to test them on? Lucky guy!! :stuck_out_tongue:

#37

do you mean to pour dry cotton flocks? could you please explain what this trick helps you with ?
thanks

#38

Thanks for the help! I’m not sure where to find the cotton flocks but I’ll do some searching.

Thanks for the help! I mentioned above that I have cheap scales, when I said “eyeball” I meant that if I weighed out 204.5 grams of gelcoat I’d add approximately 4 grams of MEKP to yield a 2% mix ratio. I used the word eyeball because I didn’t pull out the calculator and get an exact figure for the MEKP.

In the future, how can I quickly cover such a large surface area with gelcoat? It literally took 45 minutes and 4 separate batches of 200 grams of gelcoat to cover the area. I trimmed the tips of the the china bristle brushes with a pair of scissors to aid applying the gelcoat. Any other tips for uniformly covering such a large area quickly?

#39

I can’t see the pictures for some reason but by the sounds of it I had the same problem with my tooling gel coat “aligatoring”. Herman also gave me the same advice and have not had a problem since. Now I go toward the higher side of the catalyzing percentage, give more time before layup, and brush it on a little thicker. It also helps that its summer time so temps are helping me out as well. Good luck with everything.

Also, why can I not see the pictures?

#40

I exceeded my bandwidth with my free photobucket account. I’ll upgrade tomorrow.

Thanks for the help! So you catalyze at 2.5% MEKP…when do you apply your first layer of backing? When it’s slightly tacky? Or do you wait even longer (12 or so hours) before applying the reinforcement?