gel coat help

General Composites Discussions Composites Talk
#1

Well I hope I am placing this in the right place.
I am rebuilding the helm of my boat and need to spray gelcoat over it. I have spayed the gel coat using 15% styrene to thin and 2% of that volume for catalyst. The gel hardens to the touch but if it is sanded it gums right up. so I cant get the orange peel out? This is a wax containing gel I am using. … Any help. Also for a finish coat once I get this right I may want to use Duratec? is it worth it or just deal with the orange peel?

Thanks for any help that can be provided.

#2

Temp or humidity can effect cure.

#3

I am doing it now in New england I am keeping the temp in the shop around 74 there is virtually no humidity. Again it is curing to the touch. feels very dry and no tack. but it is soft. you can easily gouge and scrape it with a fingernail after 24 hours.

#4

Did it spray too thin? The first time I gel coated I thinned it too much and it wouldn’t fully cure. 20% isn’t too bad tho I wouldn’t think although 10-15 is usually recommended. R u sure your not scraping wax with your finger?

#5

I am actually pretty sure I am not scraping wax with my finger. the test patch is not perfectly matched so once I scrape it I can actualy see the other color. I am going to do a test shot now.l I have the garage at 80 it is perfectly dry outside. I am going to thin only 10% and see what happens I am still going to stick with the 2% cat. If it is sprayed to thin will that prevent it from hardening? When I say thin I mean 10-12 mils not thin from thinner.

Thanks

#6

Yes, you need a certain thickness to have it cure properly. (0,4mm is a minimum, 0,8mm wet film thickness is ideal)

Also, when there is too much styrene present, cure is affected as well. Try thinning with 5 or 10% acetone, and spray from a distance (preferably with extractor) The aceton mostly evaporates when the material flies from gun to object.

You could increase to 3% catalyst if needed. Are you sure the gelcoat comes promoted (cobalt added).

#7

Two things spring to mind.

Firstly gel coat which does not have wax in it behaves very much in this way. But you do say it is a gel containing wax? When wax is added to gel it is often sold described as flocoat or topcoat and not gelcoat. It would do no harm to add 2 percent of wax additive. Test a small amount spread thin.

Second the wax already in the gel is entrapping the extra styrene which has been added, again surface will skin over but remain hardish but not cured as you describe. As herman suggests you could use acetone in place of the styrene if you wish to try spraying again.

Gel sands quiet easily I regularly use it as a cheap fill coat for plug making, brushing or rolling it on and sanding back. If it is not a big part it will take less time to sand flat than prep to spray and clean out your spray gun. You will need to sand and compound it anyhow even if you do spray.

#8

Some suppliers even give their topcoats the reference “gelcoat” usually followed by some obscure description, like “finishing” or “finition”. Very tricky.

#9

I did another test shot yesterday. Temp 70 degrees F no humidity o speak of.

I used 10% acetone to thin and 2.5% MEKP. This cured to a nice hardness. I will use this in the event that I cant get one last thing resolved. I have read to stay away from acetone as a thinner it causes problems where Styrene does not as it is already in the gelcoat.

Is it OK to use acetone or should I try again with the styrene? How about thinning with MEK?

Thanks
I shoudl post some pics it will be nice when finished. I just wish I took some pics when I began what a reck!

#10

If it is possible to get a little more help, I would be very grateful.

So first off I did not adjust my gun properly. Trial and error is nice way to learn but slow and expensive. I got WAY too much orange peel to be realistic. I sanded it down and reshot with the gun adjusted properly.

After wet sanding it looks like either the orange peel was still way to deep so I have these little spots and areas where it looks like again either I am not done sanding or… Could this be pinholes?

If it is pin holes cause it looks like for me to get these to go away I need to sand way too much what did I do wrong? How do I prevent them in a subsequent reshoot?

I did not thin with acetone I used 10% styrene with Brand new gelcoat.

2% mekp

Thanks
Bob

#11

No idea what it is, without a photo.

Perhaps this link is of any help, although it is geared towards spraying in moulds.

http://www.dsm.com/en_US/html/drs/gelcoatstroubleshooting.htm