Composite layup information - Gelcoat and Epoxy

[befu]

OK, this one is about laying up your own boats. I have been playing with getting polyester gelcoat to work with epoxy laminate. I know, it doesn't work together, but I want to know why or just "how" doesn't work together it is.

So i laid up a small hatch and did different treatments on it to see what happens. then ripped it apart and took a video of it.

Something has to work. What are others doing. Europe claims that polyester resin isn't any good and it must be epoxy. But they are putting out boats that have a nice white outer shell. What are they using? All of the epoxy surface coats are rather thick and must be brushed on, not sprayed. But if you look at the light layups, the white really looks nice and consistent, like it is sprayed. so, short on information, I just plow ahead learning as I go. I have found one company in England that makes a polyester gelcoat specifically for epoxy layups, but not sure where to buy it. Seems like they are more geared towards industrial users and not someone who wants 1 gallon!

The test: Gelcoated a simple mold, let cure for 24 hours at about 70 degrees F. I then greensealed the gelcoat and let it set another 2 days, or 48 hours. I then cleaned the green seal off and treated the polyester 4 different ways. 1. just washed off, 2. greenseal scrubbed off with green scotch brite pad, 3. gelcoat lightly sanded to remove gloss, and 4. washed the gelcoat down with acetone. I then layed two layers of 6 oz e-glass on with laminating epoxy resin. that was two days ago, so this evening i tore it apart, not quite two days later.

Well, so far a Acetone scrub seemed to work ok. I do not have a tensile tester to really do a proper test, but I could fabricate something I guess.

so, what do others think of the test and results? What do others think Europe and China are doing to get a gelcoated boat hull made and maintain quality?
any ideas of other things to test?

thanks for watching, Brian

[jcald2000]

Start here with the "sticky" at the top.

http://www.rcgroups.com/composites-fabrication-210/

[tiqueman]

Brian the Engineer... ahh thats great. I hate when I round bouy 4 and someone hits my boat w/ a hammer. Seriously though, Did you use waxed or non waxed gel? Waxed will continue to release wax to the surface, even after sanded. I learned that when I worked at a marina and used to help the detail/ repair guy work on boats when we were slow. Anything you do to a gel surface has to be done immediatley after its been sanded. Ive been told elsewhere, that is one of the reasons gel seperates from epoxy over time. Non waxed you should have greater success with.

Heres my question... Polyester resin (gelcoat) will only stick to polyester, but its said that epoxy will stick to either with proper prep. That being said, I do not know why if you put gelcoat down in a mold, and then followed it after its cured w/ a prep and some epoxy why it wouldnt work? BUT, thats said it doesnt work or last.... why? BUT, it works w/ a bonding agent as you and I discussed earlier today???? Ive never experimented as you are, so Im curious to see what happens.
Ill be watching to see what you come up with.

[befu]

Thanks for the link j. Will start doing some reading.

tiq, my gelcoat is a non waxed resin, so nothing in it to rise to the surface. That is why I coat it with the greenseal, to get the last layer to cure. If it is fully cured, clean and not shiny, the resin should stick. Everyone says to use epoxy to attach stuff to the inside of the hull. Maybe that is it.gelcoat and hen a coat of polyester resin. Then green seal it,sand and laminate with epoxy.

Hitting the boat was my only option. Unless you want to send me your hpr so I can hit my hatch with that!!!!

Engineers are a funny breed huh?

Brian

[raptor347]

The best finish I've found for an epoxy layup in spraying PCL Polyprime in the mold first. Polyprime is a high build polester primer (think feather fill or any of the other common polester auto primers).

You get a great finish (as good as the mold surface can provide) and the surface that you do the layup against is a porous mat finish that the epoxy really sticks to.

Polyprime is one of the few I've found available in white.

If you're looking for a pinhole free paintable finish, any of the polyester auto primers will work.

[befu]

Thank you Brian. You mention the featherfill and I was wondering about something like that. I remember using that back at Western Michigan when I did the 93 solar car while attending college. It was a sickly yellow color, so I will look into your recommendation, the white would be better.

I think I am going to try a couple with the gelcoat wiped down with acetone after curing under greenseal.

I also need to order a couple of outrunners to make a snow cat now after seeing that video!

Brian

[befu]

Just got my epoxy gelcoat in, so I think I will start playing around with that. $65 a quart delivered! Can't believe to many companies are using this stuff on cheap hulls!

since it is basically epoxy that is thickened and has additives, I wonder if it could be thinned some with epoxy resin?

Brian

[befu]

next installment: This one test two hatches that use epoxy surface coat with USC laminating resin, same ole destructive testing method!

Actually, it worked pretty good. I think I am settling on the epoxy surface coat thinned by 10% with laminating resin. Spreads easier but not real runny, and it seems like it was slightly more flexible than the pure surface coat.

Anyways, here is the next video. Oh, I also have a sinus infection, so no my head is not in a bucket while recording this.

Brian

[tiqueman]

What surface coat did you get? Im using the Adtech 201 epoxy room temp surface coat. I was told my Adtech NOT to thin it as it weakens it.

[tiqueman]

never mind, just had to watch the vid

[tiqueman]

I was also told by Fiberglast not to thin it. That was from their techline, I think the guys name was Mike.

[martno1fan]

You can buy specific epoxy gelcoats nowadays.Ive never used it as all my hulls are good old polyester and theyre strong hulls too ,epoxy is hazourdous to health so i wont use it.
Mart
i get my materials here theyre offline for maintenance but check the gelcoats out when theyre back up.

http://www.ecfibreglasssupplies.co.uk/

My Website

http://www.waveridermouldings.zoomshare.com/0.html

[DISAR]

I have been experimenting with gel coat,polyester,vinylester,epoxy as well. What I realized is that polyester gel coat does not work well with epoxy, eventhough I have made one boat using this method and came out really nice and nothing has happened to it and the boat runs at 60mph. What I did was polyester gel coat applied by brush and quite thick layer, 1 day after sanded it and applied the epoxy with fiberglass and carbon kevlar. No detachments at all. However I tried the same method in hatch and there were detachments of gel coat, so I never tried it again.
Thereafter, I use polyester gel coat with polyester or vinylester where the bonding is guaranteed for the first layer of light fiberglass 50-70gr, after that I lay out another fiberglass with poly or vinyl while the first coat is still tacky and in case I want to use carbon-kevlar or carbon kevlar I use epoxy which impregnates(?) these clothes 100%. I let it cure for 5-6 days very good sanding with 80 grit and then apply epoxy with these clothes.
Generally for boat-hatch making I prefer vinylester which has good mechanical properties and reasonable cost. Epoxy has better properties but the cost will increase taking into account the epoxy gel coat especially for big boats.

[martno1fan]

I allways do 3 coats of poly gelcoat in the mould,lay my glass cloth layer while its tacky after first filling all strakes and chines ,corners etc with a bog mix of resin and fibres.Once this layer of cloth is fully wetted out i then add one layer of Carbon if im doing a carbon glass layup,wet on wet this saves on resin and cuts the weight down considerably.Heres one i did for a forum member just last week,total weight of the hull is 10lb,not bad for a 58" hull with zero twist.My glass only layup is different but same weight and still very rigid.Havent felt the need to go epoxy nor do i want to i hate the stuff,vinylester is even worse to work with no thanks.

[DISAR]

Nice, what are the weights of the fabrics you used? One glass and one carbon? Poly is ok, I agree, the working time is an issue but I found a "delay liquid" which allows to use it for 1 hour. Here is a 54" cat that I made.