Anyone ever had problems with gelcoat sticking?

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#1

I have been doing some flat panels recently using poly spray gelcoat and poly/vinylester infusion resin. Normal carbon twill layup etc, b stage gelcoat then infuses fine no probs.

Even if I postcure the panels, the gelcoat on the cut edge after I machine them just kinda flakes away. You can get your nail and pick it off. It should bond together super well but I cant send stuff out like this!!!

Previously I have mostly been using duratec high gloss clear surface coat/epoxy resin on panels, no problems at all when it gets cnc machined… The only thing is epoxy takes forever to fully cure literally a few weeks when its colder.

Has anyone experienced anything like this before??

Its pretty cold here at the moment but I try to keep the shop warm so I cant see that as a problem.

#2

too much catalyst can cause brittleness, might want to experiment with that…

#3

its not so much it being brittle but not sticking very well to the top laminate layer. Its fairly brittle anyway if you have it too thick, I have tried under catalysing and over catalysing it but it still does the same. When I use duratec clear I dont get the same problems which is strange so I dont think its my infusion technique.

Have tried using different kinds of gel coat aswell…

Does anyone on here do any production cnc routing of carbon? The only way I can get carbon fibre to cut very cleanly is either prepreg (v expensive but perfect everytime) or epoxy/carbon infusion but left to fullly cure + then do a postcure (v expensive and takes longer)!

#4

I would think one or all the following problems.

1- waiting too long to infuse the part, the gelcoat is cured too much and the two resins aren’t chemically bonding together.

2- the infusion resin isn’t reaching the gelcoat, How thick are the panels?

3- the resin and gelcoats aren’t compatible

#5

its definately not letting the gel coat cure too much, I just let it b stage then infuse within an hour or so.

As far as compatability goes not really sure but I would have thought a poly gelcoat would pretty much go with and ester based resin.

The one thing I noticed is when I pick some gelcoat off the surface it does actually look quite dry underneath on the outer carbon layer. The surface is absolutely flawless though through the gelcoat and doesnt look dry!! Panels were only 2mm thick and I dont infuse them quickly.

Could it possibly be that the resin im using isnt fully combatible with the carbon? anyone have these kind of problems?

#6

what`s the brand of “poly spray gelcoat and poly/vinylester infusion resin”

#7

the gelcoat is made by cray valley and the polyester resin is a thin infusion blend made specifically for me by delta resins.

I am just doing a few tests using poly gelcoat and infusing an epoxy resin + another but instead of a gelcoat I sprayed down the poly resin surface coat and will infuse it with poly resin and see how that comes out!!

#8

Do somethink else,

when the gealcoat is cure take a small soft paper and put Aceton on it. Get to the mold and clean it up with this paper (Not to take it out but to make the geal coat stickie).Put the carbon (be careful when you install it) and all the rest layers and then start to make the infusion. With this way your geal coat is stick and you have more possibility to have better results.

#9

I believe most carbon fabrics are “sized” for epoxy , poly just doesn’t bond to the fibre well enough , use Vinyl ester if you want to stick with non yellowing resins.

#10

The poly is more faster, more cheaper but the vinyl is little strange resin. I am using it only in the Carbon exhaust system.

#11

i have used vinylester on carbon but because it’s dark in colour its easy to show up in corners etc where the resin gathers :frowning:

other than that, it makes strong and flexible parts!

#12

newbie question, why are you using gelcoat? why not just use full epoxy or poly resin?is it clear gelcoat and did you ever find the problem?