Problems with gelcoat and hand laid fiberglass lamination

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#1

Hey guys,

I have a degree in Industrial Design and have been dunking my feet in the composites field during my spare time.

Over the past two years, I have developed a rear spoiler wing for an rsx:

negative mold locked together:

negative mold all apart:

I want to first try casting these out of hand laid fiberglass.
I lay them up with the two large halves bolted together, and then lay up the mounting pods seperately and then pop the pods into their registered spots, wait for it all to cure and them take all the molds off.

As you can see, I never have any trouble with the tooling gelcoat, I brush it on and it works great everytime- even in colder weather.

My problems always begin when I am starting to cast the spoilers from the mold.

First problem is this white gelcoat I have been using. I dont own a compressor or anything like that, so I brush my gelcoat on using a foam brush…which actually works well and does give high and low areas which a normal bush gives off.

I then wait for it to get tacky, no fingerprints and then usually start the laminate layup.
I have a friend who said I should try and laying down a later of just resin and letting that cure to put a barrier between the gel and the laminate, buuuuut I was hard headed and was rushing so I started with the laminate right away.

As I started to wetout the fiberglass, over time I started to notice that the white gelcoat would come off on my brush and in tighter areas I could start to see the orange showing through from my mold. What causes this? xxxxty quality gelcoat?

My other problem is the lamination of the tight rolled edges around the perimeter.
No matter how many times I go over the edges with my brush, and corner roller, the glass just ends up pulling away from the tight edges, which I know will leave me with brittle air pockets that will just break through after the part it removed from the mold.
Also, I find that white gelcoat is very hard to see air bubbles and such when laying up on top of it, compared to orange or black gelcoat.

I dont know much about using compressors or vacuum bagging, other than doing some basic stuff for a wood class while in school.

Any help would be appreciated!

#2

first off are you using polyester resin or epoxy, i’m guessing polyester since ive never seen orange epoxy gel coat. When i would do a gelcoat mold or part i would first put it on and let it gel till you could touch it without leaving a finger print. You seem to be doing this step. Next I would apply a thin layer of resin down on the surface then a thin layer of glass and let that sit overnight. I vacuumed bagged mine down with low pressure and with a piece of peel ply covering the surface to help soak up the resin along with getting my surface ready for the following plys of glass. You probably don’t need a vacuum to get this job done but it helps.

#3

So then after applying the glass layer and letting it cure you add the structural layers? Do you have any issues with delamination with this method? Is this how it’s done for higher performance parts as well?

#4

yep, I am using polyester gelcoat and resin. My main problems are in the filleted edges, I guess I will just have to use long strands of fiber and glass them in first before trying to use csm over the edges.

To answer kayakdudes Q: yes you have got it correct, but just make sure to properly rough up each cured layer before addding a lew layer on top.

#5

use choppies around the sharp corners, (choppies are chapped strands that are not bound together or weaved, the are short in length and as such will go into tight corners easily. This will help with stopping air voids in the tight corners.

#6

Another Honda guy :smiley:

#7

ahh, thats what I was thinking of trying out. Would it be best to just order a container of this stuff?
I found this:

http://www.defender.com/product.jsp?path=-1|10918|12212|309318&id=17815

yup yup! I mostly would post on fiberglassforums.com, but I recently found this site.

#8

No i have no delamination problems with this method, but then again i’m using epoxy resin, and the part isn’t fully cured yet. I only use this method for when i’m building molds, all my parts are either painted or not painted.

#9

I use a thick mix (semi-hot) of gel-coat and high-5 and brush in the small radius areas. it smooths out the tight corners and likes to stick to the matting