Bubble elimination - Vacuum Bagging

General Composites Discussions Composites Talk
#1

New user here.

I have a couple questions. All the products I have been using were ordered from fibreglast.com, except for the fabric which I got from AVT…

  1. What is the best way to work out the bubbles and voids in a wet layup (6oz CF Twill in Polyester resin with a clear gel coat)? The last time I tried, I had pretty good luck with spraying the gel coat, letting it get tacky, then brushing in the PE resin with a bristle brush, placing the fabric, then applying more resin with the brush, then vacuum bagging. However, there were still some very small bubbles. Hardly noticeable, but I’m a perfectionist I guess. Another drawback was that the vacuum bagging seems to have distorted the fabric a little bit where it was pressed up against the gel coat ‘orange peel’ texture. Any tips? Is there some type of squegee or roller I can use to work out the bubbles? Yesterday, I laid up another part using a little different technique. This time, before placing the fabric, I painted some resin onto the gel coat. Then I laid out the fabric on a sheet of vacuum bagging material and brushed the resin into both sides prior to placing in the mold. Once in the mold, I placed the bagging mat’l over it and used a plastic squeegee to try to work the air bubbles out to the outside of the mold. Don’t know if this was successfull yet - I will be releasing it from the mold tonight.

  2. Is there an epoxy surface coat that is clear? If not, would a polyester gel coat bond to a part laid up with epoxy? I’m thinking about using the clear pe gel coat as a clear coat for UV resistance. Spraying it into the mold first, and then laying up with epoxy. Would there be a better approach?

  3. What epoxy resin/hardener combinations is the most clear (I.E. least amber tint)?

Thanks so much for your help. I’m just getting into the industry and can use all the help I can get!

Sincerely,

Jeremy

#2

If your trying to get air out of your layup I would recomend using .015" perferated release film vs. peel ply. If you really want to use peel ply (for finish reasons) then use release film as the immediate layer after your peel ply. Its much easier to roll air out of a part when your using release film.

I think your wrinkles may be caused by laying up a little too early in the gelcoats “B” stage. Also be extremely anal when it comes to pleats and overlaps with your peel ply. It can cause a lot of wrinkles and resin ridges.

I use fast epoxy as an epoxy surface coat. Use it the same as gelcoat in terms of “b” staging.

#3

A laminator that makes parts for me is able to make perfect silver Eglass parts, using hand lay up. No bubbles, no hassle with bagging, and far quicker production time for each part.

#4

I’d say they’re less like wrinkles and more like dimples - as if the fabric is distorting to conform to every little imperfection in the gel-coat surface which has some orange peel. In this case, the gel coat has cured completely prior to infusion. Should I run the infusion earlier in the ‘b stage’ so that the vac smears out and eliminates the gel coat orange peel?

Maybe the real question is how to reduce or eliminate orange peel in the gel coat… I’m using a cup gun with 2.0 tip. Higher air pressure? Thinner? How much? What kind? I’ve heard of using styrene, acetone and ‘fast’ laquer thinner… Which is best? How does ambient temperature and humidity affect the gel coat spray? What are the optimum atmospheric conditions for spraying gel coat? Can I fit any more questions in this post? =)

Cheers,

Jeremy

#5

Jeremy, every little imperfection in the gelcoat will show up as a distortion in the weave pattern even a dust spec will show. The gelcoat must be smooth, i use Duratec clear this is slightly thixothropic and as long as you do not spray it too thick will not run. Duratec flows out to leave a completely smooth flat surface, i thin mine very slightly with acetone with no detriment to the final cured hardness. If there are any dust nibs you can flat these off with some 400 wet or dry use dry, don`t worry that you have destroyed the glossy surface when doing this as it will not show in the final part. Let it fully cure i.e no finger print when touched, then use a little mist of 77 tac adhesive to hold the cloth in place.

Baz

#6

Would using less hardener in the gelcoat eliminate the orange peel effect? Speaking of automotive painting ( something I know much more about than composite work) orange peel is a result of too high of ambient temperature so the paint doesn’t have time to lay out smooth, spraying on the coats too thick, or possibly too much hardner mixed in. Does this theory also apply to gel coat spraying?

Also, please don’t be hard on me as i’m new to this as stated many times. Why use gel coat for cf parts? Isn’t epoxy what is used instead of gelcoat for cf work? I’ve heard epoxy comes out just about perfectly clear with no to little visible tint on the finished part? These are probably newbie questions i ask here lol. Gotta learn some how, right.

#7

You spray the PER gel coat (clear) into the smooth mold and that ends up like an eggs shell. As long as the mold is perfectly smooth, the part will be also as the mold is a reversed copy of the part. If you brush the PER gel coats into the mold, you will have highs and lows which distorts the view.

Epoxy will yellow over time as it doesn’t have the UV inhibitors as PER.

But the best UV is PUR clear automotive paint applies after the composite part is made and removed from the mold.