Hi guys, Help/Advice needed.

General Composites Discussions Showcase
#1

Hi everyone, I bought some cheap carbon cloth off a friend of a friend who was clearing his garage out, i taught myself the basics and made some flat sheets which turned out well apart from the 3 day cure time which I will discuss later. I have since done some race car body work at university which made me want to create my own molds and parts;I decided to try and and make a small part for my friends bike as shown in the photo.
](http://s1230.photobucket.com/user/Niebz/media/IMG_0122.jpg.html)[/IMG]

](http://s1230.photobucket.com/user/Niebz/media/IMG_0123.jpg.html)[/IMG]

I then set the part up ready to take a mold using modelling clay from easy composites. I didnt take a photos of the actual set up but imagine this all the way around.
](http://s1230.photobucket.com/user/Niebz/media/IMG_0126.jpg.html)[/IMG]

i then took the mold which left some messy edges where the clay was, but the finish wasnt too bad on the face that matters. There were a few holes which I filled in with some epoxy araldite and sanded.

](http://s1230.photobucket.com/user/Niebz/media/IMG_0127.jpg.html)[/IMG]

](http://s1230.photobucket.com/user/Niebz/media/IMG_0128.jpg.html)[/IMG]

The mold was sanded with 1200 as the final grade. and waxed with this.
](http://s1230.photobucket.com/user/Niebz/media/IMG_0134.jpg.html)[/IMG]

once laid up with 2 sheets of 280 gsm, one larger than the shape to do the walls, then one to fit inside, I made my first shaped piece of CRP.

](http://s1230.photobucket.com/user/Niebz/media/IMG_0135.jpg.html)[/IMG]

](http://s1230.photobucket.com/user/Niebz/media/IMG_0138.jpg.html)[/IMG]

As shown in the photos the part has a dull surface finish and air bubbles at the side.
I have suspicions that the following could be causing the problems.
-Mould not sanded to a fine enough finish
-Carbon un-peeling its self from the corners however without a vacuum i cant see a fix for this?
-No gel coat applied. When i went to do a layer of resin to let it set, it was repelled by the wax and wasnt even and grouped in puddles so i laid straight up with the carbon

  • Also there is resin build up in the corners where there is no carbon.
  • a cheap paint brush was used to stir it, which could be airing the resin mix with bubbles?

Heres a photo of my set up in my garage

](http://s1230.photobucket.com/user/Niebz/media/IMG_0125.jpg.html)[/IMG]

I had previosly used this epoxy resin for the sheet however it was quite expencive and also took ages to set properly, It cured in the living room balanced on top of a radiator never went fully hard like the polyester im using, it went gummy and flexible.
](http://s1230.photobucket.com/user/Niebz/media/IMG_0132.jpg.html)[/IMG]

So yeah, this is my first post, and my first carbon project rather than sheet. If anyone could provide any help or confirm my suspicions it would be muchly appreciated.

Thanks

Tom

#2

I would look for a vacuum pump on ebay… I got a nice one for less than £100 delivered from Germany. It actually pulls better than the easy composites one I have!

The fillet wax, I would use a good sharp blade to get a better crisp edge as that can help get air out of the corners or from the edges.
T cut or compound the mould to get the best surface finish you can…
Get some semi permanent release even the easy composites one is OK… Just get the smallest quantity they do as that will give you an idea of how well it works. Dont bother with wax. Use a gel coat. I get mine from east coast fibreglass… It has good clarity. I use polyester for all of my covers and it looks good. Plus it is cheaper to produce parts and learn how to make your parts. As for you technique in lay up… That is not something I can really comment on… But I would be tempted to say gel the mould and let it cure until it is almost cured enough to remove the tack on the surface… Just the lightest tack will do… Lay the surface down and wet it out really well… Then add the backing layers. getting air off the surface will be a bit hit or miss until you learn how the air gets trapped in that mould. I have two moulds that look almost identical and if I have a problem it is always with the same mould and the other comes out perfect. Each mould can have a problem on one area that adds a little work in lay up but once you figure it out. You will be fine…
Oh and buy some of the tongue deperssors for stirring sticks… It does help…

Polyester part in Carbon

#3

Hey Niebz, welcome to the forum. Looks like you’ve chosen a good part to start out with. First up, I would suggest making some moulds & parts with woven glass. I think it would help to get a feel for it an understand what is happening when you do a layup, since you can see air bubbles through the layers (and it’s a bunch cheaper than CF).

Looking at your original part you can see it’s a flat matte finish, so you can’t really be surprised that the mould looks the same… Depending on how important a high gloss finish is, you’ve got lots of options. Make a new part from the mould, then paint it & polish it to a mirror finish, then make a final mould. Or paint & polish the original part if you can. Or go ahead and polish the mould if possible (not sure how resins polish up though…) Or even just clear coat your part once you are able to make them to a standard you’re happy with. But somewhere along the way you will have to polish, any amount of sanding is just not good enough, it needs to be smooth as glass if you want a high gloss finish on the part.

Just an extra word of advice if you paint - do a test piece first. From my experience cheap rattle can paints just won’t do, it will react with the resin and pretty much mess things up. I would use 2k paint because it’s not chemically reactive (although it should still be tested).

As for the layup, for visible carbon it seems that the best thing to do it put down a surface coat of resin, then let that b-stage before laying up any fabric (that is when it goes tacky, so you can put a finger print in it, but you don’t get any resin on your finger). Once you get to that stage the fabric should just stick right to it no problem at all. Be careful because you cannot reposition the fabric once it touches down. A couple of tips I’ve read about removing bubbles from the surface coat is to use a heat gun lightly. This will reduce the viscosity and allows bubbles to pop, heat also speeds up the curing process. Another thing you could try is a light spray of acetone to remove bubbles. Haven’t tried that one myself.

You really shouldn’t need a vacuum… if you’re having problems with fabric bridging you need to solve that problem first. Vacuum is used to consolidate the layers, not to solve layup problems…

For your wax & the surface layer of resin: sounds like maybe the wax was not applied correctly, or could just need to try a different wax? The wax release I use is in a liquid, you rub it on and then use a clean cloth to rub it before the solvent flashes off. You shouldn’t have any visible wax - it will be there, buy you shouldn’t have any streaks etc.

Or it could also be the resin… maybe too runny. I found that epoxy is much better suited to surface coats than the polyester I use. Seems to have a better surface tension and wet film thickness. There’s lots of variables…

A paint brush to mix the resin sure won’t help with bubbles. Tongue depressors or even paddle pop sticks are the way to go.

The epoxy you used for the sheets definitely didn’t cure properly. Did you buy that new? It sounds like it’s either well past it’s use-by, or wasn’t mixed in the correct ratios? I would check the data sheets, with the fast hardener like you have it should be well under 1 hour cure I would guess.

One other tip with your layup - maybe the sides of your part need to be extended a lot more? This will allow the fabric enough area to settle properly and should help with the bridging problem. That way the fabric won’t curve over and just come to an abrupt 90º angle. Basically - increase the distance from your original part to the glass.

Hope that helps, have a look around the forums as there’s plenty of info here to be learnt.

Cheers!

#4

Great, thanks for the informative replies guys. I was using the polyester resin as a top layer however I will purchase some clear gel coat today. Also planning on making a new mold. Il have a look for some new release wax/liquid. The resin looked it had a hydrophobic effect with the wax where it puddled together on top.

As for the epoxy I rang the company and they said I was doing everything fine and to send the epoxy back for them to test. I stupidly went through 2 lots of the epoxy so it wasnt out of date. I should have sent it back however when I was using it I just let it cure for 3 days as I wasnt in a rush and I was a full beginner and didnt know what to expect.
If anyone wants a go I will post some out for you to try

#5

Guessing you bought from Easy Compisites… I would suggest to get started you practice using all polyester resins… It gives you a lot lore parts for the money and you will see the results of your work and you can make small changes to your technique to improve your parts without it costing a lot of money…