I have just put a couple of layers of UD carbon fibre onto the top tube of my bust MTB frame. I wetted out the 2 layers then applied a release fabric and then a breather layer and then vac bagged (25 MG). The breather fabric was also wetted right out.

I have just unbagged and removed the breather fabric, but the UD looks dry and I wasn’t able to sand it smooth. When I sanded, I could see small strings of carbon fibre. In the end I ended up sanding it all off with 80 grit back down to the underlying 12k weave.

Is UD difficult to work with as I was hoping I would be able to sand it like I can the 12K stuff so I could get a top class finish.

It had been vac bagged for 24 hours.

Not used UD stuff, how thick was it(weight i mean)? When i’m laying up fabric i like to try an put a layer of resin then the fabric and try to force the resin through the fabric before wetting out.

Did you put the whole frame in a bag? Just recently fixed a frame and used shrink tape and breather/ release fabric as to vacuum bag would need the whole frame in a bag to stop air being sucked through the tubes.

Two layers isn’t very much, especially if you’re vac bagging it. You probably only had the thickness of the two layers, so no much. I’d do it again, but once cured, apply some more epoxy as a layer you can sand down, without taking off the carbon.

Not used UD stuff, how thick was it(weight i mean)? When i’m laying up fabric i like to try an put a layer of resin then the fabric and try to force the resin through the fabric before wetting out.

It was lightweight, can’t remember the g/m2 figure. I did exactly as you state. Just vac bagged the area in question by using that double sided vac bagging gum tape. Full vac was obtained with no air ingress.

Two layers isn’t very much, especially if you’re vac bagging it. You probably only had the thickness of the two layers, so no much. I’d do it again, but once cured, apply some more epoxy as a layer you can sand down, without taking off the carbon.

It isn’t structural but more a decorative finish I am trying to achieve. I prefer a UD finish to a twill.

Just wonder why although I fully wetted everything out nicely, the UD just looked dry when I unbagged everything. Just not seen that effect before.

On reflection I wonder if it was because I forgot to put a layer of release film between the peel ply and the breather fabric and as a result the epoxy would have migrated through the layers into the breather fabric?

I normally just use peel ply and breather. If the carbon was stuck, there was epoxy around the fibres, just not enough to sand down.

I normally just use peel ply and breather. If the carbon was stuck, there was epoxy around the fibres, just not enough to sand down.

Ok. SO it sounds like omitting the release film was not the issue. I might give Easy COmposites or EC Fibreglass a buzz as I am a bit lost with this one.

too much vacuum, pulled too much resin out of the cloth.

too much vacuum, pulled too much resin out of the cloth.

Ok. Thanks. I’ll try again with reduced vacuum.