Saturday, February 25, 2012

Pre-cured sheet

I just finished my first attempt at pre-curing a topsheet and it turned out okay.

I bought 1oz surface tissue which is 1oz CSM matting. It has a small amount of binder in it but as it turns you out can't wet it out with a squeegee or roller without it coming apart. So I had to do some remedial work real time.

firstly , I masking taped some plastic film to a sheet of Perspex. Then, I painted a good layer of resin on the plastic to help avoid air bubbles on the underside of the first layer of glass. I figured the surface tissue would be thin enough to not need wetting out first. I've seen in a video RoadToRoad sent me that the key to a mirror finish is to put resin on the surface first, wet out the glass on a separate table before placing over the wet surface.

So I placed the surface tissue over the wet plastic film and poured 80gm of resin which should have been plenty but it seemed like it was only half as much as needed. I suspect the resin ratio for CSM is much higher. Anyhow, I placed the surface tissue down and poured the resin on. that's when I realised I couldn't spread the resin out. it pulled the surface tissue apart and the fibres balled up like fairy floss. So to fix it I decided to push ahead with the whole layup and hope the vacuum would be enough to push it through, which it mostly did.

So here's the pile from bottom up:
  1. plastic film stretched and taped on flat surface
  2. liberaly coat of resin on the plastic to reduce bubbles trapped under the subsequent layer of cloth
  3. surface tissue (I'll try to get some scrim next time which apparently is like fibre glass gauge and wets out easier.)
  4. graphics printed on tissue paper
  5. 4oz e-glass (next time I try wetting this out seperately)
  6. Peel ply
  7. let it cure under vac.
  8. painted white fill over the back. I used resin with pigment but I was wondering if painting it with epoxy spray paint might also work?
I worked the layup very hard with a roller. There were loads of air bubbles in the weave, so much so that it was like a resin froth on top. I suspect it was air in the CSM glass. I put a layer of peel ply over it all and smoothed it out by hand. I was thinking of just leaving it like that by after 15 mins the edges of the tissue paper that the graphics were printed on were still clearly visible. So I decided to put it under vacuum without any breather material because I didn't want to loose too much resin. I put a loop of felt underlay around the perimeter of the table surface so the bag needed to stretch down to reach the layup.

Vac bagging seemed to be the right move because only after sometime under the vacuum did it vanish. I'm wondering if this is because of the spray adhesive I used to stick it to paper to print on creating a barrier for the resin to soak through.

After it was all cured, the finish on the surface was good but it was milky in places which is from the fine air bubbles. Happy to say that the surface was void free so coating the surface with resin seems to have helped.

I then mixed up resin with white pigment (5%) and painted over the back with a foam brush and let it self settle.

Turned out well. Really flexible, check out the picture of it draped over the table. No concerns now about whether it will conform well with a 3D surface. There were some streaks for uneven thickness of the fill coat I painted over it to get the white background. This probably means that the resin was going off before it had a chance to self level out. It was a hot day so this was probably the cause. Next time I'll try a sponge roller and see if I can get a better result or maybe use gelcoat.


  1. Nice, Seems like the way to go to get a nice finished top of a board.

  2. Yes, I seems like the best option in the absence of commercial films. One cool thing is the possibility of texturing the surface. Fish scale imprint, the imprint of wood grain from vinyl tyles, I was even thinking that putting chicken wire down first could look awesome. The possibilities are limitless.