Porous Mold Tool issues

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#1

Hi, was wondering if anyone has any suggestions regarding the repair of the back of a mold tool which was made out-of-autoclave. The tool is porous throughout and there is was little vacuum integrity when surface bagged. I have coated underside with epoxy resin to try and seal and this has helped me achieve a higher vacuum pressure but still it wont hold vacuum? An envelope bag is out of the question due to the complexity of the underside ( contains rib structure).
I have considered wet lay-up of dry glass underneath but not sure if this will be sufficient or if there is a quicker, cheaper and less labor intensive alternative? I need to re-use tool multiple times and cannot afford to scrap and start again.

The tool loses vacuum pressure in line with temperature ramp ups so thermal expansion is playing its part in aiding the loss of pressure which suggests porosity is still inherent.

#2

Are you sure your vac system is ok ?
Do you have other parts going through ok ?
If you want to really seal the back remove the backing structure,abrade the surface,bag up on your mould surface and resin coat the back and let the vac pull the resin in
How big is the item ? Envelope bagged plenty of wing/bodywork moulds 6/8/10 ft long
Not nice to do but is doable
Do a double bag so you can try an get 3/4 cooks out of your back bag
Breather can stay on the back for LOTS of cooks

#3

Yes vac system is good mate. I do use for other components as well and no problems. Also connected it to a stand alone system which proved no different. The backing structure is bonded on so removing is not an option, especially as the tool is roughly 5m x 3m. The underside of the tool was covered in peel ply which was removed when the epoxy resin was applied. A surface bag was also under vac to draw resin into any pores. An envelope bag really is out of the question as there are trolleys connected underneath which inhibit full coverage as well as the strengthening ribs being in the way.
Maybe attempting a double (back)bag which stays on through the 3 cures required per component is not altogether impossible…difficult but maybe not impossible. Was hoping to find a more permanent solution though, one that once applied would not need thinking about again?