I´m having some problems with a couple of molds i made. They have leaks! They are quite big so making them again it´s out of question. (or at least would be my last option). Envelope bagging would be a huge waste of material for the same reason (big mold)
I´ve seen some post on infusing the back side of the mold to fix this problem. But how is this done? Is some extra material applied on the back? Only brush resin and then pull vac on that?
Thanks in advance for any help
See attached. I have not personally tried this but looks pretty straight forward.
Where did you take that pdf from? don´t really know what kind of products they are talking about.
thanks!!!
PTM&W is a California based company that sells mold making supplies. You should be able to get similar results with normal infusion epoxy, the lower the viscosity the better.
i have polyester infusion resin. since the resin of the mould is polyester maybe will be a better option. and i think it has less viscosity than the epoxy that i use for infusion
Polyester is a bit brittle and doesn’t have really good secondary bond characteristics so I’d say it probably wouldn’t be good for the type of process described in the PDF. That being said, I’ve talked to people that use regular latex paint on the back side of their mold to seal leaks. Never tried it myself but it seem like a reasonable idea (and it’s cheap too :D).
well, i did try that method of the pdf but no success 
You could try to place sealant tape and economy ply bagging material to seal just the contact or flange areas of the entire mold. That may work, and would require much less bagging material than a large envelope setup.
It´s quite big the mold, and the underside it´s touching the floor when infusing so the bag would probably leak after one or two infusions
What is the size of the mould? Is it so unreasonable to envelope bag for the first infusion and allow that to fix the leaks, and from then on you should be fine to follow standard procedure?
I envelope bagged it on the first infusion but it didn´t solve the problem.
It´s an hardtop so it´s not huge but it´s quite big
I see. Are you absolutely sure it’s the mould leaking then? Every time I’ve ever had a mould with porosity, the resin leaks out the back and seals everything up. I don’t see how you could have a leak in the mould and not have it fill with resin when you infuse.
i think it´s a very small leak and resin can´t get there. I´m sure its the mold.air is coming from the middle of the mold and i have tried more than once and the leaks are more or less always on the same place.