Mold Stiffening Ribs / distortion

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#1

I will soon add stiffeners to a big mold (6X6’). I read about problems with local distortion because the new material (secondary bond) shrinks on top of the base layer. I am using tooling poly with something like 6oz/ft^2 as the mold base before adding the ribs.

Options:

  1. lay rope and cover with a few more layers of glass & tool poly
  2. egg crate it with plywood and construction adhesive
  3. egg crate it with plywood and glass it in (tool poly)
    1. or 3. with secondary bond and glassing done with epoxy

I want the best of all worlds; the mold as stiff as possible without distortion, and I don’t want to rely on expensive thickness. What are your thoughts?

#2

I would say #3 would work out pretty well

#3

Here’s what I ended up doing. Nice and stiff!