> Here’s one for you aerospace guys.

> Can someone explain to me the vacuum bagging process. I know that the home
> built airplane guys use it a lot to get maximum strength/weight ratios out
> of a given thickness of cloth.

> As I understand it you apply the glass and epoxy in a normal way cover it
> in a “peel/ply” and/or “breather” layer, put the whole thing in a vacuum
> bag and then by evacuating the air, you get uniform pressure over the
> surface. My assumption is that less epoxy can be used and still get
> complete wet out and bonding to the surface.

> My questions are:

> 1. how do you peel off the layers after the epoxy cures? I remember trying
> to get my hatch covers off after building the lip for flush hatches. Even
> after liberal doses of past wax the epoxy was holding on pretty good.

I understand the peel ply is like a microfiber nylon, and it just doesn't bond to the epoxy. You just rrriippp it off.

> 2. I have this vision of the vacuum pressure squeezing out the excess
> epoxy from your layup but where does it go. At best it would come to the
> surface to be sanded down but I don’t think that is right. If it squeezed
> into the peel/ply then I assume you would never be able to “peel” it off

I think the trick is getting the optimum epoxy-to-glass ratio. You completely fill the weave, and the epoxy is "sucked" to the lower surface of the peel ply. I'm not sure if you just keep the epoxy amount down to a level where it doesn't get sucked through, or if the peel ply is dense enough to exclude the epoxy. If you have the right amount of epoxy, you don't need to sand it or anything. (this is assuming you're vacuum bagging the interior of a hull, where the exterior is sprayed against a smooth, polished mold.

> I have never heard of anyone on this board using it so I assume that it is
> either very expensive or provides only marginal strength / weight
> improvements.

I have access to a vacuum pump, but I've never invested in peel ply, breather strips, or hose fittings to try it out.

Look at Ray Jardine's page below. The second 2 boats are vacuum-bagged.

Shawn