Depends on the size of the repair, for smaller stuff, I tend to just use plastic taped as tightly over it as I can, then a layer of mattress foam with a heavy weight on top.
I have my vacuum set about 1/4 to 1/3 atmosphere, (or "fair" on my ancient automotive vacuum gauge)

Thanks, knowing this will make the repair easier. Just need to make sure I'm careful with the amount of resin and use that squeegee to my advantage.

Awesome - so I can do it either way!

It made sense to me if you have a vac pump then why not use it, it is how the board is made in the first place.
For small repairs and glassing on top of the D-cell it will be a toss up for the extra cost and hassle of using the pump VS the few grams of weight saving on the final laminate.....but I get it now that with good technique either way will result in a repair that will last.

I converted some of units of measurement for reference:

0.30 bar = 8.9"Hg
0.45 bar = 13.3"Hg (Maximum)

1/4 atmosphere = 7.5"Hg
1/3 atmosphere = 9.0"Hg

The 'board lady' suggests 7" to 8" Hg for a D-cell repair and its nice for a beginner like me to know that everyone is in that ball park.

srtgumbee said..
Thanks for the tips on breather and peel ply alternatives.
As a beginner I used actual peel ply and breather as I didn't want to second guess my self. On my first practice, I left out using perforated release film (I thought peel ply was water proof - which it is not! ) and way to much resin got drawn out of the laminate.
I used perforated release film on my actual repair and it worked a treat!

Do you have a substitute for perforated release film? use a vacuum bag and punch your own holes in it?

I put the ripstop nylon straight onto the wet laminate, shade cloth on top (as resin absorber), plastic sheet on top, tape it all down, more shade cloth (as breather) then into the vac bag. The nylon does the release film job and peels off the cured laminate.
When buying the ripstop I makes sure I can breath thru it and that it doesn't rip easily. Had some once which tore as I peeled it off which was a pain.

I think they make perforated film for a reason. It is more "flat bits" than holey bits. Shade cloth is the other way around.

Peel ply is not needed unless you are going to laminate over it - all it does it make the resin surface rougher to avoid sanding.

Perf film, followed by a synthetic absorber like thin wadding (6-8mm ish) to pick up the excess bleeding thru the perf film and it also acts as a breather. Seems rather simple to me