Rubber Mat Needed for Vacuum Investing

I’m in need of a large rubber mat for vacuum investing, but cannot find one.

About 12 years ago I built my own vacuum machine using a large Rio Grande side-draw bell jar for vacuuming the investment and a stainless steel pitcher for the investment chamber. It worked well.

I lost interest in casting and haven’t used the equipment in many years, but want to resume casting now.

My rubber investing mat (24 inches square I believe) has apparently gone into hiding and I need a new one. Rio still sells the 18" side draw bell jar but the pads they sell have slits in them for bottom draw. I used the 18" jar and a large rubber investment mixing bowl to deal with large flasks and so investment didn’t get spattered all over the inside of the bell jar.

I have tried looking for a large mat (24" x 24") on Rio, Stuller, Otto Frei, Romanoff, Gesswein, Contenti, Cookson Gold and Fisher (Germany) with no luck. I tried using a rubber gym mat, got this after only 1 inch of mercury:


29 inches would have shredded it.

I’m open to using a mat designed for other purposes, but can’t find anything with a smooth side and that is rigid enough to withstand the suction over that large an area.

Surely if 18" side draw bell jars are made, there must be a pad that will work with one. Any help appreciated!

Neil A

(An explanation as to why the slit in a bottom draw pad doesn’t also let air in would also be appreciated.)

You can get any size you need from It is natural gum rubber.

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