Is it normal for Rubber cement paint to stiffen up latex castings a bit?

I'm using rcp [ bestine rcp thinner and best test white rubber cement. 
I'm doing a ratio of 1 parts rubber cement to 3 parts thinner.

I have noticed it seems to stiffen up the latex a bit .Normally I'd lay a casting down on a flat surface and it flattens but when it's painted it stays a bit more rigid.

Is this normal?
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