[Frankie's Girl]

I haven't used sand. I use mortar mix (like the concrete stuff)

I vary the amount depending on the prop I'm working on, but I've had great success with it. I usually keep it about 3 parts paint/1 part mortar mix, (it's not exact) but adding too much gives you a thicker sludgey texture that makes it hard to apply.

I've been working through a small bag of the mix for YEARS, and it only cost me $5.

It sets up the surface of the prop REALLY well. I've used it on tombstones, cemetery columns made out of cardboard (still going strong after 3 years), my crypt and some small angels and the like. I kind of figure the paint/mix sets up a thin concrete protective coating over everything, and adds great texture as well.

 

[Frankie's Girl]

An example on a foam obelisk I built last year (this was with a brush application):

As long as you're not applying 20 coats of the paint/mix, you shouldn't be able to tell weight-wise that you've got the mix in there.

I used it on my crypt, one coat of the paint with the mortar mix in it, and it really just goes on like normal paint. I have used both roller and brush, and the roller is easier since you get brush marks and have to do some re-brushing or cross hatching as you're painting in order to not get obvious trails in the mixture.

It works both as texture and as a sealant - any latex would be a sealant, but the mortar seemed to add a better seam coverage in addition to the texture. You've got limits on how much to add before it becomes goop, and I always used an airtight container to store any excess (it will pull all the moisture out of the paint and turn into a giant block of gray stuff if you don't)

If you've got some mortar mix sitting around, give it a try on some scrap foam and see if you like how it looks. Couldn't hurt, and at worse you'll just have to get the sand...