Using casting sand as an sculpting medium

Just bag it and draw the gas through the sand as you would resin in a mold. I found this site has just about everything you need for vacuum bagging. Joe Woodworker - Woodworking, Vacuum Pressing and Veneering Website

 

Hi guys,

Another update. I'm doing tests of 40*40*40cm (I'm getting a concrete mixer soon, because even with a powerful drill this is impossible to do with these quantities), casted in concrete plywood boxes. I'm using 6% concentration at the moment and 1:100 Propyelene Carbonate catalyst, but the block takes too long to dry. I let it set all weekend and the top was nice and dry, but the sides and the inside were still wet. I don't get this, since the silicate dries chemically, not by evaporation. I didn't add any extra water. Does anybody has a theory for this?

I'm waiting for my vacuum bags to arrive. I'll let you know how that goes!

Best regards, thanks again

 

It cures on exposure to CO2 and not enough CO2 is making it to the sides or interior so they remain wet.

 

Drill some gas holes in the plywood sides and bottom to let the CO2 enter at different places. You could even tape a garbage bag over the top of the box so you can visibly see how much gas has passed through the sand. Ideally you want to inflate the bag to the same volume as the sand in the box. Leave it sit for a while with the bag to seal the CO2 in.

 

Hi Rocco, even if I'm using the catalyst? I'm using 1:100 Propylene Carbonate to Sodium Silicate. If it cures on exposure to CO2, then what does the catalyst do?

 

Tana, I think you know that the 1:100 suggestion I made was something I had not actually tried. You are right to think that if curing as opposed to drying were occuring, the block should have cured all the way through. So, I would still expect that a reduced ratio of PC to SS should result in reasonable cure times. One way to to try to find that ratio without making large blocks of sand could be to simply use some plastic pipe that is perhaps 50cm long and maybe 25mm diameter and pack several pieces with sand bound with varying ratios of SS to PC. Maybe try 1:20, 1:30, 1:40,1:50. If you pre-drilled a 1/4" hole at the mid point of the pipe and then used aluminum HVAC tape to cover the hole, you could probe the sand at the mid point without destroying your test piece.

The one thing that this pipe-method does not replicate is the potential for the curing sand to produce significant heat which may become more of a factor in a block of sand. But, it at least will let you see whether you can cure the sand at a reduced PC:SS ratio. After that might come a 40X40 cm block with a themometer stuck deeply into it.to see how hot the center is getting. I guess the heat should not have a dleterious effect unless it got up around boiling and maybe even then it would not be harmful. Don't know.

Thanks for the update. I was wondering how things were going.

Incidentally, I have gassed sand mixed with 1:10 PC:SS and it works very well. But even with a cement mixer (rented?) you probably could not get your mixing and packing done in time on a large block.

Denis