Basic Caststone Ratio

[MikeG]

I am looking for a starting point for caststone ratios. My cast stone is crumbly and falls apart.

I'm using white portland cement, swimming pool mix aggregate (quartz) and an acrylic fortifier. I casting small object, but about to be ready to cast a half-size figurative sculpture.

Thank you for any help you can provide this newbie!

[sculptor]

hi Mike:

crumbly?

what ratios are you currently using?
what is the cure time?
what is the temperature during cure?
what is the moisture content of the mix, and mold?
are there any salts in the agregate?
have you tried it without the fortifier?

[Landseer]

Sandmix ala Sakrete;

Portland cement: 1 part
Sand: 2 or 3 parts

Water: only enough to DAMPEN the above, final mixture should be thick enough to pick up with a shovel without having the stuff run off the shovel like diarreah. If the stuff at all pours like plaster it has WAY too much water and that's why it's crumbly and soft.

To give you an idea of the water amount needed;

That Sakrete sand mix 60# bags you buy at the store with the sand already in it says mix 3 QUARTS of water to that entire 60# bag, much more than that and you get the strength of styrofoam with the looks of concrete.
Remove from the mold in 48 hours, wrap in plastic and seal, keep it wet/damp inside the plastic by spraying some in as needed, and keep it in the plastic for SEVEN days to cure.
It is still curing for at least 30 days.


This assumes you are not adding some oddball stuff like super plasticizers, fast cure chemicals etc.

No idea what "swimming pool mix" is, but concrete is made with SAND or sand and gravel, or sand, gravel and rock if you are building a super highway, for sculptures the sand alone is fine.

I use bags of very fine quartz sand normally used for sandblasting

[nep75]

This is our basic mix, but it is for casting and even laying up with, which means it will be more runny. Another thing - it's for GFRC - Glass Fiber Reinforced Concrete/cement. I think the water can be controlled to get desired consistency.

Portland Type 1 Cement 100 pounds
Silica Sand 80 pounds
Forton VF-774 14 pounds (liquid polymer)
Water 24 pounds
AR Chopped Strand 2.5% to 3% by weight of total mix design
Super Plasticizer 2-12 ounces (depends on what casting conditions are)

There is another ingredient that can be added to make it set quicker called Qwix. This is what a lot of industrial manufacturers are doing. I don't know if this would help with what you're doing. Just thought I would throw my two cents in.
~ niki