Art Concrete How-to
1b: Mixes

THIS PAGE is one of several explaining techniques about how to use concrete in small-scale art projects.

Book: Concrete Handbook for Artists: Technical Notes for Small-scale Objects. More information?

Concrete mixes are variable, and specific to certain applications. As a general rule, the larger the final piece the larger the aggregate. (For descriptions of aggregates and additives see the materials page.) These are basic mixes that I have used and developed over time and work well in terms of plasticity, compressive strength, density and finishing characteristics. I have not suggested liquid volumes as they are too variable (depending on moisture content of the sand etc) but the general rule is to use as little as you can get away with.

Always mix the dry ingredients well first. Then slowly add the liquid, stirring with a stick -- don't use soft wood. For small mixes (jewellery scale) I use plastic containers. For larger mixes a bucket, sometimes mixing with a power drill fitted with a paint mixer, at slow speed. For even larger mixes use a wheelbarrow with hoe or shovel. The new plastic barrels with internal fins that can be sealed and rolled on the floor have been recommended. My apologies for mixing metric and teaspoon measurements, but for the record a teaspoon (tsp) is 5 ml and tablespoon (tbsp) is 15 ml

Very Small Scale (jewellery)
1 tbsp stone dust (screened, limestone or marble)
1 tbsp portland cement (grey or white)
half tsp metakaolin
pinch fibres (if using PVA fibres, do not use latex or acrylic, just water)
(optional) 1 tsp metal filings (silver, bronze)
acrylic or latex solution (as little as possible)

Mesh Sculpture (applied in layers, trowelled)
This is a mix suitable for outdoor use.
1.5 litres sand (sharp, brick or mortar sand)
1 litre portland cement
175 ml stone dust (screened)
80 ml metakaolin
1/6 tsp air entrainer
1/2 tsp super plasticizer
1 to 2 tbsp fibres
water (as little as possible)

Cast Sculpture (poured or placed in a form)
Basically the same mix as above, but you can add washed crushed stone, size depending on the size of the casting.
8 to 16 litres crushed stone
8 litres sand
4 litres portland cement
half litre metakaolin
80 ml fibres
1 tsp air entrainer
4 tsp super plasticizer
water (as little as possible)

Smooth Coatings
To rub into cracks or holes, to overcoat as a final smooth layer.
300 ml portland cement
150 ml stone dust (for smooth you can leave this out)
40 ml metakaolin (if no stone dust, increase to 80 ml)
acrylic or latex solution (as little as possible)

Hyper Tufa
Tufa is a natural porous stone. Hyper tufa ia a cement mix made to imitate it. I have no experience with tufa, but here is a summary of several mixes from other web sites:
---1 part portland cement, 1 part sand, 2 parts peat moss, water or acrylic (latex) additive
---also see:
---1 part cement, 1 part peat, 1 part perlite, 1 part fibermesh, one of several mixes at:

Various aggregates are used to make concrete lightweight and easier to carve. One artist sent me this mix:
"For small projects, I use equal amounts of portland and vermiculite. It takes a while to cure, but this usually gives me time to carve designs. Sometimes I use 4:2:2 portland, vermiculite, and rough sand. I sink some metal (hardware cloth, chicken wire, even clothes hangers) into some pieces using the 1:1 formula." Thanks to Linda Lawlor.
Styrofoam beads can also be used, but they should be coated. See B-Lite in the links page. See materials page for other lightweight aggregates.
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Last update: 2016.