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How thick should concrete be to keep it strong, non-brittle?

Also, will concrete stick to strong corrugated cardboard, steel, aluminum, plastic? How can you get concrete to take a particular shape (and dry in that particular shape) without it becoming messy and uneven? 

These questions are for a sculpture project that I am working on.

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Toga_Dan1 month ago

I've sculpted mortar mix over styrofoam. Pretty easy to sculpt the foam with sawsn kitchen knife, rasp, etc.

Toga_Dan1 month ago

Read up on stucco technique. Styrofoam, metal lath, etc.

Toga_Dan1 month ago

Google "slump test ".

Sometimes you can work small with no form. A bit like sand castles. You'll get a feel for it by doing. If u mess up, at least it's cheap.

seandogue1 month ago

Add shredded Fiberglas and latex binder (often recommended wench repairing stair threads and other damaged areas that have thin edges) to the mix for additional strength when used in thin layers.

Do not use traditional "concrete" for thin layers. Use mortar or sand mix instead.

If this is in prep for casting, you might consider something more like plaster of paris or base layer material for plastering a wall (similar to concrete and hard as nails...very fast cure) (a 'plastered wall' has three components, lathe, which is nailed to the wall studs, to which a layer of base material is added (shallower than the final wall thickness), to which the final layer of plaster is applied after the base has cured.)

To keep such a thin layer smooth, keep it damp at all times, and smooth using a trowel or spatula, or even your hands if you're a sculptor to "float" the material. Be warned, the stuff sucks moisture out of the skin.

rickharris1 month ago

The majority of concrete statues etc you see are made in rubber moulds.

Getting it to stick on non-horizontal surfaces is a problem.

If you can put lots of pins or small nails in your vertical surface it may hold better.

render is about 1 mm thick but is on a brick under surface which gives it strength.

Metal and cardboard can be troublesome.

Cardboard and paper will break down because of the moisture.

Wood and metal need to be coated with a mold releasing agent.

Plastic molds and concrete; depending on the shape of the mold, the concrete pops right out.