ARTWORK PROGRESS: sculpting with concrete

Rationale
This post covers the process of applying rapid set concrete to the wire mesh and armature. Rapid set concrete hardens in 20mins and cures in 48hours. Making the process of working with it easier and faster but at the same time requiring you to commit to completing the artwork in one session.

Preperation 
Materials required
5 bags of rapid set concrete ( sand and cement mix without gravel, essentially a mortar mix)
trowel
large paint tray for mixing
bucket of water
measuring cup ( for water to concrete ratio)
concreting gloves
dust mask (due to toxicity of rapid set concrete)
large coarse hair paint brush


Step 1: Position the sculpture 
Choose a place that will have shade all day, this will increase you work time on the surface of the concrete. This place will also need access to water and be a place where concrete spillage will not be an issue. You will not have time to clean up during the creation of a large work due to the setting time of the concrete. I chose to create the work on a trolley so that I could move the work for installation afterwards.




Step 2: concrete application
This process will have a rough finish and have to be done as quickly as possible. The intention is to get as much of the wire mesh filled and covered in concrete as fast as possible.
The mix ratio of the rapid set concrete is:
1 part water to 8 parts concrete
This mix will create a concrete that is similar to a soft clay consistancy, it can be molded to a shape and not fall. Note that ratios change with humidity, heat etc. You will need to play with a mix first before attempting a large sculpture.
The concrete is then applied to the mesh from the bottom to the top. filling the legs and hips first so that they are solid then working your way up to the head. then down the arms from the shoulders.
You have to apply the concrete itself with a firm, bottom to top, single application. The finish will be very rough. But that is ok. The concrete will have started to set by the time you cover the entire form which means you can begin surfacing almost immediately.





Step 3: Surfacing
Once you have covered the entire form in concrete, the lower portions of the sculpture will have hardened enough to begin texturing. Using a large (15cm) damp/wet coarse hair brush (hog hair) brush the surface of the lower half of the sculpture and work your way up the form. You will find that the concrete will smooth out as you brush. If there are any major inconsistancies in the form you can add more concrete to the surface and brush out.
Once this basic brushing has been done all over the form, go back over the surface with a soft wet brush. Continue this process until the desired surface texture is achieved.




Pictured below is the method for doing the undercuts of the arm, paper/plastic molds were used.



Step 4: Curing
As soon as the surface has been textured the whole figure needs to be wrapped in plastic for overnight storage. The sculpture cannot be moved or touched for a mimimum of 12 hours. Leave overnight.
The following day unwrap the sculpture, it will still be 'green' (wet). The curing process during the next 12 hours will need to be monitored. Once the concrete begins to dry out it will need to be gently wet down with water once. This will prevent uneven drying and possible cracking. The sculpture will then need to cure over the next 2 days before it can be moved.