artistic concrete paving blocks? Post your questions and get answers regarding all areas of drives, pathways and patios

[artist]

Hi there! I was wandering if someone out there can help me with my art project! I am attempting to make concrete paving blocks in the Hall of fame fashion, basicaly to make concrete paving blocks that would be movable and would have hand imprints of various people as well as lettering or metal plaque inset at the top. These will create a temporary replacement of some pavement slabs, but have to be removed at the end of exhibition. I have huge diy experience, but no experience of working with concrete, so please provide as much info as possible in your reply - basicaly I need to know everything, from how to make it, to where to buy concrete mix, to some idea of cost. Also any helpfull suggestions of alternative materials or ways of creating this would be greatly appreciated. I will give you full credit to being my expert adviser on the project. Many thanks

[thedoctor]

A frame (preferably steel) needs to be made to the dimensions you require. This frame (no base, just sides) sits on a sheet material, again, preferably steel but timber will be ok. The inside of the frame and the base material are coated with a liquid called mould oil which is available from builders merchants. The concrete is mixed using pea shigle (4 parts) sharp sand (2 parts) and cement (1.5 parts) its mixed fairly wet and placed ion the mould. Ideally your base would be a vibrating plate but these are extremely expensive so you need to hire a vibrating poker from a tool hire shop and this need to be dipped into each mould about 5 times and held there for 5 seconds. You will see all of the air bubbbling out of the concrete, as it should, leaving the concrete as dense as possible. The slabs are then left for about 3 days before the frame is lifted off (during which time you will be able to put hands etc in) and then, left for at least 3 weeks before you attepmt to lay them anywhere.

[artist]

Thanks for your reply - very informative but unfortunately as I said I'm a real novice to this concrete business and some things are still unclear to me.
First, the concrete mixture that you are suggesting to me doesn't add up, so am I assuming correctly that 4 parts shigle + 2 parts sand + 1.5 parts cement = 7.5, so the remaining 2.5 part would be water?? Can this sort of mixture be purchased pre mixed, and if so where?

Second, what quantities of these materials do I need if say aproximate dimensions of each slab are 80cm x 80cm? And how thick do slabs need to be in order to be tough enough to be walked on? If they are to be laid on top of existing pavement can they be thiner?

Third, how dangerous are these materials? As I will have other people involved I have to be very careful about health and safety issues. If handprints are taken, does skin need to be protected in any way, and can the mixture wash off easily?

Are there any other things I should be careful about?

Many thanks