How to cast in concrete – beginners lesson

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Concrete is a cheap material, perfect for a beginner. It doesn’t have to be so messy, and can be done at home, with no need for a permanent studio space. AND you can get fantastic results with no prior knowledge of concrete.

First, What do you need:

  • Cement (I use SNOWCRETE, available from WICKES in 25 kg bag for £14.50)
  • Hard sand (I use Kiln dried sand, available from Wickes in 25 kg bag for £5)
  • Plastic Buckets for mixing in
  • Safety Goggles
  • Mask
  • Good quality Plastic gloves (i.e. Marigolds)
  • Plastic sheets to protect floors
  • Plastic bags or bin bags
  • Moulds – anything from recycled pots to soap moulds or old chocolate boxes!
  • Sandpaper
  • Polyfilla

There is also a long list of desirables, things you can purchase as you go along, but not necessary for the beginner! For example:

  • Wax (I use a clear marble wax)
  • Release agent on spray can
  • Spatula
  • Ceramic scraping and shaping tools
  • Sticky back felt
  • Concrete pigments
  • Plastic fibres

Etc etc etc!

The more you experiment, the better you will understand the material. You will know what resources you require to reach the results that you are aiming for.

Concrete is a material suitable for casting objects. It is possible to sculpt in, but harder and not as common.

When you cast objects, the mould is vital. Long before you start mixing up cement, you need to think about your idea and prepare your mould. For your first experiments I suggest to choose a few different ideas. It feels more worthwhile taking out the plastic sheeting and gearing yourself up in goggles then. Prepare the moulds required and just go for it.

Start walking through the super market looking at shapes! So many products are sold in great containers, you just have to look at them with new eyes.

Take a look at Pringle tubes, triangular yoghurts, juice boxes or ketchup!  The negative shape in between two salad bowls, placed on top of each other, can make a beautiful heavy concrete bowl.  Sand can be used in the form of a hole or as a mound. Ice trays or soap moulds can make super cute little shapes. You can dip things into concrete and you can use large leafs as imprints.

There really is no end of possibilities, but you have to plan ahead.

jelly and yoghurt pots email

It can be a little hard to remove your cured concrete from the mould. If you are using pots from your recycling bag, they can be destroyed and that makes it easier. Hard plastic moulds are a little tricky. Some people oil their moulds. Personally I don’t, as that will give your piece a sandy surface. You can buy release agents and silicon spray specially formulated for concrete and casting, or you can use wax.

When you are ready, PREPARE YOUR AREA! Don’t forget to protect your floors with plastic! I even use plastic when I work on the grass. It is easy to drop a little here and there. Don’t forget that you will be a little clumsier than usual dressed in goggles, mask and gloves…

Which brings me to: BE SAFE. It is important to use googles, a mask and plastic gloves. Breathing in the concrete is dangerous and it can burn your skin and damage your eyes.  I always read the manufacturers safety data sheet for further instructions and I advise you to do the same. Be careful as you handle it in both powder and wet form.

mix in bucket email

Mix your concrete. You need to use one part Snowcrete to two parts sand. Start with stirring the two together well before adding the water. Add small quantities of water at a time. It is easy to make concrete to thin. Aim for the consistency of a thick porridge. Try to squeeze a ball, that stays round, but then sinks into goo when you vibrate your hand! That is how I check my mixes.

You will need to strengthen your material with either ballast or metal rods or both, for larger projects (table tops, stools, benches etc.). I suggest that you start experimenting with smaller bits, and work yourself up towards the more complicated projects.

The thick mix will trap air and result in a bubbly look instead of a smooth one (see picture example of two different surfaces.) Too prevent this from happening you need to tap and vibrate the mould meanwhile filling it. You can see the air bubbles as they reach the surface. Keep going for a while after the bubbles have stopped appearing.

airbubbles versus smooth email

Make sure you place the curing object on a flat surface or it might be tilted. It should be wrapped up in plastic. This is so that it cures in its own time, and not due to drying out. Concrete dries harder if it dries slowly. Wrapping the concrete air tight in a bin bag as it cures, will add a few days to the process and therefor increase the quality and strength of your final piece.

It is sensible to water the object. I usually open the package after one day. The concrete feels hard, but it is still curing. Any visible concrete can be sanded easily at this point, which might be useful in case you want to smooth the bottom of an object or scrape of any protruding bumps. You can water the concrete before closing the parcel again. Just pour some water on top of your item. It will drip of, but moisture will remain in the bag.

Re wrap it and wait for another minimum three days before you take it out again.

Removing an object from a mould is the best part of the process. It is so exciting to finally see the result! But it can, as I mentioned earlier, be a little tricky. A water bath can help releasing the object. Sometimes it is enough to insert a knife or similar around the edge, bending slightly. If you are using a disposable mould it might be easier to just rip it open! Thick cardboard containers (i.e. Pringles) can be soaked until they come apart more easily. It was after a few dreadfully stuck items that tested my patience to the brink, that I went out and purchased my first can of spray release agent! Well worth it as well…

Concrete dries out your skin. It can also still be curing even if it is hard to touch. Curing concrete can corrode your skin and cause serious burns.  Therefor you should always wear your plastic gloves as you remove items from moulds, sand them, scrape them or handle them. 

There might be air bubbles or other blemishes. Sometimes you end up with a damaged edge from bending the object out of the mould. Some of these marks can add beauty, and some are unwanted. You can use polyfilla to fill air bubbles, cracks or scratches.

There are ways to paint it. It is an absorbent material, so you can use diluted colours to tint it. There is also the option of using a diluted PVA to seal the surface first, and then paint it with conventional paint. I prefer to wax it for protection, and leaving the natural colour. I like the vintage look. The Snowcrete comes out bright white, and the piece goes a little yellowish with a clear wax.

Good luck!

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