Introduction: Concrete Brick Casting

My partner wanted something for edging the flower beds and footpaths in our garden. Last summer she edged some of the paths with red bricks. Unfortunately, some of the bricks started to disintegrate over the winter. It was a shame as she had put so much effort into it. So I decided to do something about it.

There were several options: sort through the bricks and find the ones that would (maybe) be a bit more durable, buy something suitable at the DIY store, or make something myself. I chose the latter.

In the end the casting process is probably more expensive than buying something, but all the materials for building the form are recycled, the concrete bricks have a more natural look, and that, surely, is what it is all about.............

Another advantage is that you can cast concrete bricks in exactly the size you need. I wanted something about the size of a brick - 300x150mm, but a little thicker - 100mm - to give them more stability as we are laying them in a soil/clay bed.

WARNING! This Instructable is rather long-winded - but will suit those who need detailed instructions. On the other hand there are lots of images (and a rough sketch at step 3), which will suit those who are more imaginitive and are capable of improvising.

Step 1: What You Will Need

  • A wooden board for the base of the form. Dimensions will vary according to what you want to cast. In my case, a good old-fashioned 20mm plywood 1000x600mm cupboard door.
  • 2 lengths of roofing lath - 700x40x50mm
  • A couple of offcuts of 0,55mm thick galvanized metal sheeting to cover the upper surface of the board.
  • 4 strips of 0,55mm thick galvanized metal sheeting - about 800x100mm each - to contain the long sides of the bricks.
  • 8 wooden blocks - 100x150mm, about 40mm thick - to contain the short sides of the bricks.
  • 3 offcuts of 100x100mm wooden beam, each about 200mm long.
  • 1 length of 100x100mm wooden beam, about 1000mm long.
  • 3 wooden planks about 1000x100x15mm each.
  • Small flat-headed nails about 12mm long.
  • 10-20 20x3mm woodscrews.
  • One long woodworking clamp.
  • Plus basic tools: hammer, screwdriver, drill, tin-snips and saw.

Step 2: The Base

  • First, nail two laths widthways to the underside of the base - about 200mm in from the shorter edges. This makes it easier to manipulate the form.
  • Next, nail the three short lengths of 100x100mm beam along one long upper side of the form. These will form the brace against which you will clamp the sections of the form.
  • The last step for the base is to protect the top surface with the offcuts of 0,55mm galvanized sheet metal. You can use a whole sheet if you have no offcuts, of course.

Step 3: The Partitions

  • Now we need to make the partitions which define the shape of the brick.
  • Take the 100mm wide strips of galvanized sheet and cut them according to the required length of your brick - in my case 300mm - and add 10mm either end which you then bend at right angles to form an upstand to accept the dividing blocks.
  • In the next step you nail these metal pieces along the length of the100mm wide plank as in fig. 2. I have 1 long block and 2 short blocks, which means 1 long and 2 shorts metal pieces with 2 spaces between them for the dividing blocks - 1 between the long and the short metal pieces, and 1 between the short and short pieces. These spaces must accommodate the thickness of the dividing blocks + 1mm either side for a sliding fit

    - in my case this was 42mm. On either end of the plank a short wooden block 42mm from the end of the metal upstands fulfills the same function.

  • You do this on one side of two of the planks, and on both sides of the 3rd (middle) plank.

Step 4: Putting It All Together

  • To put it all together: take one of the planks with the galvanized metal only on one side and stand it up against the 3 retaining blocks on the base.
  • Slot 4 of the spacer blocks into the gaps between the metal upstands.
  • Fit the gaps in the middle plank onto the ends of the spacer blocks connected to the first plank.
  • Fit the last plank, with the galvanized metal on one side only onto the spacer blocks connected to the middle plank.
  • And finally, lay the 1000mm, 100x100mm piece of beam lengthwise against the last plank, and clamp it in place with a long woodworking clamp.
  • In the last image you can see 3 small blocks which are screwed to the base and help keep each plank aligned, thus ensuring the sides of the blocks are right angles.

Step 5: Casting

  • Place the form in a stable position where: you can get at it easily, it can stand for at least 48 hours, and where a little bit of water runoff will not spoil the living room carpet............
  • Take a little oil - anything will do, the thicker the better - and brush all the inside surfaces to enable separation of the form after curing. If you use thicker oil, it is sufficient to do this after every 2nd casting.
  • Now mix your concrete - I use 30kg bags of concrete mixture - according to the instructions on the bag or mix your own - in which case, you know how............
  • Once you get into the swing of things you will find out exactly how much concrete you need for your size of form. My form makes four 150x150x100mm and two 300x150x100mm bricks in one casting, and uses approximately 40 kg of concrete mixture.
  • Fill each section with a trowel, packing it in to the corners and tamping it down.
  • Scrape the excess concrete off the top by running the edge of the trowel along the top edges of the planks and leave to cure for 12 hours before the next step. Cover the form with a piece of sacking or geotextile, etc. to slow down evaporation and prevent cracking.

Step 6: Finishing

  • After the aforementioned 12 hours, keep the form clamped and take a small block of wood and rub the surface of the still softish concrete to give it a more natural rough look - do this gently.
  • After another 12 hours you can loosen the clamp and carefully prise the form apart.
  • Rub the block of wood along the top edges of the blocks to round them off. Handle the blocks carefully still, but the thicker they are the less fragile they will be.

Step 7: Uses, Issues, Etc.

  • You can use your bricks/blocks to build retaining walls, garden borders, paths, etc. as documented by images of my partner´s labours in our garden.
  • To date, I have undertaken about 20 castings using this form and the only issue I have had so far is that one or two of the small nails holding the metal pieces onto the planks have worked loose - maybe woodscrews would be more durable.
  • As mentioned before, you probably do not save any money in comparison with store-bought stuff, but you get that warm feeling of making something with your own hands ............
  • Storage of the complete form is easy as it packs up relatively flat, taking up minimum space in your shed.
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