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Chez Larsson

Making a home in Stockholm, one drawer at a time

Concrete challenge 4, casting a house number

The milk carton project glimpsed in last week's photographs.

This needed a mould that does not exist, so I made one, and the coated card of a milk carton turned out to be exactly the right material.

Choosing the numeral

I looked at a lot of sevens before settling on a heavy sans one, then printed it at the size I wanted and cut it out of the paper.

The mould

Cut the milk carton into long strips. The width of the strips sets how deep the finished piece will be. That is the only measurement that matters here.

The base is a sheet of perspex, and it is the reason the whole thing works: I could lay the paper numeral underneath it and still see the outline through it while building the walls on top.

The concrete number 7 standing in a zinc planter with ivy at its base

Tape the strips end to end into one long band with masking tape. Then bend and tape that band along the outline of the numeral showing through the perspex.

Two things learned:

Milk cartons cut into strips ready to be taped into a mould

  • Lots of short pieces of tape, not a few long ones. Short bits let you pull the card round a curve in small increments; a long piece fights you and lifts at the corners.
  • Keep one edge of the strip flat to the perspex the entire way round. Any gap between card and sheet is where the concrete escapes, and it will find every one of them.

Then more masking tape around the outside to brace the whole mould, because once it is full the card wants to bow outwards.

The finished concrete 7 with its supporting stake, lying on the ground

Sealing

The kit included a natural liquid rubber for exactly this: coating moulds made of paper or card that would otherwise go soggy.

I used it to seal the bottom edge of the mould where card meets perspex. Again to stop concrete seeping out under the walls and ruining the outline.

Casting

Mixing and pouring happened in the garage and outside, which is worth doing. Dry concrete powder is very dusty and you do not want it settling over an indoor room.

I pushed a stake down into the base while it was wet, because this one is destined for a planter and will need something to hold it upright.

The paper numeral seen through the perspex sheet with the mould walls taped around it

It went off in the garage alongside the candle holder from Monday and the bookend from yesterday, all three curing together.