Making the mould:
Needs list - wooden strips approx 2 to 2.5cm high, wooden sheets at least 1cm thick ( melamine covered chipboard worked best for my purpose), drill with drill bits and screwdriver attachment, screws, trisquare.
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| Melamine board ready to be cut down to size |
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| Fitting the lateral strips |
It all starts off with deciding on the size of flagstone. Cut the wooden sheet slightly larger than the size of the flagstone to allow attachment of the wooden strips on the sides as borders.
E.g. for a 50 cm square flagstone cut the sheet about 55 cm square (better slightly larger). The extra width it to accommodate the width of the lateral strips.
Cut a 50 cm wooden strip and screw down to one edge. Mark out 50 cm from the inside of the strip at 90 degrees to the 1st strip using a trisquare, and attach another wooden strip. I kept the strip in place with F clamps to drill guide holes for the screws. These were drilled through the underside of the wooden sheet into the clamped strips.
This was done all around to create a box with an internal measurement of 50cm square.
All that is left was is to mix up a batch of concrete and pour it into the mould. I used a ratio of 1 cement: 2 sand: 3 gravel. I did not make a runny concrete mixture. It was relatively stiff but fluid enough to fill the corners and edges of the mould. A waterproofing concrete additive was also added to the mix. The mixture was poured in a bit at a time and a wooden block was used to compress it into the corners and sides of the mould. After the mould is full, use a hammer to tap all around the sides and corners of the mould to encourage the concrete to fill all the mould. The exposed concrete surface of the mould was left rough to create a good key for the laying mortar to grip onto.
This is left to set. After 24 hours 2 of the sides of the mould are unscrewed .This is where the drill with screwdriver attachment come in handy. Remember that this process will need to be repeated for every slab made. Your drill will need a reverse switch to undo the screws. A few gentle taps on the mould with a rubber mallet should release the slab. No release agent was used ( a release agent can be applied prior to filling the mould to allow the slab to release easily). I found that used of melamine boards allowed the slab to release without the need of this. It also created a very smooth surface.
The slabs can be left to cure for a few days. If not mistaken there is a 28 day curing time for this concrete, however I started to lay them after 1 week.
Make no mistake even though making the first few may be fun, this is an extremely labour intensive process. Check your square area before you decide if you would like to undertake this.
The laying is done in the same way as the process mentioned for:Re- laying old cement tiles
However keep in mind a 20cm square tile is much lighter that a 50cm square concrete one.
E.g. for a 50 cm square flagstone cut the sheet about 55 cm square (better slightly larger). The extra width it to accommodate the width of the lateral strips.
Cut a 50 cm wooden strip and screw down to one edge. Mark out 50 cm from the inside of the strip at 90 degrees to the 1st strip using a trisquare, and attach another wooden strip. I kept the strip in place with F clamps to drill guide holes for the screws. These were drilled through the underside of the wooden sheet into the clamped strips.
This was done all around to create a box with an internal measurement of 50cm square.
All that is left was is to mix up a batch of concrete and pour it into the mould. I used a ratio of 1 cement: 2 sand: 3 gravel. I did not make a runny concrete mixture. It was relatively stiff but fluid enough to fill the corners and edges of the mould. A waterproofing concrete additive was also added to the mix. The mixture was poured in a bit at a time and a wooden block was used to compress it into the corners and sides of the mould. After the mould is full, use a hammer to tap all around the sides and corners of the mould to encourage the concrete to fill all the mould. The exposed concrete surface of the mould was left rough to create a good key for the laying mortar to grip onto.
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| Exposed surface in mould was left rough. This will be the underside of the flagstone. |
This is left to set. After 24 hours 2 of the sides of the mould are unscrewed .This is where the drill with screwdriver attachment come in handy. Remember that this process will need to be repeated for every slab made. Your drill will need a reverse switch to undo the screws. A few gentle taps on the mould with a rubber mallet should release the slab. No release agent was used ( a release agent can be applied prior to filling the mould to allow the slab to release easily). I found that used of melamine boards allowed the slab to release without the need of this. It also created a very smooth surface.
 |
| The finished product. Slabs with small defects or chips were left for cutting down to size such as close to walls. |
The slabs can be left to cure for a few days. If not mistaken there is a 28 day curing time for this concrete, however I started to lay them after 1 week.
Make no mistake even though making the first few may be fun, this is an extremely labour intensive process. Check your square area before you decide if you would like to undertake this.
The laying is done in the same way as the process mentioned for:Re- laying old cement tiles
However keep in mind a 20cm square tile is much lighter that a 50cm square concrete one.
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