Extending Concrete Slab – Best Methods and Practices

concrete

I have a 10 x 10 slab (4 inches thick) that is already in my back yard in the corner. I bought a kit to build a 10 x 10 shed on it, and then realized that would put it right up to my fence. So my thought is to essentially extend the size of the slab to a 11 x 11. This should give me enough space around it.

Since I have not really tried to attach new concrete to existing concrete before, what is the best method for this. Two of the four walls of the shed will be resting on the new portion of concrete I pour, so I want to make sure they do not pull apart over time.

Any suggestions?

Best Answer

Your best bet for a good finish relies on doing three things:

  • Making sure that the foundation for the extension is well compacted and onto good material
  • Cut back and scable the joint with the existing 10x10 slab so that there is a good bond when the new concrete is cast.
  • Drill and fix dowel bars into the existing slab across the joint with the extension.

The number and type of bars will vary depending on the load from the new shed but you should be fine with something like 8mm (3/8") bars at 200mm (8") centres.

You should probably note that this will give you a full structural connection and so may be too much for your particular problem unless you want to be absolutely sure that the slab and the extension don't separate.

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