Required sub-base for Porcelain tiled patio

5 Nov 2009
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United Kingdom
My current patio is block paved (laid about 20 years ago) but I am looking to have a porcelain tiled patio. My house is on clay soil and I have two large oak trees in my neighbouring garden. I find that during the summer, a gap opens up between the paving blocks and also some of the paving blocks sink due to effectively ground movement beneath the paving blocks caused by clay shrinkage.

Can anyone advise how the sub-base should be best constructed so that I get minimal movement once the porcelain tiles are laid. I am concerned that if the sub-base is not properly constructed, the porcelain tiles will move/crack over time. The overall size of the patio will be 70 sq metres.

I did speak to one structural engineer recently who suggested the following sub-base:
  1. remove existing paving blocks/bricks and excavate soil to required depth
  2. lay sand
  3. lay concrete slab, minimum 75mm deep
  4. lay DITRA Mat above concrete slab
  5. lay poreclain tiles with flexible adhesive
Does what this structural egineer suggest an over-kill? Is there an alternative option?
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