I'm building a shed / outbuilding on some ground that is prone to water logging. I already have several concrete pads on top of which some aggregate concrete blocks will be placed to raise the ring beam off of of the ground.

My question is what sort of mortar mix should I use that has suitable strength use with foundation block work and that will be resistant to water and frost after the soil is replaced around the blocks?

I have established that the blocks should have a compressive strength of at least 7.3N/mm²

Is a simple Portland Cement / Sand mix in a 1:4 ratio as suggested in the bottom row of the table below sufficient?

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Images / plans for context:

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1 Answer 1


Gathered the answer elsewhere. For anyone else searching the same, my architect confirmed 1:1/2:4 CEMENT: LIME: SAND MIX (CLASS M6) for below the damp proof course.

This is confirmed in this table.


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