I am putting in a new foundation to extend a wall. I have cut away a section of the slab to cast this. The slab is only around 4-6" thick and this is laid on flint which is about 12" thick. There appears to be no DPC bu i guess the moisture can not rise throught the flint. The questions is, how do i damp proof the new foundation. If i lay a DPC layer on top of the foundation near the top of the slab then moister could rise up this and transfer across into the slab. If i lay a dpc at low level then the moisture could transfer across to the brick work laid on the foundation and travel up.
I cant really sand blind the flint becuase there are so many air gaps in the flint the sand would dissapear. Help please.
Also, becuase the flint falls away from under the slab whilst diggin effectively undercutting the slab, once i have cast the foundation, how do i fill the void back up beneatht the slab? Is there an additive i can add to the concrete to make it water proof and hence just fill the hole up killing all birds with one stone.
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I cant really sand blind the flint becuase there are so many air gaps in the flint the sand would dissapear. Help please.
Also, becuase the flint falls away from under the slab whilst diggin effectively undercutting the slab, once i have cast the foundation, how do i fill the void back up beneatht the slab? Is there an additive i can add to the concrete to make it water proof and hence just fill the hole up killing all birds with one stone.
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