damp course under coping stones

[Robbox]

Coping stones over solid wall and no DPC under the stones, rain eventually soaks through coping and makes wall damp.

Would a silicone injection cream placed just under the coping stones do a similar job as a layer of DPM?

Lifting stones to place DPM and probably breaking a few, would be costly in time and materials....would have to source similar weathered coping.

 

[jeds]

I'd treat the copings with a water repellent first. And of course make sure the joints are good. Personally I'd always seal joints with a good polysulphide sealant rather than mortar.

 

[Robbox]

Water repellant done, will look at poly-sulphide for the joints, but we re-pointed all the dodgy ones.

 

[Robbox]

I should have added that the wall is a cavity construction from about 2001. It is block on the inner skin, cavity fill insulation, local stone outer skin with block backing in lightweight blocks.
When we did a small investigation last week, took a stone out, we found that the lightweight backing block was damp. It was quite clear that the lightweight block was damp and the mortar, around the stone we took out, was dry.
So I am trying to work out, is this actually rain penetration through the stone outer skin or is it rain penetration through the coping stones and down through the lightweight block skin?
I know the lightweight blocks are like a sponge, so any moisture ingress spreads rapidly.
I'd love to cure this as it makes a mess of the plastering, especially around the window reveals.