Chemical DPC above or below existing DPC...

[paulbandler]

"You are also saturating original bricks with silicone"

Well, the mortar between the bricks - this cream stuff goes in the mortar bed.

...so why not find out if your wall is actually wet before you throw chemical into it

The brick courses below the existing DPC are certainly wet - but that's normal is it not? I was thinking that injecting a chemical DPC in the mortar bed one below the existing DPC would supplement the existing DPC in case it was breaking down now or in future.

I've been on my hands and kness today cleaning back some of the brickwork revealed by my earlier work to remove the cement plinth that was bridging the DPC. In some areas the existing DPC is nice and clearly visible in-tact black line along the mortar bed face and kinda gives me some confidence that it is effective and moisture can not get past. In other areas the mortar has come away along with crumbling bits of DPC and I worry that when repointed a natural bridge will be created for moisture to cross. It's for areas like this (and possibly others out of sight?) that I thought a supplemental chemical DPC might have merit...?

 

[Penners]

I was thinking that injecting a chemical DPC in the mortar bed one below the existing DPC would supplement the existing DPC in case it was breaking down now or in future.

Actually you have a point - the dpc might break down at some time in the future. What's more, your roof will possibly leak sometime in the next 100 years or so, so why not pop another one on above it?

OK - I'm teasing, Paul. But I really do wonder whether you're worrying too much about your dpc. Having removed the bridging render, why not give the building a chance to show you whether it's still got problems or not? Drying out can take months.