Black Jack bare wall before new rendering?

pedzblue

New Member
I've had a shell built for an extension where the existing wall connecting to the new wall seems to have some damp penetration about 500mm from the ground all along the 7 metre length. One of the builders suggested to hack off the current render (after a portion of the lower render came off) to up to 1 metre from the ground and then Black Jack the bare wall, and then scratch and re-rendering again.

I'm gonna take on the job of hacking this off as I've done stuff like this before, but need to get some advice on the Black Jacking to a bare brick wall which I've never done.

What's the best method for the render to get a good key? Would it be best to throw some sand in to the second Black Jack application or is there an alternative?

TIA
 
Render will stick lovely to blackjack just give a fresh coat of blackjack before you render make sure it's still sticky
 
Sharp sand thrown at the blackjack whilst tacky is how it used to be done. Haven't seen it done in many, many years.
 
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