I have one of those wonderful house that dont have patio/french doors. I'm therefore going to be ripping out a window in my dining room and installing some sliding-folding (concertinaing) doors in the near future. As I will be chopping down the portion of brickwork below the current window cill, it will result in me having about 1.2m of cavity exposed either side. This in itself is not a problem as I was going to stick some Thermabate (or similar) cavity closer in there.

My question is this:

The current window reveal obviously has the brickwork returned to close off the cavity on either cheek as in the 60's insulated cavity closer were not even dreamed of!. So before commencing, would you expect the cavity be closed off by:

a. brickwork fully bonded to both internal and external skins
b. bricks bonded to internal skin with a full height vertical joint where it butts the external skin
c. brick bonded to external skin with a full height vertical joint where it butts the internal skin (unlikely as there are no internal vertical cracks which you would expect)

In b & c above would they have potentially installed a vertical damp membrane/course/barrier/goo-paint to stop moisture penetrating straight through from outer to inner skin?

Finally, I was going to chop out these bricks currently bridging the cavity anyway, allowing me to install a full height (2.1m) cavity closer. Is this advisable, worth doing or to be avoided at all costs?

N.B. I won't be grinding the reveal down, but toothing out and making good. Don't think the missus (or the little one come to think of it) will like a house full of brick dust caused by grinding! ;-)