Exterior insulation of cavity wall

stuart45

Chickereeeee said:

stuart45 said:

A solid wall built in Stretcher bond will still have wall ties. It looks like a cavity wall from the outside because it's built with stretchers. It's the same when you build a 9inch garden wall in Stretcher bond, you use ties. 
The cavity here can only be 10mm because the wall needs to be the correct thickness for a brick on edge finish. With a house wall it could be increased to about 20mm to make the laying of the inside stretchers easier.
Bricklayers used to call it a finger cavity, because it was just enough room to get your fingers down when laying the bricks.
Although most solid walls were built in Flemish bond, stretcher bond was a bit cheaper as it used.less face bricks.
Normally CWI companies won't fill a narrow cavity.

OK, I (obviously) don't know ow much about brick laying.

What bond is a normal cavity wall, then?

 I an not sure what you mean by 'correct thickness for a brick on edge finish'. I assume this is the final layer along the top of a garde wall? If so, I don't think there is such a restriction here (top is open) but they would use the same approach?

A normal cavity wall is stretcher bond. 
 A garden wall built in Stretcher bond has a 10mm cavity. Building the other side of a wall with a 10mm cavity takes the skin off the back of your fingers, but sometimes it's the only way.
Increasing the gap when possible makes life a lot easier. With a house wall the cavity of 10mm can be increased as the inner brickwork is plastered and the top isn't seen.
Having knocked out for a door in a wall like that you can see the gap was half full of mortar where it has dropped down and stuck.

Chickereeeee

The wall is about 12 inches thick, including render on the outside and plaster on the inside.

Bendy_House

Would pouring poly beads down from the top have any success, do you think? Do these small cavities tend to be continuous?

stuart45

It might be a proper cavity wall then. Depends on the brick sizes, and thickness of plaster and render. Companies will usually drill in a number of places to check the size of the cavity.

Chickereeeee

stuart45 said:

It might be a proper cavity wall then. Depends on the brick sizes, and thickness of plaster and render. Companies will usually drill in a number of places to check the size of the cavity.

4.5 inch brick width.

Chickereeeee

stuart45 said:

pproach?

A normal cavity wall is stretcher bond. 
 A garden wall built in Stretcher bond has a 10mm cavity. Building the other side of a wall with a 10mm cavity takes the skin off the back of your fingers, but sometimes it's the only way.
Increasing the gap when possible makes life a lot easier. With a house wall the cavity of 10mm can be increased as the inner brickwork is plastered and the top isn't seen.
Having knocked out for a door in a wall like that you can see the gap was half full of mortar where it has dropped down and stuck.

Thanks, I understand.
I had  some French doors replaced, which exposed the cavity, and it looked pretty clear of mortar, down to the bottom. 

stuart45

Bendy_House said:

Would pouring poly beads down from the top have any success, do you think? Do these small cavities tend to be continuous?

The really small cavities are usually half filled as they weren't really built with the intention of being a proper cavity wall. A cavity wall back then was a 2-3 inch cavity. Not sure about pouring beads in from the top.
Rule of thumb for cavity size is that is needs to be wide enough to drop a crushed up beer can down and not get stuck in sight.

stuart45

stuart45 said:

It might be a proper cavity wall then. Depends on the brick sizes, and thickness of plaster and render. Companies will usually drill in a number of places to check the size of the cavity.

4.5 is quite wide for a brick, they are normally around 4 1/8 to 4 1/4.
Hard to say if it is a proper cavity wall.