19 hours ago, saveasteading said:

I like it a lot. Bricklayers cannot drop mortar down the gap (making a dampness bridge at the bottom) , or their empty cans or fag packets. Plus they can't leave gaps anywhere it is awkward for them.

I've specified it many times and observed it in use. It has been good on site and in life.

Do make sure you have the right waterproof product obviously, as they can look similar, or a bricky might get the wrong stuff.

Ahem, I shall be the brickie - I have studiously watched others throwing bricks on top of other bricks so what could go wrong?? I mean, how difficult can it be???

1 hour ago, stephanh said:

how difficult can it be?

Very difficult for some.

If I declared myself a bricklayer then I would certainly drop mortar down the cavity through incompetence. I wouldn't  "not care", or deliberately chuck rubbish in but some would.

I can't remember how I know how bad it can be....must have had a late need for an extra door or some such.

Plus sometimes could see mortar on a cavity tie. 

My view is that such workers will still be around come the next job, so idiot-proof where possible.

I've seen a coke can below the mesh, with concrete expected soon, and the workers, including their boss,  standing waiting.

I got a very funny look on asking for it to be removed. With their eyes they argued who would have to do it....the culprit or the boy.

Logically there are hundreds of cans in concrete.

Assume incompetence and check often.

Mortar is sloppy work by nature. 

 

If you want zero drips use a different method. Like @saveasteading says the most important thing is a workable system . 

 

My preference had I to do it again would be to extend the cavity as low as possible so that any fallen mortar would still be far below the floor level. 

 

Have a hose on site to give a quick rinse of the ties at the end of every block laying session to clear them of any mortar.

 

Pump the cavity with EPS beads.