Why do the sell 112mm dpc?

[davidmiller]

Anyone know why you can buy 100mm dpc and 112mm?

 

[cdbe]

Old bricks were wider.

 

[stuart45]

It's because NHBC guidance is that the horizontal DPC just above ground level projects 5mm each side of the face brickwork. As metric bricks are 102.5mm, and the DPC is 112.5mm it gives you that. I don't think anyone takes any notice of that.

 

[berty3000]

I've heard it said, when repointing, that it doesn't matter if you lose some of the DPC edge and can just fill with mortar. I've heard 15mm or so doesn't matter. I don't quite understand why as it would seem to allow moisture around the DPC. But if true, it presumably then doesn't matter if the whole brick course is covered anyway at the DPC level?

 

[stuart45]

I've heard it said, when repointing, that it doesn't matter if you lose some of the DPC edge and can just fill with mortar. I've heard 15mm or so doesn't matter. I don't quite understand why as it would seem to allow moisture around the DPC. But if true, it presumably then doesn't matter if the whole brick course is covered anyway at the DPC level?

All sorts of things get said about rising damp, but most of it is wrong. Damp will find it's way through some really small areas, so 15mm would be no problem.
Back in the 70's, it was common practice to cut the DPM off flush with the slab, and not lap it into the DPC. Although only a small gap, it was found to sometimes allow moisture up into the plaster above and cause damp patches over the skirting boards. BRE started recommending 3 coats of Synthaprufe at the join.
Having said that, if it was on a cavity wall, a small amount of damp wouldn't be so much of an issue on the external skin.

 

[Notch7]

All sorts of things get said about rising damp, but most of it is wrong. Damp will find it's way through some really small areas, so 15mm would be no problem.
Back in the 70's, it was common practice to cut the DPM off flush with the slab, and not lap it into the DPC. Although only a small gap, it was found to sometimes allow moisture up into the plaster above and cause damp patches over the skirting boards. BRE started recommending 3 coats of Synthaprufe at the join.
Having said that, if it was on a cavity wall, a small amount of damp wouldn't be so much of an issue on the external skin.

I always think lapping the DPM into the DPC introduces a slip course as the DPM is completely smooth and the mortar will not stick to it -but I guess the argument is with a cavity wall the internal skin is connected by brick ties to the outside skin which should be solid at the DPC as that is ribbed so should grip

 

[berty3000]

All sorts of things get said about rising damp, but most of it is wrong. Damp will find it's way through some really small areas, so 15mm would be no problem.
Back in the 70's, it was common practice to cut the DPM off flush with the slab, and not lap it into the DPC. Although only a small gap, it was found to sometimes allow moisture up into the plaster above and cause damp patches over the skirting boards. BRE started recommending 3 coats of Synthaprufe at the join.
Having said that, if it was on a cavity wall, a small amount of damp wouldn't be so much of an issue on the external skin.

That would explain why the floors in my 1960s house and in the 70s extension all have a narrow trench separating the slab from the walls. In the 1960s part of the house, the floors got a surface "DPM" (tiles) that couldn't really be connected to the DPC in the wall, and in the 1970s part where they did use visquine, they were perhaps still in older habits or hadn't figured out that connecting it to the DPC would be a good idea?