A couple of questions.
In theory it is a weakness but this is not usually a concern. You will find pictures of very long walls without movement joints that have moved on the dpc over time due to thermal expansion. A dpc would also introduce a weakness into a freestanding (e.g. boundary) wall.
Not usually. You might if it is a garden wall and you really need a dpc
Usually still 10mm with modern dpcs
It may make a theoretical weakness, but not so in practice. The weight of the wall above gives a good enough bond through friction.
Relying solely on bricks and mortar is not recommended as any slight movement with crack the joints and the DPC will be useless
The DPC felt should be bedded on 10mm of mortar - smoothed flat with no voids, and the next couse of bricks/block laid on a normal 10mm joint.
Felt DPCs under copings and parapets may be more problematic, as there is not much weight on them and so the section of wall above is more prone to movement
dg
Yes.
Your choice. Plastic is chheepp
Uusally almost double. Is that really an issue?
I would agree with dc. The bco cam round to inspect my D.P.C and the two main criteria were that it be bedded on mortar an most importantly that it was @made into the existing D.P.C of the building. What they were looking for wa that the D.P.VC wasn't bridged. In other words you have to maintain the new with the old. Basically taking your D.P C plastic into the existing D.P.C.(Which might be slate)/ In simple terms You have to join the old D.P.C membrane or level with the new one. Whether that involve shoving palstic D.P.C into athe old motar joints at the old D.P.C.
The Natural Philos>
That sounds like the joint could be 20mm, i.e. 10mm mortar, DPC, then
10mm mortar, then brick. Or are you saying the top brick goes straight onto the DPC ? Simon.
I've yet to see a DPC in a mortar bed that's any thicker than elsewhere in a wall. Just look around you at the buildings and you can see for yourself. If you use plastic DPC than the thickness of the plastic is negligible and I have sandwiched mine within the motar bed so there's mortar above and below.
Paul
Yes. The DPC joint is 20mm total and it should be 'weather struck' pointed to distinguish it as a DPC.
dg
The idea is that the DPC is laid on a smooth 10mm bed so that any settlement will not cause the felt to stress or puncture on a void beneath it.
If the bed is too thin then the mortar could crack and felt could be exposed to the frog of the brick or any slightly protruding arris.
It is very common to see only a 10mm DPC joint, but that does not make it correct. Its just laziness of the bricklayer who has just typically rolled out the felt directly onto the bricks.
dg
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