Installing a plastic DPC in a Victorian house with brick cavity walls.

[Jake]

I'm interested in curing a dam problem in my Victorian house (brick-built cavity walls).

If left to my own devices with no advice, I'd be inclined to use a large angle grinder to cut through each skin if the wall along a horizontal joint, (say four feet at a time, and slip in a a section of the black plastic damp proof membrane they use in modern houses. The brickwork above the DPC would then of course drop down the remaining

1/8" or so onto the DPC, holding it in place. (I envisage that this tiny bit of subsidence would not cause any serious problem. The house was built with lime mortar, by the way. Unfortunately it was then rendered with cement mortar, right down to ground level.

Thank you for any comments on the above.

Jake

[Dave Plowman (News)]

I've seen this done using a two man hand saw.

[N. Thornton]

Good lord.

NT

[Malc]

I remember talking to one builder who said that he'd saw through a house and feed in a lead DPC. I was somewhat incredulous at first but he insisted it was not an unusual thing to do.

-- Malc

[Capitol]

The BBC showed it being done with a hand saw in the original (Barry Bucknell) diy program 40? years ago and IIRC in a solid brick 9" wall. I'd have thought either a diamond disc in the angle grinder or a jigsaw/reciprocating saw with the appropriate blade set(the slot needs to be wide enough to take the insert) would be fine in lime mortar.

Regards Capitol

[The Natural Philosopher]

Indeed it is not.

[N. Thornton]

I gather physical replacement dpcs are more popular on the continent. However it is a wildly inappropriate solution for a Victorian house that worked perfectly when built, and merely needs some fairly obvious issues sorting out. Sawing that much out can cause a lot of cracking and worse in a house thats not the most stable - as is the case with some Victorians. To saw 4' out and expect no problems is just idiotic.

NT

[Pete C]

Hi,

Before this, run a dehumidifier and if there is a cavity in the wall see if you can ventilate it and what difference that will make, Also make 110% sure there are no leaking pipes or gutters etc. Send away brick sample for analysis to see if it contains salts indicating rising damp.

If it really is rising damp opposed to damp from within the house try cutting a pair of slots in the render with a grinder first to see if it can be chiselled out easily with an SDS drill. If so then cutting away render at the bottom to at least 2x the thickness of the bricks might allow water to evaporate out instead of rising.

Does the house have double glazing or other modern glazing at all?

cheers, Pete.

[Andrew Gabriel]

That can do a lot of damage -- they can all too easily dry things out much too much, resulting in dish shaped floorboards and the like (been there, done that). If you think the humidity is significantly higher inside the house than outside, ventilate it more. Buy a couple of cheap greenhouse humidity guages if necessary so you can compare.

[Dave Plowman (News)]

But they don't remove one course. I'm not exactly sure how it's done, but it's just the thickness of the saw - so just slightly more than that of the membrane. Perhaps someone can give chapter and verse?

[Rob Morley]

He said 4 feet, not 4 inches :-)

[N. Thornton]

so dont set it to too dry a setting.

[Dave Plowman (News)]

Right. Not sure why it would move, then.