Ian White wrote:
Mathew Newton wrote:

At the risk of entering the 'most obvious question of the year'
competition within the final 10 days I have a question regarding the
likely cause of damp and, more importantly, the best way to 'cure'
it...

My Victorian (1905) terrace has a double skinned (not sure if it's got
a cavity as such, were they built like this?) rear wall that is
rendered and has a Tyrolean top coat.

We have recently noticed signs of damp inside a dining room cupboard,
mounted on the rear wall, and initially put this down to the low
temperature inside the cupboard (~12-14C) due to the rear wall
position. However, it then dawned on me that temperature alone is
presumably not sufficient to cause damp, water is required for this,
and so given that the kitchen/dining room is well ventilated (okay, the
cupboard isn't) and there are no signs of damp anywhere else in the
room/house then it must be coming in from outside.

Looking at the back wall there are no obvious signs of a way in for the
water, no cracks and no dodgy gutters/downpipes. However, knocking on
the render around the area of the cupboard sounds hollow.

Thus, my competition entry question is: Does that fact that the render
has blown mean this is likely to be the cause of water ingress and,
ultimately, the cause of the damp? If so, how does this happen?
Presumably there may well be hairline cracks that I can't see and the
blown render traps a layer of water against the bricks which eventually
seeps through to the inside?

If my assumptions are correct, what is the best remedial action, both
short and long term (i.e. before/after Christmas!)? Replacement will
presumably be the long term fix - it's a small enough area that I'm
more than happy to do it myself - but what with? Would it be worthwhile
removing the blown render in the short term, or will the bare bricks
then suffer just as badly? Should the bricks, before rendering, be
'treated' with anything? Does the render on these old houses serve to
'waterproof' the wall, or is it largely decorative?


Depends where you are. Up here on a hilltop in Scotland, there's
absolutely no doubt!

May I add a related question?

Rusting and swelling of old iron downpipe fixing spikes is a known cause
of cracked render, and our house is a perfect example. But when removing
these spikes, they tend to snap off in the bottoms of the holes. Is it
OK to fill over the deeply buried bits... or is that storing up trouble
for later?

In other words, does it need a simple filling or the full root canal?




Water borne rust particles will permeate water based coatings, but not
oil based. I don't know that they do any real harm though.