This is classic stuff, the damp old Victorian house that goes from bad
to worse despite all the efforts of dampproofing 'specialists'. And the
cause? The fact that all the wrong things are being done. This scenario
plays out over and over again, so often its a well known deal.
Add to this the twin facts that
a) you dont understand how damp is managed in Vic properties, and
b) you've made mistakes in your conlcusions,
and you cant get to the bottom of it either.
First, if you want to understand damp and Vic properties, I'd recommend
a good long chat at
Now, whats going on:
1. Vic houses handled damp fine when they wre built, they were not pits
of damp. So the basic design is good.
2. Since its damp now, it is what has been changed that has caused it.
What has changed?
1. Airtight double glazing stops ventilation
2. Chimney blocked off
3. Maybe draught proofing elsewhere too
4. Gysum plaster and emulsion
5. Cement render and paint
6. shower installed
All of these increase the damp levels in the walls, and some properties
then begin to fail to deal satisfactorily with the damp.
Contrary to your conclusions, the cause is indeed condensation. Why did
the dehumidifier not cure it? Primarily because it has been going on
for so long that the walls have become soaked, so that it will take
many months to dry them out. Also there are other works that will need
doing to fix it properly, eg the exterior render will be an ongoing
What else needs doing?
The first thing to understand is you need to allow the wall to dry out,
not trap all that water in it, which is what all your presently
considered works are about.
No to tanking
No to rendering
No to painting with water resistant paints
No to a 3rd DPC (!!) (slate should last much longer than 130 years)
Lowering ground levels if theyre at or above the dpc
Checking the drain channel drains properly
Repoint all failed mortar with lime - but dont remove anything thats
Removing all exterior render, and finishing by either cleaning the
bricks up, or if theyre too much of a mess, lime render.
Remove interior plaster and replaster with lime, painting with lime
based paints, not emulsion.
Checking ground water drains away from the house, not to the walls.
And I would add ventilation to the house for your own health, though
this is not necessary re damp until such time as you stop using the
Pay attention to major sources of damp within the house:
Install dehumidifier in bathroom, or maybe a fan.
And possibly enclose the shower so it doesnt produce as much steam in
the room, if practical.
And preferably install a cooker hood
Understand some basic concepts with these houses:
1. More damp is produced inside by breathing, cooking and showering
than comes from outside
2. Thus what is wanted is porosity, to allow the damp out, quite the
opposite of sealing.
3. Damp proofing companies do work so they can get your money.
4. If dealt with appropriately, a Vic house with no dpc, no render, no
waterprofing treatments etc can be dry and healthy.
5. Also be aware that a 9" wall will take a very long time to dry out,
even with the above treatments done.
BTW there is one gotcha: the bricks will be very soft, and the cement
render hard, and it is _very_ easy to do serious brick damage when
removing the render. Proceeed only with serious care on this point.