At my wit's end with damp!

[Dampnomore]

Hi all,

As the title says really.

I own an ex council semi detached house which was built in 1920, in the 1980s it was modernised internally by the council and since then had work done to it by the previous owner. It seems I have inherited a damp house when purchasing it. I bought during the summer 4 years ago so there were no signs of anything untoward, I didn't really know much about damp back then though to be honest.

The floor is concrete, all the walls throughout the house are brick and is all plastered with gypsum plaster, it is double glazed and has central heating.
Outside, part of the house is rendered with a heavy cast render, I don't know if it is cement or lime based. There are 2 pilasters and a plinth on the front of the house.

The problem I have is that I can't wallpaper anywhere downstairs without the bottom part peeling off. When I originally stripped off the woodchip paper from the whole of downstairs I could see the shape of the brickwork as if the mortar joints were wet, even on the interior walls, some of which had the so called tide lines.

I called a damp surveyor and had a liquid dpc injected through his recommendation which didn't solve the problems, so I called an independent surveyor who said it was just condensation.

I decided to start my own research and try and tackle some work myself which has now opened up a whole new can of worms.

First of all I decided to lower the ground level all the way around the house, then the plinth I mentioned earlier had been rendered over with a cement render and started below the damp proof course up to the top of the plinth, basically bridging the damp proof course. Once I removed this most of the bricks had badly blown and the mortar had turned to dust. The original dpc is made of slate and is now very brittle. One of the pilasters had a loose brick so I took it out and found the cavity to be filled with soil or the dust of the perished mortar, I can't tell which.

I was originally told that the house had no cavity so on 1 of the walls without the pilaster or plinth I took out a brick to check only to find a hell of a lot of expanding foam!

I'm currently confused as to what direction to take now as everything I do to try and find the cause I find more problems.

Any advice would be greatly appreciated.

 

[Feltwell]

It sounds like what you've done so far is sensible. How long is it since you lowered the ground levels and removed the rendering from the plinth? It will take a long time to dry out, I've heard a month per inch of wall thickness quoted.

If the house has cavity walls, you don't need to worry about the render on the top part being breathable - it doesn't need to be. However the render needs to be in reasonable condition and not letting water in through cracks.

Don't worry about a slate DPC being brittle - slate is brittle! It doesn't degrade when buried inside a wall. You've already found that part of the cavity is blocked, that could be your problem, the only way to clear it though is to take bricks out and physically extract the debris. Usually this is done from the inside, although if the outside is going to need to be rendered over again anyway then you may as well do it from there. You can remove a brick and use an endoscope to see inside the cavity (you can get cheap ones now that connect to mobile phones, Lidl of all places was selling them recently!), or a popular quick way is stick your hand in with a phone and take some pictures.

Your "expanding foam" - are you sure it was that, and not cavity wall insulation?

1920 is about on cusp of construction changing from solid wall to cavity, it depends where you are. My first house was a late 1920's ex-Council house in Hampshire, that was cavity, my friend had a late 1930's place in Bristol that was solid walls. The brick pattern should be able to tell you what you've got - or drill a few holes! If you can only see the long faces of the bricks showing on the plinth part you've exposed, chances are it's cavity (Google "stretcher bond"). If you can see the short faces every few rows, it may be solid.

 

[88v8]

Hello and welcome.
Rotten luck.

If the house is sealed up tight as a drum with double glazing and no open chimneys, there may be an element of condensation. Kitchens with no extractor fan, unvented tumble driers, drying washing indoors, all these things are detrimental.

But what you are describing is rising damp. If it's also in the internal walls, that's pretty bad and indicates that the dpc has been bridged or was never properly installed in the first place.

How about your neighbour's house? Is that damp? If not, why not? What's different?

Ivor

 

[paulc]

1920 is about on cusp of construction changing from solid wall to cavity, it depends where you are. My first house was a late 1920's ex-Council house in Hampshire, that was cavity, my friend had a late 1930's place in Bristol that was solid walls.

My semi was constructed around 1928/9, and is a combination of cavity walls on the ground floor and solid brick on the upper. Where to two different types of construction meet, there is a course of corbelled bricks topped with a layer of flat clay tiles - This "feature" is very common in many of the properties built in Norfolk between the wars, although sometimes the course of tiles are omitted.

Generally, the solid brick wall will have been pebbledash rendered and Norfolk Reds (a soft friable brick) used to face the external cavity walls. Wall thicknesses will be around 200mm for the solid construction and 250mm for the cavity walls.

 

[Dampandmore]

Thanks for the replies.

I removed the render around 3 months ago and lowered the ground level 2 months ago. Since then I have noticed the wet looking bricks where the render had been applied has dried out significantly with just the course below the dpc looking wet, I’ve read that this is a good sign.

The house I guess is sealed up tightly with the double glazing and I have sealed up the fireplaces (with the relevant vents).

I’m also guilty with lack of ventilation in the kitchen and bathroom.

The foam looks and feels like expandable foam, it also breaks off in crisp clean pieces. I don’t know what the foam is like in the dpc injection type.

 

[plasticpigeon]

I wonder whether your house originally had a suspended wooden floor, which has since been filled in with concrete. If that is the case, and especially if the concrete is above the damp proof course that could be the cause of the internal damp. Is there any evidence of there ever having been air bricks below floor level? Unfortunately a lot of work done to "modernise" houses often ends up causing problems.

 

[Dampandmore]

I have wondered whether or not the house originally had wooden floors. I have no vents at ground level but my neighbours do. They also have concrete floors and suffer with damp.

 

[Anonymous]

Sorry, I tried not to reply... I really did... no such thing as rising damp. Remove the concrete open some windows, let the air circulate find and reopen the under floor vents, unblock the chimney's etc etc... let the house breath and it'll all go away. aAAAAAGGGGHHH !

 

[Dampnomore]

Thanks for the reply,
The problem with the concrete floor is that I don’t know if it’s original. I have asked the local council and all they could say was the estate was modernised in the 80’s.
I have no vents and no evidence of any vents ever being there. I’m guessing my neighbours at some point had the air vents fitted as a way to stop the damp in the same way our house had a rendered coat on the plinth of the house. I’ve read a lot about damp and the myth of rising damp and do try and keep the air circulating.

 

[Zebra]

I'm not sure but I'm interested to know, how is cavity wall insulation supposed to not breach the dpc? I'm guessing the dpc in modern houses bridges both leaves of the cavity, so the insulation can't fall below it, but is this the same with slate dpcs? Do they span the cavity?

 

[Kearn]

I'm not sure but I'm interested to know, how is cavity wall insulation supposed to not breach the dpc? I'm guessing the dpc in modern houses bridges both leaves of the cavity, so the insulation can't fall below it, but is this the same with slate dpcs? Do they span the cavity?

Surely it's not a complete DPC if there's a gap in it?!? I can't see why slate wouldn't have bridged the gap also, same principle, different material, surely?! My only experience of slate DPC is on solid brick construction...

 

[paulc]

I'm not sure but I'm interested to know, how is cavity wall insulation supposed to not breach the dpc? I'm guessing the dpc in modern houses bridges both leaves of the cavity, so the insulation can't fall below it, but is this the same with slate dpcs? Do they span the cavity?

Having watched a neighbour build an extension last year and some 70 new builds currently being erected in sight of my bedroom window... The DPC does not bridge the cavity and the insulation (rigid batts or PUR foam boards) are held in place with the wall ties.

If you think about it, a continuous DPC across the void would allow moisture to track across to the inner leaf, so a gap is required.

 

[Dampnomore]

Well, where I have this hard foam, be it expanding foam or dpc foam there is definitely no gap. It is sandwiched between the 2 skins of brick.

 

[88v8]

It's Urea Formaldehyde foam. It doesn't bridge the cavity because it is not absorbent.
However, it may allow moisture to creep across at window perimeters if there are any cracks or openings around the windows.

The externally bridged dpc - the cement plinth - could have been a significant part of the problem. It allows rising damp - which does exist - to bypass the dpc and depending on the water table and porosity of the brickwork, the damp canl then climb up the wall, soaking through the external skin. How it then gets to the internal skin depends on the wall construction. There may be structural joins, ie not a complete cavity, or the wall ties may have been badly placed or angled downwards.
In 1920, cavity walls were in their infancy.

That said, our 1920 house had a cement plinth across the dpc ab initio, and no damp. But it was lime rendered.

The external render, if it was applied in the 80s, I would be surprised if it were lime. The classic test is to drop a chip of the render into vinegar. See
https://www.google.co.uk/search?q=how+to+tell+the+difference+between+lime+and+cement+mortar&oq=lime+morta+test+vinegar&gs_l=psy-ab.1.3.0i71k1l4.0.0.0.7505.0.0.0.0.0.0.0.0..0.0....0...1..64.psy-ab..0.0.0....0.mYMSxXepnQw#kpvalbx=1&spf=1508401425621

If it's cement. it will exacerbate any problems by preventing the wall from breathing, so it should be hacked off and the wall re-rendered in lime, that is to say Natural Hydraulic Lime. 'Lime' does not mean adding a dollop of hydrated lime to cement, as some builders seem to think.
At the junction of your house and your neighbour's, the damp may still creep across if he/she does not take similar measures.

As to the wallpaper problems, it will take a while for the walls to dry. As has been said, a month per inch thickness as a rule of thumb. Once the wall is dry - not before - all damp internal plaster will need to be removed as it will have salt contamination and the salts will continually reappear when prompted by internal moisture - from kitchen, shower, tumble dryer. No need for special plaster, just redo it in gypsum.

It can be hard to remedy damp. If it is a problem across the estate, that suggests a basic fault in design or materials or execution. One would have to think whether one wishes to persist, or cosmetically patch it up and move on. In a unique Period house, persistence may be the only way.
In a semi, one amongst millions, one may decide to pass the parcel, so to speak. Life is short.

Ivor