Damp

[Trommel]

I own a mid to late 18th Century brick terraced cottage which has been largely unoccupied and unheated, although furnished, for most of the last decade, and has never had central heating fitted.

There is damp in the sitting room, and particularly around the chimney breast, to a height of about 12" from the floor - the builders who were due to install floors and heating suggested a damp survey before proceeding. It's currently fairly bad (paint has peeled, slight crumbling), but isn't worsening.

I had the usual free survey, which confirmed only that there was damp in the walls (no surprise). The recommendation was, as expected, a chemical DPC throughout (the front wall of the property at least has at some point been treated previously, although it obviously isn't working).

The roof, gutters and chimney are all sound.

I don't want to waste money on a chemical DPC which may not work - how likely is it that with some heat and ventilation it may dry out of its own accord? What else could I try?

Thanks in advance.

 

[Trommel]

Just found the damp FAQ. The property has cement floors throughout - I don't think that there's a practical way to change this.

 

[MdB]

What is the ground level like outside? It should ideally be 300mm below the inside level assuming the foundations go down that far.

I have a similar problem with a concrete floor forcing the water under the floor up through the walls. My first line of attack is to lower the outside ground level (300mm above inside floor level in places) and then to french drain so as to hopefully lower the water table under the house.

If this doesn't work, I may remove a section of concrete floor around the walls and replace it with limecrete. It that fails, I'll get someone (that doesn't work for a DPC company) in to work out what to try next.

 

[Trommel]

Floor level is a couple of inches above pavement level (the front door opens directly to the footpath).

I'm pretty sure the damp wasn't an issue when it was occupied, so I may just press on and see what happens.

I imagine that the central heating will draw out a lot more moisture ...

 

[Moo]

I wonder how thick the concrete is?

 

[Trommel]

Not very I would guess. The property has never had boarded floors, upstairs or down.

 

[Moo]

"a mid to late 18th Century brick terraced cottage" that has "never had boarded floors, upstairs or down"

What did/does it have upstairs, then?

 

[Penners]

As the house has been empty and unheated for ten years, it's not a bit surprising that the place is damp. You say that the chimney breast is a particularly damp spot - is the chimney still open at the top? if so, then rain will have been coming down inside it for ten years, with no heat source to dispel it. If you're not going to use the chimney, I should get a ventilated cowl fitted to it.

I share your view that warmth and ventilation will probably make a huge difference, although you'll have to be patient - results probably won't be quick. If you want to speed up the process, you could hire or buy a dehumidifier, but don't be tempted to suck all the damp out too quickly. Just tackle it gently and patiently.

Given the age of the property, I presume it's got solid brick walls? If so, and given that you've mentioned the pavement outside, rainwater bouncing off the pavement on to the walls could be soaking through. And have you checked the pointing of the brick walls?

I certainly wouldn't spend money on injecting a DPC. Damp problems like this need a try-it-and-see approach, one step at a time. The first step - warmth and ventilation (and a chimney cowl if necessary) - stands a good chance of success.

 

[Trommel]

Thanks - I had considered a dehumidifier, just to see what the effect was.

The floors are cement/concrete - I assume upstairs at least was lime ash or similar once.

 

[Matt Green]

Chimney breasts are frequently contaminated with hygroscopic salts brought about by the burning of coal within them.

The salts will absorb water from the air making the internal finish damp and spoiling decorations. Chimneys are usually exempt from chemical DPC guarentees for this reaon (really: check the fine print).

If the house was recently unoccupied the heating would be off...and the temperature in the house would be low...and the relative humidity would have increased...and the air moisture loading would have increased...and there would be more water in the air for the brickwork to absorb.

A theory, nothing more, but it fits the description.



Matt

 

[Penners]

Chimney breasts are frequently contaminated with hygroscopic salts brought about by the burning of coal within them.

Matt - just as a matter of interest, is there any way of neutralising these salts?