Ask a Tradesman
QuestionDamp patches around chimney breast
I think I have an interesting one for you all...
I have had a problem with damp patches appearing around my ground floor chimney breast and I would have though I first noticed an issue around 2 years ago. This is an INTERNAL wall and the construction is SINGLE SKIN brick. In June 2011, I commissioned an independent damp survey (CSRT qualified surveyors independent of any supplier) to try and identify the root cause of the problem.
The surveyor took damp measurements of the affected wall and created a damp profile. The moisture meter indicated elevated readings ranging from 70 - 90% in the plaster of the chimney breast and 40 - 60% in the plast of the adjacent wall. The skirting boards were 20%. Up to 1m the readings are fairly consistent and at approx 1m the damp readings stop entirely.
At my instruction floorboards were not lifted due to an existing laminate floor that I can't afford to replace at present. Samples of brickwork were not taken and the surveyor inspected the house from the outside but did not get up onto the roof or go into the loft.
The survey report identified the "cause" as being rising damp due to a missing or ineffective dpc in the chimney breast. Also possible bridging from the concrete hearth and associated earth mound allowing moisture to track up the brickwork and plaster. Unable to confirm whether the hearth is insitu due to the flooring.
Recommendation is to install a dryzone or vandex dpc in the bottom row of brick above floor level and replaster with sand+cement incorporating salt inhibitor. Plaster not to project more than 25mm below top of new skirting and min gap to floor of 25mm.
HOWEVER, from visual inspection over a period of time, the damp patches on the wallpaper gets worse very quickly during periods of heavy rain and gradually dries out over a period of several weeks when there is a dry spell (all too rare in north Manchester!).
The gas fire came out today and the hearth behind was full of rubble and soot. I have cleaned all of this out. I have had a couple of lads come out to quote for the
So then based on the above, is my problem:
a) Rising damp as diagnosed by the surveyor
b) Penetrating damp from a leaking chimney
c) Condensation being hygroscopic salts in plaster drawn through from brickwork behind.
d) Some combination of the above/ other
And based on that diagnosis. Do I:
a) Hire a dpc Contractor as per recommendation
b) Get a roofer to see what is what up top and fix any problems there as a first try.
c) Buy a dehumidifyer and run it hard for a few weeks.
Sorry for the essay, hope you found it an interesting one, any more info just ask, look forward to seeing responses.
Your problem is definitely rising damp. I can confirm this, as you have described that the damp readings stop at 1 meter. Rising damp will only rise to a maximum of 1 meter high.
Even if you have a new damp proof course installed, the plaster above would still need to be removed and replaced with a damp proofing plaster system.
Once plaster is wet/damp, then it will never dry out, even with dehumidifiers. This is due to the high salt content in the plaster/render, and the moisture within the bricks themselves.
For more info please take a look at www.actdampandpreservations.co.uk.
A.C.T Damp Proofing & Preservation's
A.C.T Damp Proofing & Preservations 1st Oct, 2011
Your problem is probably a combination of issues, chimney breasts were usually constructed with no DPC, therefore when the roaring hot fire which used to pull all the damp up the flue was removed, rising damp could have taken hold however the problem with chimneys is that they often have a rubble filled void either side of the fire opening, this makes injection unsuitable as the moisture would rise through the rubble and beyond the dpc penetrating the walls from the inside- out. Also you could have problems with interstitial condensation and with your description an open chimney allowing rain/moisture to leak down the flue and collect in the debris at the bottom.
Sorry if I threw a few more spanners into the works, but a far deeper investigation is required to get to the bottom of this.
And fyi rising damp can go well beyond 1m depending on wall construction, and the only way to tell if the damp is rising or not is with a calcium carbide test.
Mike Davison cssw
Dryspace Maintain Ltd
The damp and condensation experts
Dryspace Maintain Ltd 13th Oct, 2011
hya its rising damp cos it only rises average 1mtr ,you can get a slurry t protect ur internal furnishings ie wall paper n decoratin but will not cure the problem till you get new dampfroofing injected to affected areas ,also check that thers a cowerly on your chimley pot
Jason Wright Property, Maintenance and Joinery 14th Apr, 2012
Hi dave. Got to agree with. act. sort out rising damp issues and then check chimney flashings for water ingress ,these are the two main problem areas with chimneys . Don't waste cash on de humidifier , Walls will dry when plaster off, to do works etc so long as not soaking. Cheers mark
M N M PROJECTS LIMITED 6th Oct, 2011
Rising damp is the common term for the slow upward movement of water in the lower sections of walls and other ground-supported structures by capillary action. Although rising damp of up to 5 metres in height has been observed the height of rise is typically much lower and is rarely above 1.5m. Rising damp has been a widely observed phenomenon for at least two hundred years. Rising damp is deemed controversial because it is often misdiagnosed in buildings.[Hutton 1] Many misdiagnose a wall stain as rising damp instance due to misinterpreting the visual evidence of the wall and the readings of moisture meters.[Hutton 1] There is also strong evidence to suggest that it was a problem understood by the Romans and Ancient Greeks.
mid-uk Property Solutions 7th Oct, 2012
I aliways use sulphate resistant cement around chimney breasts to allow for the soot content
Building services 8th Jan, 2013