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By phil.p
A friend some forty years ago had a problem with "rising damp". He parted with a lot of money having a chemical dpc put in one summer - great, he though, problem solved. Until the water started running in through the wall above the dpc - it was coming through rendering defects much higher up the outside of the wall and tracking down through. The dpc had stopped it going to ground. :D
By Jonathan S
Another Dampey story.

A client asked if I could take up her engineered teak floor up, when I asked her why, she tells me they have rotting skirting boards and there builder tells her they have a leak in there underfloor heating and it all has to come up and be replaced
My natural investigative mind asks her if she been adding any water to the underfloor heating, she hadn' I got her to hold with ripping her floors up and find what was really happening. We investigated all the usual plumbing and duct work and found nothing.
Scratching my bald head I asked a friend/ builder to help....he came to site and spent some time investigating, his verdict was the Spanish tiled roof is the source and needs repointing.....the clients didn't belive it, but I got them to trust the information and they eventually arranged to have their roof repaired.....solved the problem!....the water was coming in via the roof, travelling along a concrete ceiling down a wall and into the floor, it showed no evidence of any damp until it was in the floor......

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By novocaine
the only true way to test for damp in plaster and brick is to drill out a sample then use a calcium carbide chamber. basically when moisture comes in to contact with CC it reacts and produced acetylene gas, the pressure of which can be monitored and correlates to the amount of moisture in the sample.

the muppet with his resistance probe isn't doing you any favours by using it, as already alluded to above there are many things that can result in low residence and have nothing to do with moisture.

if you now have a concern, contact 3 other companies (preferable one of which should be a building surveyor) and get a range of opinions.

cavity wall insulation extraction is the new cavity wall insulation installation which was the new DPC injection. mostly a con that can result in no end of problems for the property and normally installed by a bunch of cowboys who have no regard for the property, it's construction or it's environment. (having just been stung for 2k to have it removed because of the PO who got a grant to do it, on a property with pourous warrington brick from the 1940s and a gable end that's exposed to driving rain with a painted finish, I rather dislike the whole damn industry)
By Jacob
I know not everybody agrees but I think rising damp is a bit of a myth - it's more a case of falling damp descending through a structure until it meets a saturated level usually about ground level, at which point it backs up a bit and can stay higher than ground level.
PS though having now read this maybe I'm wrong, but it's not as common as folk like to think.
By MusicMan
Thanks to everyone for their advice, which is very helpful. To answer questions: there is no trace of damp inside the house by mould, smell or feel. My original concern was following press reports that blown rockwool cavity insulation could develop tracking paths for moisture over time (it was done about 25 years ago). There was no trace of this even from the representative of the firm that contacted me. He claimed that the higher readings of damp low down were indicative of rising damp, hence my due diligence on this forum. The two-point probe readings he took are the only "evidence" of this.

Following advice here, I have gone over the house more carefully and thoroughly, using my own wood moisture meter, which is a pinless type, in principle sampling a larger volume. There is a problem calibrating all moisture meters in absolute terms, so I only did comparative measurements. Fortunately I had skirting boards of the same wood both on external walls and on internal ones, both unpainted. I could not find any systematic difference between the two.

The pinless type probably also gives a better reading on walls than the pin type, though calibration is very uncertain. However, I could not find any systematic variation with height on the walls either.

I conclude (along with the great majority of repliers here) that the firm trains its staff to use inappropriate meters, which are likely to give false positives.

The most that might be worth doing is repointing the brickwork below the render (looking at MikeG's comments). Looking at it now, the bricks are probably not covered by bitumen, but by a relatively thin black paint - hard to tell. I attach some pics of the brickwork. For the last one I dug down a bit to remove soil (which is sandy and quick draining). I must admit I cannot tell where the DPC occurs! Anyway, comments on these will be welcome.

house dpc - 1.jpg
house dpc - 2.jpg

house dpc - 3.jpg
house dpc - 4.jpg

house dpc - 5.jpg
house dpc - 6.jpg
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By Phlebas
I used to be the head partner of the Scottish professional department of one of the big surveyors. My equivalent in the building surveying department would regularly throw away the two pronged moisture meters if he found any of his staff using them (trained by other firms, t’chah, charlatans, every one of them). They are simply unreliable (at best) if used in masonry, unless you really know what you are doing. He was of the opinion that relying on one by itself was tantamount to an admission of professional incompetence.
User avatar
By toolsntat
Pictures 4&5 look to be showing cables clipped under the render stop beading which generally has a bottom bevel to throw water away from the underlying bricks and mortar.
Surely this could allow the water to track back onto the bricks and mortar (possibly above any dpc ?)
Cheers Andy
By AJB Temple
If you are still o the opinion that there is in fact damp (questionable) I think I might be tempted to chip off some render and see if you can locate the dpc. Is the render bridging the dpc?
By Woody2Shoes
MusicMan wrote:....there is no trace of damp inside the house by mould, smell or feel....

On that basis, I would strongly question whether you have any kind of problem worth worrying about! If it were me, I'd forget the whole thing.

I'm guessing that the DPC will be pretty much at the same level as the horizontal render bead. The render appears sound. The pointing does look a bit odd/tired but seems sound enough. The ground level appears to have been raised in the fourth/fifth pictures - where there's gravel/paviours - normally you'd expect to see 150mm (two brick courses'ish) between DPC and ground - to reduce risk of backsplashed rain hitting the wall above DPC (but the masonry above DPC appears to have proper rain protection from the render in any case).

Seriously, I'd find something else to occupy my mind. Cheers, W2S
User avatar
By MikeG.
Again, just a quick skim of the photos (I'm really busy)...... if the bottom of the render is at DPC level, then there are some places where your ground level is too high. A DPC must be a minimum of 150mm (2 brick courses) above ground level. Ideally, too, your ground adjacent to the house shouldn't be hard, because this allows rain to bounce up the wall. So, although you seem to have no damp issues, you do have potential problems and should consider lowering the ground level and changing to a porous surface.
By MusicMan
Thanks again for advice. I have just told the firm that we are not going ahead with their quote.

Andy/Mike thanks for the advice re 2 brick courses above ground before the DPC. The gravelled part is easy, as it is just a border bed with a few ferns and box bushes. The gravel is deep and some can easily be removed. With the block paving, I can remove it along the wall and replace with gravel at appropriate depth, and also re-route the cables as suggested.

Most helpful.