Damp

[AndersonC]

From my experiences in a relatively old house, a key factor which can contribute to the passage of damp into an internal wall is a blocked/bridged cavity. This allows damp to be bridged in from the external leaf to the internal leaf, but is not rising damp. The surveyor comes along, places his unsuitable damp meter (designed for timber) on a piece of plasterwork and declares that the property has rising damp, and that the best method is to install a chemical dpc and hack off 3' of plaster all over the house (I am sure these surveyors hold shares in the chemical & plastering companies).

In our house parts of the cavity have been filled with bits of bricks etc etc from incompent window fitters knocking stuff inside the cavity and no amount of chemical injection would prevent moisture travelling though this rubble from the outside to the inside. This can be made worse by incompetent use of SDS drills during chemical injection with bits of brick being 'popped off' the back of the walls into the cavity.

Before I discovered this forum, I made the costly mistake of having a 'dpc' injected and months later, during a discussion over a pint with a local builder (i.e. a person who builds houses not just drills holes and put chemicals in them) was told that the injection technique is a complete waste of time (oh, and money too). I'd have been better off getting the cavity cleared out and putting new/more airbricks in (it's surprising how well air can keep things dry). He informed me that if he replaces a DPC then he removes a course of brickwork (in 3' increments), clears the cavity, puts a physical DPC in place, replaces the bricks and re-points. A far more thorough method in my opinion.

A question for dano1779 - if these injected dpc's are as good as the injection companies would have us believe, then why the hell do most firms only offer a 10 year guarantee?

 

[Softus]

I love you AndersonC, and I want to have your babies.

 

[AndersonC]

By eck!!!

I'll be keeping an eye on this thread today - interested in seeing the answers to the 16 questions Softus asked, and also it would be nice of dano1779 would enlighten me on how the injected 'slugs' of chemical, spaced about 120mm apart, form a continuous moisture-resistant layer within a brick wall.

 

[Softus]

To explain, and to be slightly less weird about it, I have long-standing in interest in breaching the circle of lies that surrounds chemical damp-proofing. If you're interested, and if you have some time, you might want to peruse this topic:

//www.diynot.com/forums/viewtopic.php?t=34549

 

[masona]

rossage, do you have a cavity wall, if so, this may interest you although I agree with Softus it's most likely water behind the rendering.

 

[ColJack]

1. What was the ground level outside the damp wall, relative to the old DPC?
2. What was the ground level outside the damp wall, relative to the new DPC?
3. What was the internal floor level, relative to the old DPC?
4. What was the internal floor level, relative to the new DPC?
5. What type of ground was outside the damp wall?
6. Had the house been unoccupied for any period of time before he moved in?
7. If so, for how long, and at what time of year?
8. Which direction was the outside of damp wall facing?
9. What area of the country was this?
10. What was the construction of the damp wall?
11. Did it have a cavity?
12. Was the wall rendered, or covered by any means, on the outside?
13. If so, what was the state of repair of that covering?
14. Did it have any insulation in the cavity?
15. How old was the house?
16. What was the construction of the floor next to the damp wall?

I'll do my best but since i'm not at his house and it was about 12 years ago i'll answer the best i can...

1. there are 2 steps down from the front door and a ramp from the rear so about 12-15 inches..DPC was one brick down from the floor level so about 7-10 inches ( damp was at the rear, where the height was the highest..)

2. the new DPC was injected in the brick above the old DPC.. ( looked like it anyway.. 2 little holes in each brick, I'm assuming it was that.. )

3. about a bricks height..

4. about half a bricks height...

5. paving slab walkway, about 5ft wide..then drop to next door..

6. only about a week..

7. see 6. and it was May..

8. google earth grid reference for my brothers house [code:1]52 28'32.09N, 2 08'39.95W[/code:1] the north west corner was damp..

9. see google earth for exact location, jus put the above co-ords into search.. the cross is on his house..

10. brick?

11. yes.

12. no.

13 N/A.

14. no

15. no idea.. but it's been up for a long time, not a new build..

16. joist and floorboard..

there you go, hope that helps..

just for my own wondering now, I'm going to take a section of wall that will come from a house recently knocked down round the corner and stand them in a bucket with 3 inches of water to see if the top bricks get damp.. .. i'll put it in my shed and carefully top up the water every few days if it starts to disappear...

 

[AndersonC]

The water will disappear due to evaporation out of the bucket!!!!!!!!

This won't tell you a lot about water entering the brick/mortar. All it will tell you is that the water level goes down, which is more likely going to occur by evaporation than the water mysteriously climbing up a chunk of brickwork. Especially as we're having a reasonably warm May.

 

[oilman]

For those having difficulty accepting the non-existence of rising damp, go and have a look at a stone bridge (preferably a porus one like sandstone, crossing a river, and with a column in the water) See how high up the stonework the water creeps above the river level.

 

[Softus]

To be fair to the doubters, is a stone bridge a realistic representation of a baked clay brick wall?

 

[oilman]

Well they could go and search round the canals for bricks in water; plenty of them there. But sandstone will soak up water. Railway bridges aren't much use as they used engineering blues. Garden walls are another possibility, built without DPC, how far up does the damp get?

 

[Thermo]

no not really!

mind you how high are we saying water has to creep or not creep to be regarded as rising damp?

 

[oilman]

It can't creep beyond the mortar joint above the block/brick that sits in the water.

 

[Softus]

mind you how high are we saying water has to creep or not creep to be regarded as rising damp?

I'm open-minded, but, given that a modern DPC is intended to be at least two courses above external ground level, I would say that anything over two courses could be considered to be RD.

 

[dano1779]

softus mate its people like you that cause wars i read your last discussion on rd all i can say is some people say it exists and some people don't.

 

[Softus]

softus mate its people like you that cause wars

i read your last discussion on rd all i can say is some people say it exists and some people don't.

None of the people who say that it exists, with the possible of exception of ColJack, has any evidence whatsover.

It's rather odd that there's only one person on the forum in the last 18 months who's able to answer some basic questions on an example of a possible example of RD, n'est-ce pas?