Author Topic: Renovating a victorian end of terrace house  (Read 950 times)

Renovating a victorian end of terrace house
« on: November 19, 2020, 07:47:38 pm »
Anyone done this? While I don't think that it will work accurately to translate into moisture content, you should be able to get comparative readings from various points on the wall to build up a picture. I'm thinking of knocking a couple of masonry nails into a piece of wood to use as probes for consistency, using my old Fluke 29 Mk II which happily measures up to 10Mohm.

The objective is to intelligently challenge a damp survey which identified damp on an internal (party) wall but not on the external wall of Miss Ham's new abode (as of tomorrow). I suspect that damp, if present will have an alternative cause other than defective damp course which will be a pain to rectify on a party wall but is linked to a mortgage retention.

Feanor

  • It's mostly downhill from here.
Re: Using a multimeter as a damp meter
« Reply #1 on: November 19, 2020, 08:06:51 pm »
If you are wanting to challenge an existing survey, rather than just mess around for your own fun, then I don't think there's much mileage in trying to calibrate a generic meter to dampness.
I think you'd need to use a recognised dampness meter.

If you want to mess around for fun, then I'd say knock yourself out.
I have no knowledge of how damp meters operate or are calibrated.
What voltages to they use?
Multimeters typically use pretty low voltages.
Insulation testers use hundreds of volts.
These will give different answers.

Presumably, dampness meters have some standard method which will use some certain voltage.
And then, what calibration curve to they use from resistance to dampness?
It may well not be linear.

So no, I don't think a simple fluke meter will be able to provide a body of evidence to be able to challenge an existing dampness report.


Re: Using a multimeter as a damp meter
« Reply #2 on: November 19, 2020, 09:06:52 pm »
"Challenge" might be too strong a word. The survey wasn't too bad and I've no reason to suppose they didn't find damp, and getting them to do the injection would be the easiest move. But. When I look at the area they have indicated as needing it, it looks to me that they have waved their meter around and assumed stuff that frankly doesn't make sense.

Picture shows the situation, entire rear part is "condemned" for rising damp. Not the rest of the party wall. Includes a ramshackle lean to that has may have rising but deffo has  falling damp and is clearly going to be removed. There may be damp on the outside wall, for sure, but I reckon any damp on that interior wall is far more likely to be from the shower room, or penetrating from the lean to edge.

Not to scale  ;D dots signify areas marked as having rising damp.

outside wall (end of terrace)
   =============================
   |                                                                  |.................................................
   |                                                                  |======================
   |                                                                  |.                 |.                  |.          |.<<Ramshackle lean to on end
   |                                                                  |.                 |.                  |.          |.
   |                                                                  |.                 |.                  |.          |. GARDEN
   |                                                                                 
   |                                                                  | .                |  .......   ...... |.......... |.
   |=============================                  | ====  ==  | ====|.
   |                                                                  | .                |  .    Bath     |.
   |                                                                  | .                |  .    room    |.  GARDEN
   |                                                                  | .                |  .                |.
   ==============================================
           PARTY WALL (TERRACE)                           ....................................

Kim

  • Timelord
Re: Using a multimeter as a damp meter
« Reply #3 on: November 19, 2020, 09:10:40 pm »
I have had some success using a multimeter to crudely map the edge of a damp patch, to determine whether it was expanding or retreating after the leaky roof had been fettled.  I wouldn't rate it for much else.
Careful, Kim. Your sarcasm's showing...

Re: Using a multimeter as a damp meter
« Reply #4 on: November 19, 2020, 09:12:24 pm »

Presumably, dampness meters have some standard method which will use some certain voltage.
And then, what calibration curve to they use from resistance to dampness?
It may well not be linear.


The number of factors involved is huge - chemicals in the wall, temperature, etc etc but were I to square the wall off into 100mm squares and plot each one, I should get a good picture.... maybe.  So summat like wot Kim says, but it would be nice if there was some kind of correlation of moisture to resistance that could be used to calibrate. I'm thinking of soaking a patch and waiting 30 minutes to get a 100% reading.

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #5 on: November 19, 2020, 10:30:47 pm »
I do not have the answer but this may be of interest. Long term denizens of this forum may remember the many pages of damp related woe I have posted. During this fun time in my life I bought a moisture meter.
After the works were finished I ended up as per the picture below:
IMG_4576 by The Pingus, on Flickr

The light stuff at the very top of the chimney breast is old lath & plaster wall with a fresh coat of dry lime plaster on it. At the bottom, round the stove is where the lath was removed, replaced with some sort of fireproof mineral board and then skimmed with fireproof plaster. There is nothing behind that board in contact with the stone wall behind it so there should not be any transfer of moisture in that direction. However ever since it was done the top section has read 'dry' while the bottom section has read 'damp'. (And indeed after I painted it all with Claypaint that whole bottom section is a different shade of colour than the rest of the room  ::-) .)

So although I don't know what your daughter's wall is made of, from my own personal experience there is the possibility of (but not limited to):
Build up of lime plaster type debris at the bottom of the wall which is full of hygroscopic salts and will give a damp reading.
For example:
IMG_2894 by The Pingus, on Flickr
Or - No debris but a previously damp wall now contaminated with hygroscopic salts which will always give a damp reading by adsorbing it from the atmosphere.
Or - A funny reading because the wall is made of an odd material.

I do think that mapping the readings on the wall is a good idea. If it seems like it's worst at the bottom of the wall you could make some exploratory holes in the plaster and see if there's a shit load of debris lurking there like there was at mine.
Do not clench. It only makes it worse.

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #6 on: November 19, 2020, 10:35:42 pm »
Question - is there access under the floor?
Do not clench. It only makes it worse.

Re: Using a multimeter as a damp meter
« Reply #7 on: November 20, 2020, 06:05:06 am »
Ah yes - you had PHUN didn't you? This is somewhat different, I think. First off, completion is only at  midday today (!!  ;D ;D ) and examination has been limited during the pandemic (vendor is vulnerable) but even so. House is very much a "doer-upper" (l/h of the two l-u-u-u-u-uvly examples of pebbledash), built around 1900, all the terrace have coal hole basements, the area sits on gravel and my experience from a mile away is that even with a flooding cellar (we have an underground river nearby) our party wall of a semi stays bone dry at the top. I simply don't believe this party wall has rising damp. I'll be looking and initial poking later. (wall is brick, London stocks)

Re: Using a multimeter as a damp meter
« Reply #8 on: November 20, 2020, 11:24:36 am »
So, damp probe #1.

Stick the probes into a bit of wood that's been stored for years, open circuit, good. Drill then hammer in two masonry nails, connect up the meter, that'll be 14MΩ, thank you.

Damp probe #2

Use a plastic corner jointing block, drill, hammer, connect, open circuit, good.

Test by pushing into various walls. Discover that there is no apparent easy correlation. Very wet is something like 300kΩ or lower (about 2.5 cm separating). dry seems upward of 5MΩ. Stuff in between? who knows.

Re: Using a multimeter as a damp meter
« Reply #9 on: November 20, 2020, 07:46:51 pm »
Not massively helpful for mortgage purposes, but my experience of the 'damp proof' companies (one of the big national ones) is that they stick a probe on the wall, tell you that you certainly have rising damp, and charge to fix it, and when it comes back, stick a probe on the same walls and tell you that it's certainly not rising damp, and not their problem.

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #10 on: November 20, 2020, 07:51:36 pm »
Yes, that's what I read on the websites of heritage home specialists too.
Do not clench. It only makes it worse.

Re: Using a multimeter as a damp meter
« Reply #11 on: November 20, 2020, 07:57:29 pm »
The text

Quote
Rising damp
Observations and conclusions
Inspection of the lower wall areas identified on the diagram below found damp staining and a deterioration of the decorations
consistent with rising damp. The plaster appears to be affected by hygroscopic ground salt (nitrate and chloride) contamination.
Moisture meter tests indicated dampness extends to a height of approximately 450mm.

The reality:

To be confirmed tomorrow, but it looks like the photo showing the probe being used was in the lean to, which leaks like a leaky sieve with leaks. Most of the areas shown on the diagram are either inaccessible (tiled, behind cabinets which weren't removed) or - according to my meter at least for the party wall - bone dry.

There will be words, come Monday.

Re: Using a multimeter as a damp meter
« Reply #12 on: November 21, 2020, 08:00:07 pm »
This might be worth a read.
https://www.heritage-house.org/damp-and-condensation/the-ping-prong-meter-guilty-of-fraud.html
There are various other sites giving similar opinions.

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #13 on: November 21, 2020, 09:07:17 pm »
This might be worth a read.
https://www.heritage-house.org/damp-and-condensation/the-ping-prong-meter-guilty-of-fraud.html
There are various other sites giving similar opinions.


That's exactly the one I was thinking of upthread.
Do not clench. It only makes it worse.

LittleWheelsandBig

  • Whimsy Rider
Re: Using a multimeter as a damp meter
« Reply #14 on: November 21, 2020, 09:16:08 pm »
That webpage is spot on. The thing actually measured is resistivity which is affected by lots of factors. Blindly following numbers for most materials without understanding the complexities will lead you up the garden path.
Wheel meet again, don't know where, don't know when...

Re: Using a multimeter as a damp meter
« Reply #15 on: November 21, 2020, 09:43:53 pm »
I now know about Calcium Carbide sample meters..

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #16 on: November 21, 2020, 10:44:21 pm »
Do not clench. It only makes it worse.

Gattopardo

  • Lord of the sith
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Re: Using a multimeter as a damp meter
« Reply #17 on: November 21, 2020, 10:57:23 pm »
Having done a few courses when I was an RICS surveyor.  Those meters are pretty pointless without understanding the results.

Also rising damp is a myth, there are lots and lots of houses without a damp proof course and no moisture.  If you really want to waste money, chemical damp proof courses are proof of snake oil.

Re: Using a multimeter as a damp meter
« Reply #18 on: November 22, 2020, 08:03:56 pm »
Yes, rising damp cons were discussed at length in the link ∆ damp problems being mainly down to condensation.

Re: Using a multimeter as a damp meter
« Reply #19 on: November 22, 2020, 08:40:40 pm »
Well, I trolled around poking a bit more today. The surveyor completely missed the area that was blown with paper falling off where the roof tiles were missing and water has been pissing in, as well as another bit of obvious damp on the flank wall, which turns out to be there neighbor roofing over the alley (theirs) and the run off from about 8m flooding down the wall.

Oh, and there is one bit of damp on the party wall, but at an of location which my guess the cause is, the neighbor's sink.

An interesting conversation to be had.

Mrs Pingu

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Re: Using a multimeter as a damp meter
« Reply #20 on: November 22, 2020, 10:09:27 pm »
Ha. Not surprised. Let's face it, the surveyor probably spends what, 30 mins on your average house survey?
Do not clench. It only makes it worse.

ian

  • feat. Undead Jess & Finestre, Queen of Hell
Re: Using a multimeter as a damp meter
« Reply #21 on: November 23, 2020, 09:31:56 am »
We found the Word template for our survey (seriously, you can buy a ready-to-compete house survey), a literal case of fill in the blanks. We filled out our own version with exciting stuff like 'beavers in the kitchen' (if we sell this place, we should include that). He was actually a nice and informative chap when we talked to him, but the actual survey (the basic building kind) was useless. I know you get what you pay for, but it still about £600.

(We found damp in the kitchen, but the cause was condensation behind kitchen units and a long-term leaking dishwasher connection).
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Gattopardo

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Re: Using a multimeter as a damp meter
« Reply #22 on: November 23, 2020, 05:27:11 pm »
Yes, rising damp cons were discussed at length in the link ∆ damp problems being mainly down to condensation.

Condensation or water leaks. 

Oh I had rising damp in a third floor flat.

Gattopardo

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  • Overseaing the building of the death star
Re: Using a multimeter as a damp meter
« Reply #23 on: November 23, 2020, 05:28:23 pm »
Ha. Not surprised. Let's face it, the surveyor probably spends what, 30 mins on your average house survey?

On a valuation survey they can even be a drive by.

Gattopardo

  • Lord of the sith
  • Overseaing the building of the death star
Re: Using a multimeter as a damp meter
« Reply #24 on: November 23, 2020, 05:29:10 pm »
We found the Word template for our survey (seriously, you can buy a ready-to-compete house survey), a literal case of fill in the blanks. We filled out our own version with exciting stuff like 'beavers in the kitchen' (if we sell this place, we should include that). He was actually a nice and informative chap when we talked to him, but the actual survey (the basic building kind) was useless. I know you get what you pay for, but it still about £600.

(We found damp in the kitchen, but the cause was condensation behind kitchen units and a long-term leaking dishwasher connection).

The surveyor doesn't get £60, more the pity.