Moisture Testing

[Parm]

Is there any one here that knows anything about moisture testing of installed construction materials in a residential setting ?

Ive got a two pin type meter with settings for various different substrates, ie wood, gypsum, concrete screed etc etc. It comes with a table detailing what is dry, at risk and wet. I want to know where this criteria comes from

Thanks

Parm

 

[brightspark]

basically its like a megger insulation tester damp meter they will be calibrated on known materials and the chart will give u the acceptable levels to be ok

 

[Parm]

Yep, got that, I have a meter made by Testo and come with a calibration certificate. I want to know which document the evaluation criteria come from. Need to be able to quote exact source of information that details what is dry, at risk or damp.

There is a chart in the instruction manual but no information as to where the data is taken from

 

[WorkshopChris]

I just had a look on :- http://www.isse.org.uk/surveys/moisture_meter_testing
as i through there might be some info or links to data but cant see anything, if i remember where i have seen what i was looking for i will forward it to you.

 

[Paul99]

I've always assumed the meters were simply calibrated against in house samples of known humidity. How that relates to real world substrates though is another thing e.g. it's well known that salts that are deposited upon retreat of previous damp issues impact massively on electrical resistance and hence the displayed humidity could be massively over/under estimated. The instructions IIRC for our cheap moisture meter mention several times that readings are only an indication of the likely humidity - the accuracy of which depends greatly on the electrical conductivity / resistance of the material itself. My guess is that you will struggle to find data sheets used in the calibration for these cheap resistance based meters and unless you can calibrate it yourself against very very similar substrates that have been sent for analysis a rough guess as to the likely humidity is about all your going to get. It'll be interesting to see what you find out though...

 

[Parm]

Thanks, I'm dealing with a situation where a muppet has measured something and reported it being so wet that the place is uninhabitable. Unknown to me at the time I was invited back the second day to conduct the same texting, and guess what I found nothing. Even using the basics all was touch dry.

I'm confident in my work and now expecting this sorry saga to take a turn where I may be questioned. Just need to be sure about data sources. Saying it was quoted in the instruction isn't good enough. Plenty of anecdotal information on the net that agrees with my findings but just need to be able to quote a specific source

 

[Parm]

I've always assumed the meters were simply calibrated against in house samples of known humidity. How that relates to real world substrates though is another thing e.g. it's well known that salts that are deposited upon retreat of previous damp issues impact massively on electrical resistance and hence the displayed humidity could be massively over/under estimated. The instructions IIRC for our cheap moisture meter mention several times that readings are only an indication of the likely humidity - the accuracy of which depends greatly on the electrical conductivity / resistance of the material itself. My guess is that you will struggle to find data sheets used in the calibration for these cheap resistance based meters and unless you can calibrate it yourself against very very similar substrates that have been sent for analysis a rough guess as to the likely humidity is about all your going to get. It'll be interesting to see what you find out though...

The meter ive good (a good quality unit) measures electrical conductivity across two pins. You have to tell the meter what substrate your poking into as different materials contains differing levels of intrinsic moisture. 12% in wood is dry, where 12% in plaster board is sodding wet

And it's not the calibration sheet I want, I have that from the manufacturer. I'm after the guidance document that indicates what an acceptable level of moisture is in varying products.

Some kind of reference table published by a reputable agency or organisation that I can compare my results against and make an evaluation

 

[malcolm]

Have a look at the Heritage House website. Fellow there has a lot to say about these damp meters and not much good. Salts can have more effect than water.

 

[Parm]

Have a look at the Heritage House website. Fellow there has a lot to say about these damp meters and not much good. Salts can have more effect than water.

Yep ive seen that this after noon.

Bit more info, the situation is a new build and absolutely bone dry. It's social housing and one of the Tennents wants to move into another flat. Council has said no so the tennant is kicking up a stink and commisioned her own survey, by some knuckle head who doesn't know what he his doing. He's put a report together showing that the place is so dripping wet that you'd basicaly be living in a swimming pool.

Client has been a little naughty and commissioned me to do the same works, but failed to explain any of the previous stuff. My assessment is that the place is bone dry as confirmed with some quitevtechnical testing of airborne fungi and bacteria.

Next stage is that I will be required to present technical evidence and challenge the rubbish produced by the other party. Thing is now I need to know which building control document, guidance note etc makes reference to acceptable moisture conditions in specific materials.

This gonna be a fun project as the other party is a self appointed expert and member of a trade organisation that he's set up from his spare bedroom. Ive looked him up this afternoon and he's a one man band with a mostly made up CV that would be excellent if he was applying for a role with ghostbusters.

These resistance type meters are actually quite good for my specific application but like with most things these days no one knows how to use them correctly. "It has a digital display so reading must be correct"

Ive looked at the instrument used in the photos provided, it's a great bit of kit made by a reputable company called Protimeter, however the model that has been used is designed for measuring moisture content in felled timber that's drying out. It has no settings or accepted calibration curve for measuring moisture in construction materials. totally the wrong type of instrument has been used in this application

I'm going to be asked to challenge the work of the other party and just doing my home work, getting sources of info etc, reference documents and so on

I know I'm right on this one and quite looking forward to ripping the other party a new one !

 

[J.B. Welding]

I'd put a cap of 10-12% max moisture throughout a house, I think things like door frame timbers/facings are around 7% in a dry house, the plaster should be a bit drier than that, where the mildew is that's upto 20% at a guess, then there's the point where the plasterboard starts running down the walls called the 'meter no longer required' point. A meter should have a calibration for relative humidity and if it doesn't then it can easily swing 5-10% due to that alone.

 

[J.B. Welding]

I recon that fungi test is more court worthy than a basic moisture meter..good enough for firewood though, on an average day in China, relatively speaking..

 

[TechnicAl]

I think they work on conductivity. The higher the moisture the more conductive it is. Problem is some materials have a level of conductivity. We couldnt use them on welding rod coatings as the readings were all over the place.

We used weight loss but we knew what was in there.

 

[Parm]

I think they work on conductivity. The higher the moisture the more conductive it is. Problem is some materials have a level of conductivity. We couldnt use them on welding rod coatings as the readings were all over the place.

We used weight loss but we knew what was in there.

That's proper science

 

[malcolm]

Weight loss is how the old house bunch do it. Weigh plaster sample removed from wall then stick it in the oven and weigh again once water has gone.

At least good surveyors do it that way when asked. Most of the time it is bleedingly obvious if there is a problem and tests are not required.

 

[Parm]

Details that came with my instrument give criteria for gypsum based plasterboard as follows

2% or less is dry

2-4 is at risk

greater than 4% is wet

I need to know where this is taken from. For me saying that this is what came in the instructions of the meter isn't good enough and doesn't provide any traceability

 

[Parm]

Weight loss is how the old house bunch do it. Weigh plaster sample removed from wall then stick it in the oven and weigh again once water has gone.

At least good surveyors do it that way when asked. Most of the time it is bleedingly obvious if there is a problem and tests are not required.

Do you need a damming report for your insurers following your recent episode. I know an "expert" that will give you a report showing more than 100% moisture in anything you want lol

 

[malcolm]

Don't use that meter to measure damp. It will be professionally embarrasing for you if questioned. Not how these things are checked unless you are selling damp proofing.

 

[Parm]

Don't use that meter to measure damp. It will be professionally embarrasing for you if questioned.

I was referring to the other party that I'm looking at,

I'm no expert with this but in learning my self, I've asked a few basic question and thrown the storey put together by the other team wide open, it's going to be quite embarrasing as they have gone to town with a major article in a local paper

 

[wookie]

Thanks, I'm dealing with a situation where a muppet has measured something and reported it being so wet that the place is uninhabitable.

Sounds like the same muppet that condemned a boat for osmosis because he measured the dampness in the hull with the same sort of meter, the only problem was the boat he was testing was a race boat with a carbon fibre hull.....

 

[tomsutton529]

To answer the original question, don't the ISO Standards set out the guidelines for this kind of stuff.