Advice please i have been flooded.

[gps]

Hi I was flooded at my property last month. I have a company in taking readings on the cob walls that have now been stripped of the plaster /render, they are not very upfront with the info after their checks so Im hoping someone on this site may know what sort of readings they should be getting in the walls to say they are dry.
I know the last check they did i saw some figures 35 - 55.

Hope there is someone out there that may be able to help.

 

[MdB]

How were the reading made? Was it with a 2 prong device stuck into the wall or was a hole drilled and a sample taken and put inside of a machine?

If the former, then a measurement of resistance was made rather than a measure of moisture content and the result could mean anything and it depends on what the wall is made from. With cob, this could mean all sorts of things. Ignore the results and get somebody in who knows about making proper measurements.

If the latter, then I can't comment on the readings but at least they are using the right machine.

When you get around to replastering / rerendering, make sure that no cement or gypsum is used. It can be damaging to cob due to its ability to trap moisture. Use lime instead.

 

[gps]

Thanks for the advice. When taking readings they did drill test holes and used something that was called a probe which measured the relative humidity and the temperature.

 

[Matt Green]

Have they drilled any holes in an unflooded completely dry area to privide 'control' readings? In other words they need to know what the building's normal state is so they can report when the flooded area have returned to it.

35 and 55 sound like relative humidity readings. They are percentages. At 100% the air inside the hole would be holding as much water as it possibly could at that temperature. There's no way of applying a standard across all buildings as those values will vary with the construction. The best way of using such devises, these and resistance moisture meters, is to get a profile of the walls from as wide an area as possible and look for any trends over time and location.

Incidently, this sounds like an insurance company appointed contractor generating money by hacking plaster off. It's neither best practise or standard procedure, certainly not for a cob structure, unless the plaster was gypsum, as mentioned, which I am sure they checked before starting works....


M

 

[MdB]

Matt is one of the experts around here. Listen to him rather than to me.

 

[Schoolmarm]

Also I think I may be right in saying...................(I hope so).............The walls could be rerendered and replastered before they are dry anyway if the correct stuff, ie. lime is being used.
The first thing anybody would do before plastering/rendering is thoroughly wet the walls. :roll: Make sure you have an expert doing all this like Matt says.



If they have hacked lime plaster or lime mortar off then THEY ARE IDIOTS!!! It would have dried out nicely anyway.

 

[biffvernon]

35 and 55 sound like relative humidity readings. They are percentages. At 100% the air inside the hole would be holding as much water as it possibly could at that temperature.

Aren't those numbers rather low for what you describe, Matt?

 

[Lime]

It needs to be pointed out I think that older constructions are rarely completely dry.
Don't be fooled by inappropriate comparisons to modern expectations of building construction.
Also, going by the readings you have quoted, the cob appears relatively dry.

It is a pity that the plaster etc has been stripped off if it were lime based... inappropriate, damaging and unnecessary.
Don't have it replaced with a modern plaster (thistle, gypsum and the like) because I predict that you will have damp problems if you do.

 

[Matt Green]

35 and 55 sound like relative humidity readings. They are percentages. At 100% the air inside the hole would be holding as much water as it possibly could at that temperature.

Aren't those numbers rather low for what you describe, Matt?

Possibly not, although the analysis might not make for pleasant consideration.

Flooding, unless it's prolonged and severe doesn't penetrate the building fabric all that far for all that long. If the plaster they removed was cement it would have held back the water very effectively (as we all know it does, this time in a constructive way and from the other direction than usually discussed here). So the walls might not be all that wet at the core. The meter is reading the RH of the air within a cavity within the wall, not the % moisture content of the fabric. No air movement inside a cool wall and you could definitely see figures like that. Given that cob structures are almost damp by design it may be that those figures are not all that far from those anywhere in the house. Which means....

No, no, that's far too cynical. I'm sure they took readings immediately after the flood and again before the decision was made to remove the plaster. Otherwise, how would they know if it had been adversely affected? It must have been. The contractors have the client's best interests at heart. The client being, possibly, the big, faceless corporate insurance company. I mean- I'm only speculating.


M

 

[gps]

Thanks, all advice has been noted and will be followed.

This is a great site and members are very helpful.

 

[Jon Maine]

Was it fresh water or salt water?

 

[Gareth Hughes]

Cement and gypsum will make it collapse That is not an idle threat, and I wish I could find the photo I took 15 years ago that shows what happens when you start fussing about damp in a cob building (basically, a picture of a thatched roof sitting on the pavement, with no sign between roof and floor of the two-storey cottage that had turned back into mud between its two "waterproof" skins).
Dry a bit, dry a bit more, add lime coats inside and out, and relax.

 

[biffvernon]

Matt, those numbers 35 and 55 just seemed a bit low. Museums are typically air conditioned to an RH of 50-55%. I would have expected air in a domestic cob wall to be higher. The pretty but probably not very accurate humidity meter in front of me is reading 70%.

 

[Mike6]

The contractor you mention may be required to provide a drying certificate to satisfy the insurance company and to allow repairs to be approved.They have problems with older properties as they often have a 'bit of damp' which will not dry out .The contractor has no way of knowing what the moisture level was before the flood,so may be aiming for an impossible figure.The probes you mention may be 'deep wall probes' for an electronic moisture meter not a hygrometer.35-55 or so can be meaningless unless a profile up the wall is made as suggested before.Using an hygrometer may be more useful,flooring contractors worry about anything over 75%RH.Having said all that no one knows the state of the walls originally,if it looks dry,it probably is and you can tell the loss adjusters and/or the drying contractors that you are happy and to cough up for the right sort of repair.