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    • CommentAuthorSpaceTofu
    • CommentTimeAug 16th 2017
    Hi all,

    we have a period terraced house, with extension at the back, double glazing. Overall pretty well doing in terms of condensation / damp.

    However, I noticed the other day that the 3 or 4 1kg pack of salts (yes, I know. I love bulk saving offers) have absorbed LOADS of humidity. They are stored in cupboards that are well above 1.50m height from the floor. Further, the external wall on the back is south facing, although it doesn't see much direct sunlight due to the extension of the next door neighbour.
    When we cook we always turn on the fan and we do not believe there is any broken pipe in the vicinity. The back of the cupboard looks alright and not rot, if a pipe would have burst I would have expected to see rotting wood.

    I do want to warn at this point that when we were still house hunting and having developed a penchant for period houses, I did back then a lot of reading into rising damps, the myths and the facts.
    I am therefore a "rising damp" skeptical, although I do recognise that with certain materials / constructions it can actually happen.

    The kitchen is in the rear extension bit and is actually sitting on a floor of solid concrete (the "main" building is sitting on raised wooden floors).
    The kitchen did have some rising damp interventions a good five years ago, as we came to know when purchasing the property.
    The report mentioned things like "Conductivity meter tests gave patterns normally associated with rising damp (sharp cut-off) in those ground floor walls shown in the attached plan; this is probably due to the lack of an effective DPC " and "the plaster on the walls marked in the plan looks significantly decayed . This condition is likely to be a product of residual salt, which might be hygroscopic"
    The work ultimately carried out was "to drill and inject a chemical DPC, hack off and re-plaster as above specification (plaster will be hacked off to a min height of 1 metre and replaced to our spec in the area marked in the plan. Sand and cement with ratio 3:1 will be used and incorporating a waterproof/salt inhibitor in the gauging solution)"

    My questions now are:
    - with the (little) details provided, do you think I am witnessing actual rising damp?
    - if the above is true, leaving aside poor workmanship, how is it possible that after solely 5 years of that chemical DPC carried out we are witnessing rising damp?
    - I was reading back in the days that once can purchase "salt tester" (I do not remember the correct name) and other cool gadgets to DIY check for rising damp. Are those readings actually relatively easy to carry out and interpret for a novice?
    - last but not least. Do you know any good damp expert, i.e. that does recognise that rising damp exists but only in 5% of the houses? We live in the Bristol area

      kitchen DPC.jpg
    • CommentAuthortony
    • CommentTimeAug 16th 2017
    1 no!
    2 unlikely
    3 probably a carbide tester
    4 I give talks about damp mould and condensation and have a good understanding of the problems encountered, damp salt in a cupboard cannot be used to diagnose rising damp.

    I am willing to test a few samples from your walls, all you have to do is drill a hole like for fixing something 75mm deep into the wall, carefully collect the dust on a sheet of paper, immediately shoot it onto a piece of kitchen foil, then into a small resealable poly bag with a sample number on it and send it all to me in the post. I will weigh the sample, dry it in a warm oven, reweigh it and calculate the percentage moisture. I suggest several samples, two just above skirting height, one at a meter up, one in the wall behind the cupboard if you can, one in a wall of the main house. no more than six please.

    the last time I did this in a so called damp wall that needed 8k spent on it the samples were all bone dry (between 1 and 2%) the surveyors moisture meter was flashing red. and on the party wall which didn't have any problems it was 2.1 to 2.4% higher but still below the level to worry about.

    Please stick a fiver in the envelope and I will post results on here for all to see.
    • CommentTimeAug 16th 2017
    Salt is hygroscopic; it absorbs damp from the atmosphere. So it seems to me more likely that it has done that than absorbed it from the wall. What is the humidity in the kitchen and in the cupboard in particular?

    What Tony suggests sounds sensible as a means to put your mind at rest.
    Posted By: djhWhat Tony suggests sounds sensible as a means to put your mind at rest.

    Especially as he is suggesting you send it in a (non)hermetically sealed bag through a postal system and environmental circumstance over which no one has any control to do a test that will involve a difference of micrograms. But its value will be to put your mind at rest:smile:

    What djh said about salt being hygroscopic +1
    • CommentAuthorSpaceTofu
    • CommentTimeSep 1st 2017
    Sorry for the very belated reply, juggling between work, long weekends away and house chores doesn't leave me with too much time to sit in front of the PC.

    tony, I really appreciate your inputs.
    I also like the idea of having some samples tested, but the points raised by Peter_in_hungary are making me perplexed about the reliability of the results?

    True, salt is hygroscopic, it absorbs water.
    I am simply wondering where the hell is all this humidity coming from seeing that we tend to have a proper anti-condensation behaviour (i.e., fan on and window open when cooking, opening the windows a bit everyday, if weather allows it).

    I am fearing it is maybe the cold, non raised concrete floor but I am then wondering why it shows up into the upper cabinets?

    I have done some "testings" (quite an overstatement).

    On day 1 I measured the humidity in the upper cabinets (closed): 70/74% H, as opposed to 61% over the kitchen top.

    On day 2 I measured the floor 79% H.; the lower cabinets, closed, 83/84%
    On the working top, the H was dropping to 74%.

    Also, seemingly leaving the window half-shut throughout the night results in lower H level in the kitchen in the morning, but it's also cold.

    Essentially, I am afflicted by two problems: problem A is damp cabinets, it is not rising damp, agreed on that, then what it is? Simply the accumulation of humidity in a close, small environment (cabinet) which is located in an already quite humid environment (kitchen).
    Problem B is a kitchen which is quite humid. I believe if I were to sort out problem B, problem A would therefore sort itself out? :cry:
    • CommentTimeSep 1st 2017
    What is/was the outdoor relative humidity (RH) at the time of your cupboard etc readings? In unheated weather, you can't get internal RH lower than external - it's essentially the same air, exchanged through open windows etc. And in these 'shoulder' seasons, external RH is generally high.
    • CommentAuthortony
    • CommentTimeSep 1st 2017
    Interesting and horrid things happen in all cupboards on outside walls. They effectively insulate the wall from the heat in the room making them colder than the rest of the room. Unfortunately condensation is looking for places like that to its thing.

    Try taking off the doors or leaving them open.

    To some extent the same is true of the kitchen and its relationship with the house. It is kind of acting as a dehumidifier.

    Happy to do samples, wrapped in foil in sealed poly bags, the ones with zips on them.

    I am expecting dry inside the walls :)
    • CommentAuthorSpaceTofu
    • CommentTimeSep 2nd 2017
    Fostertom, I referred to the H surveys I carried out as [quote]"testings" (quite an overstatement).[/quotes]

    I am aware the outside H plays a major role, I was really after some quick&dirty measurements to compare the inside of the cabinets to the general kitchen environment. Measurements were carried out in an hour time span, so I assume the potential change of external H couldn't have been so dramatic.

    Tony, interesting point about the cabinets on the outside wall. Even more interesting though, one of the lower cabinet that I measured (H of 83/84%) is actually located against an internal wall, the other one against an outside wall; said this, they both shared similar humidity (83% and 84%!!)

    taking off the doors / leaving them open is not really an option! :wink:

    When you are saying that the kitchen acts as a dehumidifier for the house, meaning that it kind of sucks the humidity from the house to retain it within its four walls? Interesting point.

    If the offer for the samples still stand in some weeks time, I'll contact you again, right now we are in a quite couple of hectic weeks.

    Is the thought of "raising" the floor and actually creating a void (to either be left void or filled with some fantastic man-made magic materials) something that could help allievate the problem? The dining and front room are after all on raised "victorian" floors and aren't as damp and cold as the kitchen.
    We are anyway considering a kitchen re-haul, so better thinking now of raising floors than when it is going to be too late!
    • CommentAuthortony
    • CommentTimeSep 2nd 2017
    I am up for samples when you are ready, no need for the fiver now either.
    • CommentTimeSep 2nd 2017
    Posted By: SpaceTofusucks the humidity from the house to retain it within its four walls?
    not 'to retain it within its walls', but to condense it out on its cold wall surfaces. Same happens with cold window surfaces.

    With that going on, the removal of water from vapour (to liquid) leaves a kind of local vacuum of water vapour, which is filled by surrounding water vapour migrating through the air (i.e not by bulk air movement) - hence 'sucks humidity from the house'.
    • CommentAuthormark_s
    • CommentTimeSep 4th 2017
    What about the obvious questions?

    Construction of the walls? insulation? roof? gutters etc?
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