Damp Proofing Result

[Ed_Zep]

And yes, the damp seems worse just above the skirting board.

Stuart Noble wrote:

[Stuart Noble]

If the damp is above the tiled bits that you assume are solid, I would guess there is no dpc under the concrete (usual in older houses). If the floor was latex screeded before the tiles went down, the water could be soaking up into the wall as the only means of escape. If this is the case then your dpc injection should stop it. If not get the firm back to re-inject. Maybe it will dry out in a month or so. It should at least be improving by now. Try drawing round the damp patches with a pencil and see if they're shrinking day by day. Are the floor tiles dry at the edges? If this was winter I might be testing for condensation by now but I just can't see the surfaces being cool enough in the middle of a hot summer

[meow2222]

it will be, as the bottom of the wall is in contact with the colder wet/damp ground, plus the underfloor void in the case of suspended floors, and being the coldest bit of wall condensation will happen there first. If youve got condensing your RH is too high.

NT

[Ed_Zep]

The tiles seem dry all over. Have taken your advice and drawn a line around the patch. I guess the real test will be in winter.

[Stuart Noble]

It's a tough one this, but you can probably achieve more by observation and a bit of logic than some builder coming in cold and hazarding a guess. The fact that it's an internal wall rules out a lot of the potential causes

[meow2222]

yes, leaving only 2 likely options.

NT

[Ed_Zep]

Leaking pipe or real rising damp?

[e-mail] wrote:

[meow2222]

leaking pipe or condensation, rising damp is highly unlikely.

NT

[Fitz]

It's very obvious that a lot of people are sceptical about rising damp and chemical DPC to the point that they are suggesting gross incompetence and/or fraudulent activity on behlaf of the companies offering this service.

So I have a couple of questions:

1) Is the actual method of injecting a chemical DPC flawed for designed purpose? i.e. in controlled conditions where you can create an environment in which rising damp is manifested is it physically possible to stop it by injecting the wall? 2) Has anyone been persued, investigated or prosecuted for offering fraudulent services with regard to injecting chemical DPC? If not whay not, given peoples insistence of the level of con going on?

I've seen damp come up through a floor without a DPC but don't think I've ever seen proper rising damp in brick work, but then my experience in this matter is limited.

[meow2222]

You need to take one step back here, as experiments to produce rising damp have repeatedly failed.

There are 2 answers here. The first is the case of a company that was injecting water into brickwork instead of dampproofing chemicals. They did this for an extended period, treating hundreds of properties, and never had any complaints as a result. What one can conclude from this is that dpc injection has very little or no effect in curing cases of damp walls.

The 2nd answer is there are numerous companies in many areas in most market sectors that routinely offer cures that dont cure anything other than their own shortage of income. If they can construct and maintain an argument to bolster their claims, regardless of whether its flawed, its not technically fraud in the eyes of the law, and they can and usually do continue trading.

It will if the floor is in the wet ground, but that in itself is not rising damp.

NT

[Andrew Gabriel]

This comes from research by BRE to demonstrate rising damp sufficient to cause any problems is extremely unlikely, and a number of the firms being caught injecting water or some other useless solvent under the guise of injecting a damp course.

A properly injected chemical DPC will create a moisture barrier. It works by coating the internal surfaces in the brickwork with a water repellant, so they cannot draw water up by capilarity. It won't stop water coming through if there's any pressure behind it (i.e. can't be used for tanking). If the damp was wrongly diagnosed, the chemical DPC may well just move the damp somewhere else (such as above the DPC).

The work is usally accompanied by other things such as reducing ground level, replastering, etc, and these probably will make a difference.

[Stuart Noble]

Condensation in a heat wave?

[meow2222]

yes. I suppose you want an explanation. It is temp difference that causes condensation, not absolute temp (assuming we're talking above freezing). On a hot day the air can hold a lot of water vapour (the hotter the air, the more water vapour it can carry). If the hot air has highish RH, and meets a cold wall on wet ground, the 20C drop can cause condensation. Although summer condensation is less common than in winter, it does occur.

NT

[Stuart Noble]

Oh yes please, headmaster.

It is temp difference that

I'm perfectly well aware of how condensation occurs thank you, but I've never seen it during a hot summer, and I doubt you have either.

[Dave Fawthrop]

|It is temp difference that |> causes condensation, not absolute temp (assuming we're talking above |> freezing). On a hot day the air can hold a lot of water vapour (the |> hotter the air, the more water vapour it can carry). If the hot air has |> highish RH, and meets a cold wall on wet ground, the 20C drop can cause |> condensation. Although summer condensation is less common than in |> winter, it does occur. | | |I'm perfectly well aware of how condensation occurs thank you, but I've |never seen it during a hot summer, and I doubt you have either.

The temperature of *dry* *internal* walls will approximate to the average air temperature. (average over several days and both sides of a wall) In a hot summer temperatures, this average temperature will be high.

I did some experiments and wrote a simulation of temperatures in masonry walls, subject to air temperature changes, many years ago, but I can no longer run the code.

As digital probe thermometers are now quite cheap, and available. It might be a good idea to drill holes in the damp wall and measure the temperature, at various depths. I will have to think about the effects of dampness.

[Stuart Noble]

As masonry retains heat, I can't see where this 20C difference in temperature the honourable gentleman refers to is going to occur. A damp wall would be colder, but the source of the damp would not then be condensation. What was the purpose of your research out of interest?

[Dave Fawthrop]

On Thu, 10 Aug 2006 09:29:53 GMT, Stuart Noble wrote:

|Dave Fawthrop wrote: |> On Thu, 10 Aug 2006 07:37:09 GMT, Stuart Noble |> wrote: |> |> | [e-mail] wrote: |> |> |> |It is temp difference that |> |> causes condensation, not absolute temp (assuming we're talking above |> |> freezing). On a hot day the air can hold a lot of water vapour (the |> |> hotter the air, the more water vapour it can carry). If the hot air has |> |> highish RH, and meets a cold wall on wet ground, the 20C drop can cause |> |> condensation. Although summer condensation is less common than in |> |> winter, it does occur. |> | |> | |> |I'm perfectly well aware of how condensation occurs thank you, but I've |> |never seen it during a hot summer, and I doubt you have either. |> |> The temperature of *dry* *internal* walls will approximate to the average |> air temperature. (average over several days and both sides of a wall) In a |> hot summer temperatures, this average temperature will be high. |> |> I did some experiments and wrote a simulation of temperatures in masonry |> walls, subject to air temperature changes, many years ago, but I can no |> longer run the code. |> |> As digital probe thermometers are now quite cheap, and available. It |> might be a good idea to drill holes in the damp wall and measure the |> temperature, at various depths. I will have to think about the effects of |> dampness. |> | |As masonry retains heat, I can't see where this 20C difference in |temperature the honourable gentleman refers to is going to occur. A damp |wall would be colder, but the source of the damp would not then be |condensation.

I would agree. I could probably sort something out if I knew the, time of day, air temperature, and the temperature at various depths in the wall.

|What was the purpose of your research out of interest?

Curiosity, and practicing programming, c1978, I had access to a computer PDP11 03, because of my work. My job spec said that I could program computers, which I could not do, and I chose to learn in my own dinner times.

[manatbandq]

Every day, when I have a shower.

MBQ

[meow2222]

This is true upto a point. But what... underground earth temps are well below outdoor summer temps, and the base of a wall in a cellar will be well below outdoor temp. The whole cellar will be below outdoor temp, and the bsae of the wall, which is in thermal contact with wet earth, will be cooler still.

Now add the wide variatoins in outdoor temp over the 24 hr cycle and you'll sometimes get a wide temp diff between cellar wall base and outdoors.

I guess you upgraded from that PDP11!

NT

[Stuart Noble]

I didn't think we were talking about people living underground