damp issue and how to use a moisture metre

[donmaico]

I have had a major damp issue with a south facing wall for some time.In order to tackle the problem in the past year I had new window trays fitted , repointed and repainted the brick the wall , had the roof verge tiles properly edged so no holes are left , then I repointed and painted the area below the felt DPC using bituminous paint, leaving a 9" inch gravel edge alongside the base of the wall .I also checked the guttering and that is fine.
There is still a problem,though, because i am having to empty a dehumidifier daily.
Anyway I bought one of those cheap damp metres but cant figure out what the percent readings I get refer to. From the skirting board up to about 2 ft I get a 35% reading ins one areas , but further up the wall its almost zero.

As it can only go one way i.e. in, maybe I am being a bit impatient and whatever moisture is in the wall is taking its time to come out via humidifier. Can someone please advise me? Thanks

 

[AronSearle]

There is still a problem,though, because i am having to empty a dehumidifier daily.

Are there visible signs of damp?

The fact that you are emptying the dehumidifer, means that you are emptying the dehumidifiyer, it will always be able to keep drawing out moisture. What humidity is it set to, and does it ever reach this and turn off?

Moistre meters in walls are terribly unreliable, they work by electrical conductivity which will be affected by all sorts of factors. Walls that have been moist may have been treated, and these may affect readings.

With the work done, was an actual water ingress issue detected, or was it assumed and various measures taken?

 

[donmaico]

on the underside of the top of the window recesses just below the new concrete lintels we had fitted there was a considerable amount of mould present .I killed that off with bleach but it has left the plaster stained on the side of the window there is also evidence of water ingress because the pain has peeled .Those areas appear to be dry now indicating that the old water trays had failed and needed replacing.
Its the area above the skirting board , each side of a central window that had once been a door that alarmed me recently the paint had peeled off there as well.I say door because there is a course of stretcher bricks jutting out ,above the window and going right down each side of itt to a brick step
Its also adjacent to two radiators .
The humidifier is only a cheap one I bought that only has one setting and has cut out on a number of occasions although `i mostly empty it before to does that
The wall just feels somewhat damp around those areas i mentioned above after the last works I had carried out particularly behind the two radiators and near that central window.

 

[AronSearle]

Hmmm, sounds more like condensation.

Concrete lintels will be particularly prone to cold bridging, heaters will draw air upwards, and the areas either side of the heater may be cold. The areas you are getting damp are the areas that condensation typically happens.

Lowering humidity will help, what is concerning is that you are running a dehumidifyer and emptying it every day. Unless it is crap, or you have lot's of excess humidity, the problem might just be excessivly cold wall surfaces.

Those areas appear to be dry now indicating that the old water trays had failed and needed replacing.

It *could* be that the humidity is now low enough for condensation to not occur on those areas, but still on others, particularly at lower level as the warm air rises.

It's all guesswork on my part however, it would help greatly if the dehumifier hat a sensor, as that would help you measure the humidity level.

Does it have a manual that gives a cut out point, most of them will stop at 30% humdity.

 

[donmaico]

the concrete lintel only stretches along the exterior skin so i cant see how that would create a bridge
I doubt I still have the manual for the dehumidifier but I could always hire one with a sensor .What would a normal level of humidity considered to be?

if its just ammeter of condensation then surely i would need to do is one then fanlight windows slightly ?

 

[Flyboytim]

If your car windscreen mists up with condensation, you do not turn up your aircon to eco and max AC (equivalent to using a dehumidifier), you don't open the windows for ventilation either, especially on a wet day. It would take ages to demist the windows by those methods.

For best effect you blow air over the surfaces suffering from condensation or you heat the surfaces directly. Unless you have heating elements embedded in the walls, your choice is to blow air over the areas suffering from condensation using a fan of some sort.

You do not need additional heating, or to raise the thermostatted temperature of the central heating, which will increase the capacity of the air to contain water vapour, just increased air movement to speed evaporation and to equilibrate the wall temperature with that of the ambient air.

Remember that air stratifies in draught free rooms when there is no activity so the air that has cooled at the ceiling runs down the walls, and pools at lower levels. The only placed in a CH room where air rises is above the radiator and other heat sources.

Ventilate on cold, dry days only- the colder the day, the dryer the outside air - on wet or mild days, it will probably add moisture to the internal air, rather than remove it.

 

[AronSearle]

the concrete lintel only stretches along the exterior skin so i cant see how that would create a bridge

It likely does span the wall thickness, or has no insulation behind it and cold bridging occurs by another method, possibly a steel lintel for the inner leaf.

It doesn't prove it is condensation that it is the issue (though I think it likely), but there will be a cold bridge there.

Most older buildings with concrete lintels tend to have poor thermal design and are prone to condensation due to lots of cold walls.

What would a normal level of humidity considered to be?

30-55%

If you reach about 30-35% humidity, and still get condensation, then you really need to do something about the insulation in the building.

if its just ammeter of condensation then surely i would need to do is one then fanlight windows slightly ?

Yes opening the window will stop condensation, but so should a dehumidifier.

It would be really useful to know the humidity levels, as that will indicate if any of what I am saying is relevant, I only think it likely.

Can't you google the model number of the dehumidifier, it may not have settings but it should have a cut off point.

 

[GoodDIYjob]

Or buy a separate hygrometer if you really want to see what is happening to humidity levels?

 

[donmaico]

If your car windscreen mists up with condensation, you do not turn up your aircon to eco and max AC (equivalent to using a dehumidifier), you don't open the windows for ventilation either, especially on a wet day. It would take ages to demist the windows by those methods.

For best effect you blow air over the surfaces suffering from condensation or you heat the surfaces directly. Unless you have heating elements embedded in the walls, your choice is to blow air over the areas suffering from condensation using a fan of some sort.

You do not need additional heating, or to raise the thermostatted temperature of the central heating, which will increase the capacity of the air to contain water vapour, just increased air movement to speed evaporation and to equilibrate the wall temperature with that of the ambient air.

Remember that air stratifies in draught free rooms when there is no activity so the air that has cooled at the ceiling runs down the walls, and pools at lower levels. The only placed in a CH room where air rises is above the radiator and other heat sources.

Ventilate on cold, dry days only- the colder the day, the dryer the outside air - on wet or mild days, it will probably add moisture to the internal air, rather than remove it.

but surely the steam degenerated by heating the walls has to go somewhere? When I say open I meant small fraction MY fanlight has that capability.I can just open it a fraction and lock it therefore it acts like a trickle vent which I thought were for reducing condensation.
I'll buy a fan heater ,though, and direct right at the problem areas and see what happens

 

[donmaico]

the concrete lintel only stretches along the exterior skin so i cant see how that would create a bridge

It likely does span the wall thickness, or has no insulation behind it and cold bridging occurs by another method, possibly a steel lintel for the inner leaf.

It doesn't prove it is condensation that it is the issue (though I think it likely), but there will be a cold bridge there.

Most older buildings with concrete lintels tend to have poor thermal design and are prone to condensation due to lots of cold walls.

What would a normal level of humidity considered to be?

30-55%

If you reach about 30-35% humidity, and still get condensation, then you really need to do something about the insulation in the building.

if its just ammeter of condensation then surely i would need to do is one then fanlight windows slightly ?

Yes opening the window will stop condensation, but so should a dehumidifier.

It would be really useful to know the humidity levels, as that will indicate if any of what I am saying is relevant, I only think it likely.

Can't you google the model number of the dehumidifier, it may not have settings but it should have a cut off point.

we have got insulation the polystyrene bead variety which the council compelled to us to have done when w had our extension built .The inner lintel on two of the windows is actually made from oak as the house was built back in the 30s.Only the central window has an inner steel lintel but that one does not have a concrete exterior one because the existing stretcher bricks jutting out act as a lintel above the window. In any case the main ares of concern are at the bottom from the skirting to about 2 feet.
The humidifier is a Homebase MDT-10DMN3 Vallue 10 litre which apparent;y according to a Which report is slow at extracting water.This is the test result
Water extraction ability at 21°C 2 stars
Water extraction ability at 10°C 1 star
Noise 3 stars
Energy efficiency at 21°C 2 stars

this is the one http://www.homebase.co.uk/en/homebaseuk/homeware/dehumidifiers/dehumidifier---10l-211023

I am not at all sure what they mean by 10 LTrs. because the maximum amount a empty each day from the receptacle is about 1 ltr.

 

[AronSearle]

- the polystyrene bead - our extension built . In any case the main ares of concern are at the bottom from the skirting to about 2 feet.

So is this south facing wall part of the new extension, or old with new polystyrene insulation?

It's a little more suspicous if you are getting cold bridging/condensation on a new extension, if it is an old existing wall it is a little more reasonable.

Either way you need humidity readings or I could be talking a load of rubbish.

Going back to your original question, the best way to determine moisture contents is by oven dry testing (take a core, weight it, stick it in the oven and weight it again, the weight difference was moisture).

You still need atmospheric humidity readings, as measuring the wall tells you it is wet, not why.

I am not at all sure what they mean by 10 LTrs. because the maximum amount a empty each day from the receptacle is about 1 ltr.

10 Ltrs is how much it can suck out a day, assuming you attach a hose outlet or empty the tray 10 times a day.

Looks like a fan/refrigerator type dehumidifiyer with no humidity cut off.

You will need a hygometer then to measure humidity levels.

 

[jeds]

Forget the damp meter - too easy to get misleading results. Purchase some condensation indicator strips and some moisture pegs online. Fit them according to the instructions. When you have the result you will know if the wall is actually damp or just condensation. Also, a portable fan would be a better option than the dehumidifier. A cheap 12" or 16" fan running on low will cost next to nothing to run and will keep the air moving. Problem with dehumidifiers is they take moisture from anywhere and even in dry houses they draw moisture from somewhere. For all you know you could just be drawing it in from the kitchen and bathroom or even from outside.

 

[donmaico]

- the polystyrene bead - our extension built . In any case the main ares of concern are at the bottom from the skirting to about 2 feet.

So is this south facing wall part of the new extension, or old with new polystyrene insulation?

It's a little more suspicous if you are getting cold bridging/condensation on a new extension, if it is an old existing wall it is a little more reasonable.

Either way you need humidity readings or I could be talking a load of rubbish.

Going back to your original question, the best way to determine moisture contents is by oven dry testing (take a core, weight it, stick it in the oven and weight it again, the weight difference was moisture).

You still need atmospheric humidity readings, as measuring the wall tells you it is wet, not why.

I am not at all sure what they mean by 10 LTrs. because the maximum amount a empty each day from the receptacle is about 1 ltr.

10 Ltrs is how much it can suck out a day, assuming you attach a hose outlet or empty the tray 10 times a day.

Looks like a fan/refrigerator type dehumidifiyer with no humidity cut off.

You will need a hygrometer then to measure humidity levels.

Its in the old part , in fact it was there when we first bought the house 4 years ago as there were lumps of plaster hanging off the top part of two of the window recesses
I will order a Hygrometer but just been reading that the ideal humidity level is between 40-60% .Its handy to have one just to get some idea what it reads round different parts of the house

 

[donmaico]

Forget the damp meter - too easy to get misleading results. Purchase some condensation indicator strips and some moisture pegs online. Fit them according to the instructions. When you have the result you will know if the wall is actually damp or just condensation. Also, a portable fan would be a better option than the dehumidifier. A cheap 12" or 16" fan running on low will cost next to nothing to run and will keep the air moving. Problem with dehumidifiers is they take moisture from anywhere and even in dry houses they draw moisture from somewhere. For all you know you could just be drawing it in from the kitchen and bathroom or even from outside.

Condensation strips would appear to be a sensible first step and I have just ordered some.When you say fan do you mean a regular one or a fan heater?
I take your point re dehumidifier , the thought had occurred to me although I tend to keep the door shut when its on

 

[jeds]

Just a standard portable fan. You just want a slow trickle to keep the air gently moving.