Acceptable dampness in walls?

[Jack07]

Hello,

Ive think ive rectified a few problems in my house that have caused damp problems.

Ive gone and bought myself a damp detector with a digital display. So now im probably going to be completely obsessive and spike my walls everywhere!!

I would just like to know what an acceptable level of damp in a wall is?

At the moment the downstairs low don is about 3% with the ceiling level being about 1% and upstairs about 8-10% low with about 19-20% high up the wall.

Ive only been in a fortnight so the readings will slowly come down ( I hope)

Thanks again,
Jack

 

[^woody^]

Wall moisture content can vary over a day or seasonally - anything from 0-20% and it will vary by location too

Damp meters are not designed for walls or ceilings, and give incorrect readings in anything except bare untreated timber - and you are only measuring surface condensation moisture which is normal and a bit meaningless.

Throw it in the bin

 

[Jack07]

I didnt purchase the meter to monitor the wall dampness closely but just to give me an idea to whether the walls are drying out or maintaining their dampness.

It is quite inmportant to me to identify which areas need attention.

 

[tim00]

1. what woody has told you is quite right - swerve away from self diagnosis with a MM.

2. why dont you say what remedial measures you have taken and what obvious signs of "damp" remain where?

 

[foxhole]

I didnt purchase the meter to monitor the wall dampness closely but just to give me an idea to whether the walls are drying out or maintaining their dampness.

It is quite important to me to identify which areas need attention.

The meter will not do this, as stated not intended for walls.
Moisture at surface will vary hour by hour, day by day depending on many factors.

 

[Perry525]

Nevertheless, it will indicate if the wall is dry!

I recommend that you keep your heating on at a steady temperature for a least three days, preferably a week. Then take a careful look at each wall to see if there are any damp patches.

You may expect to find rising damp in any wall up to four feet from the ground outside (look outside to make sure nothing is bridging the damp proof course and that the ground is at least six inches below the dpc. (more is better)
Damp will appear anywhere, if the wall is exposed to driving rain, ditto leaking gutters or down pipes or water pipes or leaking central heating.

Damp can also appear if you have ventilated cavity walls that are below the dew point, ditto chimneys which are often the second coldest spot in a room.

 

[masona]

Jack07, worth a read > http://www.askjeff.co.uk/rising_damp.html

 

[Jack07]

1. what woody has told you is quite right - swerve away from self diagnosis with a MM.

2. why dont you say what remedial measures you have taken and what obvious signs of "damp" remain where?

A couple of ridge tiles had cracked on my hip end and water was running down tmbers and onto disused chimney. Black mold and severe dampness were obvious to about 1/3 way down breast.

I have now repaired tile and it feels drier but a bit of staining remains. this was a fortnight ago and I tested it with the meter yesterday. Up to the damp 'tide' mark is reading 2-4% and above tide mark is 20-36%.

Will give it a few more weeks to dry out as water heating tank is situated next to chimney breast.

Signs of rising damp as reading low down are always greater that higher up walls on ground floor.

 

[^woody^]

Once plaster has got wet, salts are brought to the surface which then cause the meter to give artificially high readings

The key to using a meter is not the readings, but the interpretation - and that won't be in the instructions

 

[Jack07]

Once plaster has got wet, salts are brought to the surface which then cause the meter to give artificially high readings

The key to using a meter is not the readings, but the interpretation - and that won't be in the instructions

Ive been reading up on those 'hydro' salts. My chimney breasts have wooden battens as angle beads, its a 1930's house. The readings in these are very low compared to the plaster which as you suggest probably contain all the salts.

Thanks for the advice,
Jack

 

[tim00]

What Woody says is spot on. Interpretation being the key to moisture meter use.
There is no acceptable level of damp in plaster if you can see it or feel it with the back of your hand

In your case, as Perry said, give it more time to dry out - keep the room on low heating and maintain ventilation. No decorating. Am i right in thinking that your difficulties are in a bedroom, no ground floor involvement?

Be alert to that Feed & Expansion tank in the loft ( esp. if it's galvanised) for leaks.

You apparently dont have felt under your roofing material - something for the great, eventually to-do list.

 

[Jack07]

What Woody says is spot on. Interpretation being the key to moisture meter use.
There is no acceptable level of damp in plaster if you can see it or feel it with the back of your hand

In your case, as Perry said, give it more time to dry out - keep the room on low heating and maintain ventilation. No decorating. Am i right in thinking that your difficulties are in a bedroom, no ground floor involvement?

Be alert to that Feed & Expansion tank in the loft ( esp. if it's galvanised) for leaks.

You apparently dont have felt under your roofing material - something for the great, eventually to-do list.

After the new year our plans are going in for a 2 storey extension that will be adjacent to the problem room. Yes, it is an upstairs bedroom, the expansion tank is plastic and no sign of leaks.

So roof will be getting replaced. Hoping the original welsh slate can be saved and reused. might save me a few bob.

 

[tim00]

Be determined to save all the welsh slate thats not already damaged. By slow and steady lifting and nail pulling, it's common to preserve most in-situ slate. Be on site and dont allow hurried and careless ripping up and throwing about.

Each slate should be grasped by the tail, lifted slightly and then de-nailed with a nail puller or hammer claws. Roof ladders to be used until safe footing on the battens is revealed.

Slate,esp. Welsh slate, is expensive and i've seen roofers cause hundreds of pounds of extra slate costs by sheer carelessness.

 

[Jack07]

Be determined to save all the welsh slate thats not already damaged. By slow and steady lifting and nail pulling, it's common to preserve most in-situ slate. Be on site and dont allow hurried and careless ripping up and throwing about.

Each slate should be grasped by the tail, lifted slightly and then de-nailed with a nail puller or hammer claws. Roof ladders to be used until safe footing on the battens is revealed.

Slate,esp. Welsh slate, is expensive and i've seen roofers cause hundreds of pounds of extra slate costs by sheer carelessness.

Thanks for advice, already had a few roofers around to give quotes. One stated that he would be aiming to save around 40% of the slates!

Didnt really like the response so called a few more and they said they could save all. Happy days. But I will still make sure I stand over them like a hawk ( or is that under them?)

thanks again.