Should I worry about damp that isn't causing problems.

tomh · 20 Oct 2008

Hi,

I was recently replacing a cracked mains socket in my flat. When I removed the socket face plate I noticed that metal back-box was rusted, so I figured I better replace that too. After removing the old back-box I tested the wall behind it with a damp meter, and it came up as damp.

Now, I've never noticed any obvious signs of damp on that wall (no mold, or discoloration, or anything like that). So its not causing any visible problems.

But is this something I need to worry about (can damp in a wall cause structural or other problems with the wall?), or can I just replace the socket and take the attitude of "out of sight, out of mind"

cheers
--
tom

JohnD · 20 Oct 2008

tell us about the wall

interior? exterior? next to the bathroom or sink? water main in the floor under it? shower or radiator on the other side (=plumbing leak)? drainpipe on the other side? Five-hundred-year old cottage? basement flat? Is there an overflow pipe above?

Do you have a badly-trained dog or small boy?

those metal back-boxes are galvanised steel and take a long time to go rusty.

tomh · 20 Oct 2008

JohnD said:
tell us about the wall

interior? exterior? next to the bathroom or sink? water main in the floor under it? shower or radiator on the other side (=plumbing leak)? drainpipe on the other side? Five-hundred-year old cottage? basement flat? Is there an overflow pipe above?

Do you have a badly-trained dog or small boy?

those metal back-boxes are galvanised steel and take a long time to go rusty.

Sorry should have given abit more info.

Its a first floor flat (large Victorian house converted to flats in the 80's). Externally the wall is rendered so its difficult to see the state of the brickwork, but there is no obvious place for water to get in, and no signs of water damage to the external render.

The wall/room in question is actually an extension to the original building that was built at the time it was converted to flats.

I'm 99% percent certain there are no water pipes nearby, as radiator is over the other side of the room, and there are no sinks or showers in the room or anywhere nearby.

No small dogs or little boys!

Testing the wall with a damp meter shows no damp in the plaster, I only detected damp in the wall itself behind the back-box.

With the socket in place there are no signs of damp at all, so I could ignore the problem, but I don't want to be storing up bigger problems for later...

cheers

JohnD · 20 Oct 2008

go outside when it's raining and look for dripping gutters.

test your meter on a brick you consider to be fairly dry.

try to work out if there could be a shower or something by the wall in the room above.

if there is a roof above it might be leaking onto the wall.

tomh · 20 Oct 2008

JohnD said:
go outside when it's raining and look for dripping gutters.

test your meter on a brick you consider to be fairly dry.

try to work out if there could be a shower or something by the wall in the room above.

if there is a roof above it might be leaking onto the wall.

Ok, that sounds like good advice. I know the guy who lives above and his room is the same layout as mine, ie no pipes near that wall. However he does get condensation in his room.

If left unchecked, is damp in a wall likely to cause problems in the long term?

ie do I need to sort this out, or could I leave it be?

Cheers
--
tom

JohnD · 20 Oct 2008

damp will spoil decorations, can perish plaster, and, worst of all, can cause timber to rot.

If the wall is wet you should look for it affecting the ends of the joists (probably built into the brickwork) and the skirting board where it is in contact with the wall. With a bit of practice you can smell damp plaster and damp wood.

If the wall is a modern one it will have a cavity, and the inside should not ever get damp. Howevere it is possible for water to run down inside a cavity, usually from a roof or pipe leak, and it is possible for water to bridge across from the outside leaf if there are lumps of mortar caught on the wall ties.

Or it might be your meter is inaccurate, but if the electrical wall box has gone rusty, there must be damp.

^woody^ · 20 Oct 2008

You need to distinguish between dampness and normal moisture content of the brick/wall.

Poking any damp meter in it will give a reading of some sort.

Old socket boxes can rust, walls can retain some moisture. Its natural

Its only a problem if it affects your use of the room.

In any case, as its a flat it is not your problem - its the responsibility of the landlord

tomh · 21 Oct 2008

JohnD said:
damp will spoil decorations, can perish plaster, and, worst of all, can cause timber to rot.

If the wall is wet you should look for it affecting the ends of the joists (probably built into the brickwork) and the skirting board where it is in contact with the wall. With a bit of practice you can smell damp plaster and damp wood.

If the wall is a modern one it will have a cavity, and the inside should not ever get damp. Howevere it is possible for water to run down inside a cavity, usually from a roof or pipe leak, and it is possible for water to bridge across from the outside leaf if there are lumps of mortar caught on the wall ties.

Or it might be your meter is inaccurate, but if the electrical wall box has gone rusty, there must be damp.

Cheers John, sounds like it worth me getting to the bottom of it. I presume rotting joists is a worse case scenario, but it doesn't sound good!

I guess I need to check my meter again a brick wall that I know is ok.

^woody^ said:
You need to distinguish between dampness and normal moisture content of the brick/wall.

Poking any damp meter in it will give a reading of some sort.

Old socket boxes can rust, walls can retain some moisture. Its natural

Its only a problem if it affects your use of the room.

In any case, as its a flat it is not your problem - its the responsibility of the landlord

Thanks Woody, it is a flat, but I own rather than rent. So it is my problem

^woody^ · 21 Oct 2008

You may own, but you are not normally responsible for the structure - the building owner/landlord/service agent is

foxhole · 24 Oct 2008

What damp meter did you use, on for timber? would give useless results.

PerryOne · 24 Oct 2008

It is possible that its an old box that has been reused.
When you write that there is damp as per a damp meter, what % of damp is there?
All walls are damp to a degree and usually it does no harm, however where damp comes into contact with wood, paper, leather etc these things will soon be covered in mould, which isn't nice.
As far as joists are concerned the lay of the floor boards will answer that.

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Should I worry about damp that isn't causing problems.

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