We’ve had our hall radiator off for a few months (since spring actually… ) to be replastered, new floor etc. I have just felt the lower part of the wall, on the inside and it’s wet. Is this just condensation, from it being cold outside the last few days?

I’ve never noticed it before but it has been warm, and we’ve had bits stored in there too, so I doubt I’d of noticed it anyway.

There’s no broken gutters above it. We replaced the floor itself in the hall with 1 inch thick ply, and there is a slight gap around the edge, not sure if that could be a factor? Or the fact all the radiators have been on in the house the last few days apart from the hallway

Should I be concerned?

Hi Mr Blond!. Not enough information there. I built an eighty square metre extension in 2015, and the floor has four inches of polystyrene under six inches of concrete, the DPC is under the lot. Walls have a DPC jointed to the floor DPC two brick courses under the floor level. Have a look at whether you have DPC's, and at what level. Also make sure the walls are fully dried out, (three months), and you have no water leaks from pipes or radiators. Hope that helps.

Is the ground level outside higher than the inside? Is it a cavity wall or solid?

Jim

Dampness in any building is one of three things.

1 Direct damp from outside or components - broken storm water pipes or gutters, missing sealants around openings, broken services such as water pipes or internal plumbing, broken or missing roof coverings etc.
2. Rising damp from the ground - bridged DPC's, normally ground levels too high, punctured floor membranes, incorrect damp-proving works
3. Condensation. - internal warm moisture laden air meeting a cold ininternal face such as window or cold spot in external walls. Often cured by adequate ventilation

If you have had the rad off for sometime I would be looking at (2) above to start with especially if you have been working in the floor. Has new plaster bridged or damaged any DPC . There is a big difference between wet and damp. Many of my clients paint a really bad picture over the phone but when I get on site its just a bit of surface dampness due to condensation. You said you have replaced the floor - to me that means digging up everything down to reduced earth level and starting again but do you just mean replaced the floor covering? Is it a timber floor or solid concrete floor or even quarry tiles laid on ash?
Is the damp patchy, low level, high level, widespread or just where the rad was once fitted?
You might need to investigate further to get more causes rather than just looking at symptoms. 405 AB exec seats Baltic and Cirrus
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Interior wall or exterior ?

How old is the house ?

I have an old house no cavity's and the joints are all lime mortar so its breathing lol
Buy a portable humidifier it will assist in drying out

But has the DPC been bridged? 2018 SE SDV8 4.4 Byron Blue

Photos may or may not help .
One things for sure , plaster can take a long time to dry especially in colder months especially if it’s a thick coat , good ventilation helps immensely with gentle heating .
The lower levels of plaster will take longest to dry with colder air at lower levels and the water content of the new plaster always sinks to the lower levels by gravity .
As Kot mentioned , a dehumidifier will help dry the air and the plaster .
Best move all the stored items away and give the wall some breathing space .

Damp coming through is likley to cause severe staining as it takes an age to coe through and brings with it all the colouration of sand plaster etc... If its simply like teh wall has been splashed its most likley condensation.

A Simple crude test to determine if moisture is coming through the wall or landing and condensing on it is to dry an area as much as possible use dehumidifiers and heaters and ventilation so its dry to touch.

Then tape a large bit of foil ie A4 size on the wall with all edges sealed then the next day remove if its wet on the inside then its most likely a damp wall if there is condensation on the outside of the foil then its condensation. i used this to covince a tenant that her drying washing and not opening windows was causing mould rather than a leak from my flat above!

Not the most scientific test but gives a good indication.

Failing that a moisture meter ie damp meter will determin whats going on beneath the painted surface of the wall.

Late reply one and all, apologies but have been working away since before Christmas

I sealed the small gap around the new plywood floor and used a dehumidifier and the wall is no longer wet, so I’m guessing it was just cold air from the void under the floor that caused the wet (to the touch) wall.


But, on a different wall, in the hallway where the stairs start, the corner of the house, on the newly plastered and painted wall there’s a small black patch coming through, right in the corner. It’s only in one spot, the coldest corner of the stairwell.

It’s about 1m up from the ground level, so doubt it’s rising damp? Could it be because there’s no heat in the hallway and stairwell and it’s the coldest part of the house?

Yep, I think you probably have it spot on there. It’s amazing how much damp will occur in unheated recently renovated rooms. At a metre up it’s unlikely to be rising damp. That would usually start at the bottom. If it’s an external wall it could be penetrating damp, but again that’s fairly easy to rectify by seeing if there is an obvious pointing defect on the other side….

But I’d go with condensation 👍🏻 There is nothing that can't be fixed with a hammer😜😜
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Put the dehumidifier next to it, you dont want the damp patch to grow mould as the spores can be breathed in and not very good for you.
Look on the other side of that wall is it outside? is there guttering leaking etc etc could be penetrating damp how is the pointing etc etc if its internal is there any pipes sinks showers etc on the other side of the wall? 2018 SE SDV8 4.4 Byron Blue

Morning guys (rather s3xist assumption I know)

Sorry I should of said, yes it’s an external wall, corner of the house. 1930’s so it’s all solid brick. I’m certain no issues with the pointing and I sealed it last summer with a clear brick sealant as it’s the exposed corner of the house when it rains

1930's house! with solid walls and no cavity, you need to check what mortor is used on the building of the house.

If its Lime based, then you should not use sealant on the external wall as the lime mortor needs to breathe and any damp in the wall actually evaporates out via the `Lime mortor and brickwork etc. Also your internal plaster on this wall will also be lime based so any trapped damp will now migrate through your plaster showing as dark patches etc
as it cant breathe through the bricks and mortor to the outside anymore.

If its cement based mortor then you are ok to use sealant.

However as you have used sealant, any damp is now stuck in the solid brickwork
Being a solid brick wall it takes a long time to draw that damp out, once you have removed all potential damp causes (blocked guttering etc leaves etc) heat the room and use a dehumidifier.

A dehumidifier works slower in un heated environment, the warmer the surrounding air the more the air can hold extra water vapour- the faster the dehumidifier can then reclaim that water. The faster the damp can be removed. 2018 SE SDV8 4.4 Byron Blue

Thanks Kot - interesting point. I'm assuming its normal cement, is there any way of telling?

I know a lot of very old places had horse hair and lime plastering, but didnt know about the cement too? Currently chipping off a load of loose plaster in hallway, what would i look for to see if its normal plaster or hair/lime?

If the plaster is pink, then it's not correct. We used to own a house many years ago which had been refurbished. Unfortunately they used standard Carlite? plaster on the lower half of the walls. When we sold the surveyor raised a damp issue that was caused by them using the wrong type of plaster to repair the walls with. Basically it never dried out.

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