Hello.
I have a 1940s house, so even though it has cavity walls (I'm still learning about all this) can cement rendering cause dampness on internal walls?
My kitchen and extension's external walls are rendering. One part is "hollow" though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.
Thank you.
Ed.
where is the dampness showing up?
ing about all this) can cement rendering cause dampness on internal walls?
low" though it was fixed and the dampness is more noticeable after rain. Al= so both rooms have a concrete floor.
If your walls are cavity, the only way damp can penetrate is if the cavity is bridged in some way (rubble/cement droppings etc.) ie some constructional defect Condensation is more likely.
Determining the source/cause of damp needs experience. More info/pix needed.
If you tap on rendering and it sounds hollow it is an indication that it has become detached/"unstuck" from the wall. However this in itself should not cause damp to penetrate a cavity wall. At some point it will fall off/get much worse & have to be fixed. Probably caused by frost action.
about all this) can cement rendering cause dampness on internal walls?
though it was fixed and the dampness is more noticeable after rain. Also both rooms have a concrete floor.
You don't say where the damp is. If it's at the bottom couple of feet of the wall I'd suspect that the damp proof course has been bridged on the outside by soil piling up or, in my case, by somebody plastering the inside wall all the way to the floor (and with the wrong kind of plaster too).
If it's higher than that is it the upper floor? If so suspect a roof or guttering leak or, as others have said, condensation caused by lack of ventilation.
We need more details.
Another Dave
No, damp is caused by water getting in, either by tracking across the cavity if it's been breached, or by a failed DPC
If it's 'hollow', it's not been fixed, otherwise it wouldn't be hollow.
Where does the external render finish at the bottom? - it needs to be above the DPC not below it.
You may need to hack off the hollow render and do it again, also you need to check the internal plaster that it's not all the way down to the concrete.
More information required for a proper diagnosis
Hi all,
thanks for the replies.
The damp is in the inside of the external walls but also in the dividing wall.
It goes up about 4 feet.
The plaster seems to stop about an inch above the floor.
I say it's *in* the walls. The bricks are actually damp.
There's no radiator in the kitchen but I had one put in the extension. It seems to dry out the wall until it rains again.
It could be that the DPC has been bridged but I can't even see a DPC to be honest. The bricks were painted black. The paint had peeled about below where the patch of hollow render is.
Could it be a water course under the extension?
Thanks again all.
And to add, the render finishes about 2 feet above the ground and is curved outwards, which I assume is to stop rain dropping inward.
seems to dry out the wall until it rains again.
e honest. The bricks were painted black. The paint had peeled about below w= here the patch of hollow render is.
If an internal wall is damp that points to either a massive temperature/humidity difference between the two sides of the wall or faulty damp proof course. What sort ofDPC is fitted? If it is the felt it is probably OK If slate/engineering bricks it might not be.
ing about all this) can cement rendering cause dampness on internal walls?
low" though it was fixed and the dampness is more noticeable after rain. Al= so both rooms have a concrete floor.
seems to dry out the wall until it rains again.
e honest. The bricks were painted black. The paint had peeled about below w= here the patch of hollow render is.=20
rved outwards, which I assume is to stop rain dropping inward.=20
The most likely cause is condensation, caused primarily by too high an inte= rior RH. This type of thing is often misdiagosed as rising damp, which alth= ough it exists, is unusual. The solution is normally to address interior so= urces of dampness, eg showers without adequate ventilation, hob cooking on = excessively high heat, drying clothes indoors, unvented gas heating, inadeq= uate ventilation in rooms etc.
The gradual movement of water vapour is from interior to exterior, since in= terior RH is higher on average. Thus evaporation of water from the exterior= of the wall is necessary to avoid dampness. You mentioned a black paint, i= f you mean bitumen on the exterior then this can gradually cause damp probl= ems by preventing evaporation. Painted cement render can occasionally too i= n walls that are borderline in terms of how they handle damp, but that's no= t likely to apply to a cavity wall. Are you sure they're cavity walls, as e= verything you describe is a lot more likely to occur with non-cavity walls?
NT
Thank you for that glimpse into 1950s Britain before central heating was the norm
Damp, the subject you can't be bothered to read up on
Where do you get the idea that indoor RH is normally higher than outdoor? Do you live in a cave?
Probably lives in Scotland. :-)
Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.
So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.
NT
RH is all about water vapour.
If the interior water vapour is going through the wall then there is no evaporation at the outside.
If that water vapour is condensing in or on the wall, that is a different matter.
vapour into the indoor air.
out through walls.
The warm air indoors is quite able to carry a bit of extra moisture, so it doesn't go anywhere. In fact, in what I would term a normal household there is more danger of low rh than high but, if you're not going to maintain a temperature fit for human habitation, then there won't be much difference between inside and out. No way to live though
vapour into the indoor air.
out through walls.
People keep breathing, washing and cooking, so water keeps being put into the interior air. If it really went nowhere, it would condense out and flood the house. Its pretty obvious it goes somewhere.
In some cases yes, in some the reverse.
Unheated houses have higher indoor RH than out because of the constant supply of water vapour from breathing, washing and cooking.
Seriously you need to get this figured out beore you can understand how damp works.
NT
All I need to figure out is why you appear to be living in the land that time forgot.
I know you know where the dividing wall is but I don't, the dividing wall between what?
rising damp
you'd be wise to knock off another inch or two
Then it needs a dampcourse, you can DIY, providing you know how to drill a hole
Water is getting behind this patch of hollow render, and running down, which has caused the paint to peel.
The DPC is the level of your internal floor
No
Sorry, the dividing wall is between the kitchen and the extension, both have the concrete floors.
I had a chemical DPC done by a plasterer a few years back.
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