Rising (?) damp

Siliconslave · 11 Dec 2018 at 14:30

My house was built in the 1870s and has a thick, brick cavity wall setup. We appear to have damp in the bottom of a north west corner of an external wall.

Its been totally dried out (using a dehumidifier) and has come back and is litterally running with water. Over the summer we re-painted the outside of the house with a breathable exterior paint so pretty sure its not transference from outside & theres been no flooding locally.

There appears to have been a damp proof layer installed at some point as there are holes along the outside of the property, along the mortar line below floor level however we have no documentation about it anywhere.

Can't see any other water damage and there aren't (as far as i'm aware) any leaks in the area - drainage from the roof is all good (replaced over the summer as well) so all I can think is that theres rising damp.

Has anyone self installed a damp proof layer like dryrod? wondering if i can do it exclusivly from outside or will i need to pull plaster off the inside...

eviled · 11 Dec 2018 at 14:53

are you sure its cavity? possible but rare if 1870s

if there's that much water then its likely a leak still, if your happy its not guttering or an overflow pipe then I would check the drains next.

Do you have a suspended floor to gain access underneath?

Siliconslave · 11 Dec 2018 at 15:22

I guess i'm not 100% on that wall but have drilled through a different wall of the (old bit) of the house & it was certainly twin skinned.

there is a suspended floor so yer, will be pulling that up next i guess!

Molep · 11 Dec 2018 at 16:00

If there are holes along the outside - the cavity may have been filled under the premise of insulating the property. I'm not convinced rising damp is a thing really - there's only so far moisture can travel up by capillary action.
My own 'damp' cold areas have been remedied by reinstating air flow, like airbricks, uncovering grils etc...
Maybe under your floor there are blocked air flow bricks etc..
Check out this site for ideas as to where the moisture could be getting in - https://www.heritage-house.org

something daft already!! · 11 Dec 2018 at 16:10

Oh Miss Jones!

topgun06 · 11 Dec 2018 at 16:35

Molep said:
https://www.heritage-house.org

This guy is a wealth of information!

Foghorn Leghorn · 11 Dec 2018 at 16:59

Old houses need to breathe and need good airflow, they aren't designed to be sealed like modern houses (painting exterior walls is not a good idea, even with 'breathable' paints) If you've eliminated all possibilities of water ingress from outside then it'll be condensation. The northwest corner of your house is most likely to be the coldest as it is unlikely to see much if any sunlight over winter, corners of rooms are the worst especially behind furniture such as wardrobes as there is no natural airflow.
The moisture comes partly from the air, from your breath but mostly from cooking and drying clothing on radiators. The air becomes saturated during the day then as the air cools at night it condenses on the coldest areas in the house, in modern houses it's windows, in old houses it's the walls due to lack of a cavity/insulation.

Siliconslave · 11 Dec 2018 at 19:03

hrm... we did block the chimney up recently to prevent cluster flies getting down - wonder if thats contributed. Will have to have a look at alternatives i guess!

Aberfala · 11 Dec 2018 at 19:43

While I'm certainly no expert a couple of things you did mention were very similar to a house I was in the process of buying recently until the survey put me off.

Firstly, you mention the walls being twinned skinned, this is quite possible, in the house I was looking at the was built some time in the 1920's-30's the walls were twin skinned but bonded together rather than cavity. This I was told was standard practice for the period.

Secondly, The house I was buying had had the chimney blocked up at some time in the past few years without leaving any ventilation (normally an airbrick is used) which caused the entire area around the chimney to be very damp. Did you install an airbrick ?

Thirdly, the plaster may still look damp due to salts coming through and becoming hygroscopic. The only solution is strip the old plaster off completely to a point about 300mm above the previously damp plaster and replaster.

I hope this helps.

Siliconslave · 11 Dec 2018 at 21:55

we've had hydroscopic plaster in the past in a different place but this is significantly wetter that that ever got. The 'blocked' chimney is actually a flue with a chimney balloon in so will look at taking that out and replacing with a mesh to get more airflow...

Skillmister · 11 Dec 2018 at 22:45

Siliconslave said:
hrm... we did block the chimney up recently to prevent cluster flies getting down - wonder if thats contributed. Will have to have a look at alternatives i guess!

When I moved into my house last October the air vent in one of the chimneys was totally blocked with dog hair etc. As a result moisture which was getting in down the chimney was saturating through the brickwork/plaster and tracking across the carpet. The carpet was damp across the entire living room/dining room and the underlay was rotten. When I removed the vinyl wallpaper from the chimney I touched the plaster and my hand was soaking wet!

I did nothing but unblock the air vent completely and have a good hoover out of the base of the chimney and its been completely fine.

Tl:dr
Don't underestimate what effect a bit of constant moisture and lack of ventilation can do over time

balls · 12 Dec 2018 at 08:25

Worth batoning +insulating and plasterboarding over the damp wall?

Siliconslave · 12 Dec 2018 at 09:27

balls said:
Worth batoning +insulating and plasterboarding over the damp wall?

would much rather fix than hide tbh

balls · 13 Dec 2018 at 08:21

Siliconslave said:
would much rather fix than hide tbh

I'm always skeptical about rising damp, it sounds more condensation related which would be sorted by a new stud wall

Foghorn Leghorn · 13 Dec 2018 at 10:33

It'll depend on the room, heating system and reason for the amount of moisture. Studding the wall and insulating behind it may work or it may move the problem somewhere else.