Very narrow strip of damp at floor level

[Georgie73]

Hi we are currently renovating our new house - downstairs has concrete floors. House is about 70 years old.

On an external wall there was a piece of skirting board which just crumbled (from the base) as soon as you touched it. I've taken it off and also as we stripped the wall paper on the same external wall - all the plaster just crumbled so have taken it back to the brickwork.

At the floor level, there is a gap between the concrete floor and the external wall, it is about 15 mm wide and about 7 foot long . The concrete floor is solid as in no problems and I can see the DPC on the brickwork of the external wall. However, this tiny little gap is allowing damp to rise up and penetrates the skirting board and I guess over the years it has also affected the plaster.

Which is the best product to treat this damp issue in this very tiny area?

Many thanks
George

 

[foxhole]

Gap is of no consequence, you need to check the outside for source of damp, or could be condensation soaking the skirting, do you have good ventilation?

 

[Georgie73]

Ventilation is good.

I've just popped outside to look at the wall and there is an airbrick just below the damp proof course. That is confusing me as the floors are solid and I thought the airbrick is to help air flow. There isn't an airbrick on the inside.

 

[TheVictorian]

Probably used to have a suspended timber floor and they have concreted it at some point. The gap is probably where the concrete stopped if there was previously plaster/skirting there. The airbrick is likely redundant and could be removed and bricked up.

A picture would probably help.

 

[foxhole]

Ventilation is good.

I've just popped outside to look at the wall and there is an airbrick just below the damp proof course. That is confusing me as the floors are solid and I thought the airbrick is to help air flow. There isn't an airbrick on the inside.

Air brick may be to allow ventilation to inner timber floors? are all floors now concrete or just some.

 

[Georgie73]

All downstairs floors are concrete. No timber floors except for upstairs.

 

[vinn]

Your best bet would be to post photos of the inside area of revealed damp, and the corresponding outside area.

Meantime, strip any remaining skirting from that wall and examine it.
Did the plaster behind the skirting run down to touch the solid floor: or go below it?
Is that wall totally hacked back to the brickwork now?
From your post you dont seem to have a membrane (DPM) under the concrete slab. Lack of a DPM could allow moisture to rise to the floor surface.
The internal wall DPC should be above the solid floor.
You should have a cavity but if its blocked and bridging the DPC's on the outer & inner walls then moisture could be penetrating the inner wall at low level.
Is the inside floor level higher than the outside ground level?

 

[Georgie73]

Your best bet would be to post photos of the inside area of revealed damp, and the corresponding outside area.

Meantime, strip any remaining skirting from that wall and examine it.
Did the plaster behind the skirting run down to touch the solid floor: or go below it?
Is that wall totally hacked back to the brickwork now?
From your post you dont seem to have a membrane (DPM) under the concrete slab. Lack of a DPM could allow moisture to rise to the floor surface.
The internal wall DPC should be above the solid floor.
You should have a cavity but if its blocked and bridging the DPC's on the outer & inner walls then moisture could be penetrating the inner wall at low level.
Is the inside floor level higher than the outside ground level?

I've got pictures on my phone so I will have a go at uploading them a bit later on.

There isn't any damp coming up through the conctrete floor anywhere - it is solid and free of any moisture. The wall has been totally hacked back to the brickwork. The plaster went down to the floor. It did not go below the floor as the floor is solid concrete.

The walls do have a cavity and I believe they were injected with insulation a couple of years back. The internal wall DPC is visible and it is one and a half brick above the concrete floor. The inside floor level is about half a brick higher than the outside ground level.

Will post pictures later.

 

[vinn]

Your plaster was bridging your DPC.
Is the outside wall rendered?
Cavity insulation is often suspected of bridging the cavity with moisture coming from the outer skin or up from any rubble in the cavity.
Gaps dont allow moisture to rise up.

 

[Georgie73]

The outside from ground level up is 10 courses of brick in height and above that it is rendered.

Are you saying the inside plaster must finish above the DPC?