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How To Treat Damp Walls Internally

Updated: Sep 7, 2023


T : 020 7862 6363


Damp to internal wall

In this blog post, we are going to look at how we can treat damp walls internally within a house.

Prevention is Better Than Cure

The first thing to remember with damp to a internal wall is that 'prevention is better than cure'.

In older buildings, damp stains on internal walls are usually due to external factors such as: 1. Leaking rainwater gutters 2. Misdirected rainwater downpipes 3. Insufficient external drainage

4. Poor drip details to cills and other protrusions

5. Bridging of the damp proof course (discussed below)

6. Condensation

Case Study 1: Victorian House suffering with damp.

Take a look at the below real life example where we surveyed a Victorian house in London that suffered from internal damp walls. We initially observed damp staining to the wall and ceiling junction near the bay window of one of the first floor bedrooms:

Internal wall damp stain
Damp staining to internal wall junction with ceiling

Our surveyors tend to be undercover detectives and love a good challenge in solving building defects!

Going outside, we realised that the plain clay roof tiles just above the guttering had 'slipped' and there was a section of roof where the roof tiles were missing. This could allow rainwater to ingress via the roof space but also, cause rainwater to 'miss' the gutter and instead saturate the brickwork below.

Roof leak causing internal damp
Slipped tiles to roof causing water ingress

We cracked it! or did we?

Within the same house, we spotted another internal damp wall. This time it was a ground floor living room wall facing the rear..

Damp internal wall
Location of damp to internal wall

And so outside we ventured again to find..

external area causing internal damp
Problematic external area that was affecting the internal wall

a) We found that the timber door threshold stopped flushed with the external wall. There should normally be a overhang and threshold drip detail which prevents rainwater to track back into the building. The flush threshold was problematic and could allow rainwater to track back into the building.

b) We found heavy moss growth to the external ground in close proximity to the internal damp wall. We also noted the ground sloping towards the property. This could allow rainwater to stagnate and percolate back into the property.

c) Lastly, we were not a fan of a brick garden soil bed that abutted to the external wall in close proximity to our internal damp wall. We felt that this could bridge the damp proof course (meaning that rainwater how now a hop up over the damp proof course and into the property).

Case Study 2: Damp and moisture to upstairs bedroom wall.

On another building survey for a Victorian Terraced House, we found high moisture content on the internal wall finish which was facing an external elevation.

Damp staining to bedroom wall facing the front elevation
Damp staining to bedroom wall facing the front elevation

So how do you go about treating damp on a upper floor? Where was the damp coming from? We took a quick look outside of the window to find....

Leaking rainwater gutter causing damp to internal wall
The Culprit: Leaking rainwater gutter

A leaking gutter. The good thing (or lucky thing) about the timing of our survey was that it had rained heavily the night before. This meant that we were able to see remaining rainwater from the gutter leaking and saturating the external brick wall directly underneath...

Water stained brickwork - a sign of gutter leaks
Water stained brickwork - a sign of gutter leaks

A good sign of brickwork being subjected to rainwater from guttering leaks is discolouration and darkening of the brickwork which we can easily spot from the picture above.

We advised the client to repair the leaking gutter and wait for the internal wall to dry before thinking about renewing the decorations.

So now all of the external bits are sorted, how do we treat internal damp walls?

Let it dry! that's right. The first course of action would be to let the wall dry out completely. The last thing anybody wants to do is redecorate a wet wall for the decoration to only be spoilt in the near future.

The below steps should help in treating an internal damp wall:

1) Ensure there are no external factors allowing water into the property (as discussed above.

2) Allow around 3-4 weeks per 25mm of solid brick wall as a rule of thumb for drying time. So if you have a brick wall that is 225mm thick you should wait two month at the very least before thinking about any decoration.

3) If painting, apply a coat of stain block. Stain block solutions help mask over damp affected paintwork and prevents damp stains bleeding through newly applied paint.

ZFN Chartered Surveyors are fully regulated by the Royal Institute of Chartered Surveyors (RICS). If you are interested in any of services then feel free to contact us on 0207 862 6363. ZFN CHARTERED SURVEYORS

T : 020 7862 6363



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