Damp & salt marks either side of a bay window exterior is pebble dashed painted in good condition marks are approx 1.0m from ffl

Question

Short marks to internals either side of bay window exterior is purple – and painted in very good condition

Mark appear 1 m above FFL skirting levels in good condition

Could they be condensation??

They rented area on the outside as bridged at the stamp roof of course could it be this??

Che · Accepted Answer

Hi I'm suspecting water is getting in either side of the window sill .check for any gaps and lack of silicone

Mark · Answer

Maybe you need damp course fix each side of the bay but I would run across bay as well injection

Peter · Answer

Hi Anthony
Sorry can’t help with repair as this is not our field of expertise 
However it sounds like the rain is getting in behind the pebble dash and crossing over through the cement across  cable ties which join the out wall to the inner wall would of been put in when house was built

Darren · Answer

Yes, condensation is certainly one possible cause of marks appearing internally on either side of a bay window, particularly if the affected area is cooler due to thermal bridging around the roof junction or external wall detail. Even where the exterior render and paintwork appear to be in good condition, bridged or poorly insulated areas can create cold spots that attract moisture from indoor air, leading to staining or damp patches around 1m above floor level. However, it’s also worth ruling out water ingress from flashing, roofing details, or failed seals around the bay structure, especially if the issue worsens after heavy rain rather than during colder weather or periods of high indoor humidity.

Martin · Answer

From your description, I wouldn't immediately assume this is condensation. Salt deposits and damp staining appearing approximately one metre above floor level on either side of a bay window often indicate that moisture is entering the wall from an external defect rather than being caused by normal household condensation.
The first areas I would inspect are the roof covering above the bay, the lead flashings, gutters, downpipes, pointing, render or pebble dash, window seals and any junctions where water could penetrate during heavy rainfall. Even if the external render appears to be in good condition, very small cracks or failed seals can allow water to enter and travel through the wall before becoming visible internally.
If there is a flat roof over the bay window, this should also be inspected carefully, as ageing felt, damaged GRP, failed joints or defective lead flashings are common causes of water ingress. Bridging of the damp-proof course, high external ground levels or debris against the wall should also be ruled out, as these can contribute to damp issues.
The white salts you are seeing are known as efflorescence. These are left behind when moisture passes through masonry and evaporates, bringing natural salts to the surface. While the salts themselves are not usually the problem, they are a strong indication that moisture is present and the source should be identified.
Before considering any damp-proofing treatment, I would recommend arranging a thorough inspection by an experienced contractor who specialises in diagnosing water ingress. The priority should always be to find and repair the source of the moisture first. Once the external defect has been resolved, the wall can be allowed to dry naturally before any internal repairs or redecoration are carried out. This approach provides a long-term solution rather than simply treating the symptoms.

Damp & salt marks either side of a bay window exterior is pebble dashed painted in good condition marks are approx 1.0m from ffl

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