103Z: Hygroscopic salts manure

A large Victorian double fronted house with hygroscopic salts up to about 3M high on the front wall.

Surveyor Tips:

  • Hygroscopic salts have previously been used as a justification for rising damp treatment.
    • The property is not at risk of rising damp.
    • The height of the rise is greater than could be accounted for by rising damp.
    • It is far more likely to be cause by rainwater causing salts to redistribute to the level of equability.

Root cause

Root cause hygroscopic salts probably from use of manure to front flower bed.


The primary concern is a series of damp patches to the front wall.

These damn patches take the form of moisture without crystallise salts and mould, typical of excess vapour and without damp staining, typical of a leak or penetrating damp. These, often random damp patches a characteristic of hygroscopic salts.

Using a radio frequency damp meter I found damp from about 3M off the external ground level.

Rising damp has only been demonstrated to rise up by a few courses of bricks, it is also has a very horizontal profile, like flood water.

You sent me this image asking about visible damp on the outside of the property.

Calcium nitrate the most common hygroscopic salt only causes deliquescence, that is a form of condensation, when humidity it above 50%RH, otherwise bricks look dry.

Here is an image of the property during the survey the dark colour is visible but less distinctive.

Overtime moisture binds onto pollutants such as soot, so that hygroscopic salts in many walls subject to industrial pollutants always look dark. Mortar tends to be more absorbent than brick and so tends to discolour more, see you later in this report.

Similar characteristics are true of the front left-hand side, although here we can see splattering of mud.

This is a useful Image as it clearly shows that raindrops can bounce up a wall, well above the damp proof course (in line with the air vent). Moisture moves through rain, condensation and evaporation, see a Youtube video sent to the PCA; https://youtu.be/EeT05HxvAs0

Again here is the photo taken during the survey where are the effects of hygroscopic salt are not visible.

You sent me this photo for comment, but we didn’t take a look at it.

There appear to be some hygroscopic salts in the centre, presumably some of the bricks have been replaced. The green tell me that water is flowing onto the wall, probably leaking out of the rainwater butt.

Chimney breasts are the most common sources of hygroscopic salts.

These salts are typically released when chimneys altered or anyway replastered.

At the time of the survey there were no visible signs of dampness on the surface.

A high damp meter reading in radio-frequency mode suggests that there are salts deep within the chimney breast. It would be advisable not to replaster this chimney, otherwise hygroscopic salts it likely to emerge.

Damp wall

Under the front right hand bedroom window there is a damp stain.

Stains come from water that has flowed through building material such as brickwork, picking up colour from the substrate on its way, in this case penetrating damp from the rain on the outside.

Damp wall

Using a damp meter in surface conductance mode I tested and found that the wall was dry.

Protimeter damp meter in conductance mode measure electrical conductance of salts in water, a proxy for damp. Readings below 20WME are considered dry. The range is 8WME to 99WME. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.

Damp wall

Looking immediately outside there is a crack in the windowsill, probably an original feature.

Small cracks can draw in a lot of water like capillaries. You should rake out and paint the crack, possibly sloping the sill slightly away from the crack to reduce the risk of water pooling above any future cracks that could return.

Damp wall

There are few minor cracks in timber I don’t think these would’ve caused ingress.

Damp window frames can result in Phellinus contiguus or window rot. Window rot is very common in old properties, it is a slow growing white rot. None of the timbers are appeared affected. If they do, then rot can be cut out, sanded, filled and painted for protection.

While I think the most likely cause is penetrating damp from the outside I cannot rule out condensation on the inside, I therefore encourage you to monitor relative humidity.

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