Be Your Own Surveyor, External Walls – Inside.

Be Your Own Surveyor, External Walls – Inside.

There are three main types of damp and outside walls are prone to all. I’ve already covered this in detail in previous blogs.

In summary, rising damp doesn’t usually travel beyond 1.2 metres above ground level unless the masonry is very hydrophilic (attractive of moisture). It shows itself by damage to plaster and efflorescence. This is white crystalline deposits of sulphur and carbonate salts from soil or masonry, dissolving in moisture and coming to the surface, giving a blistered appearance to the plaster. It can be treated by injection (£500 or more for a typical terrace).

Penetrating damp can also cause efflorescence. It can appear anywhere, from multiple causes. Faults with masonry include porous stone or brick, loose render (the cement outer coating of the wall) and deteriorating pointing (the cement finishing between bricks or stones). These may require scaffolding to rectify and can be expensive.

Penetrating damp unconnected to the masonry includes leaking gutters and downpipes, dripping overflow pipes, leaky roofs, water splashing over the hopper where the gutter joins the downpipe, and earth piled high against outside walls acting as a conduit over the damp-proof membrane (DPM). Most are easily and cheaply rectified.

The third type, condensation, appears on cold surfaces such as single-glazed windows where it runs down and damages the sill and walls to the sides, or on outside walls where ventilation is poor, such as behind wardrobes or inside cupboards. Insulating well and removing furniture from outside walls, plus putting in a mobile dehumidifier, will help.

Other issues are corroding metal wall ties on early 20th century cavity walls. Early cavity wall buildings up to the ‘40s or ‘50s are prone. Modern ties are galvanised or plastic, and designed so that condensation doesn’t settle but drips off the middle and down the cavity. It can be very expensive to get remedial work done. Unfortunately there’s no simple way of telling unless the brick skins have already started to separate and become unstable.

‘Concrete cancer’ is a problem of system-built (prefab) buildings from the mid 20th century, with pre-cast concrete walls. It’s caused by efflorescence of salts damaging the concrete and corroding the reinforcing rods. That’s why these buildings are generally unmortgageable, although many may be structurally sound.

Modern houses should have out-and-down facing cavity trays of plastic or lead above openings (windows and doors), cavity closers at the sides and a folded-over plastic DPM underneath. This prevents water migrating from outer to inner skin across the cavity at the window reveals (sides). If there is evidence of damp migrating in around openings, the trays may be faulty or missing.

I’ll write about assessing wooden floors next week.

All the best,


These blogs are not intended to replace the services of a surveyor, engineer or other professional. They may however help save you the expense of a surveyor for a duff building that you won’t buy.


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