Penetrating Damp


There are many causes for penetrating dampness


  • Defects to the external construction of the building works: poor roofing, ingress of water through uncapped chimneys, especially unvented blocked chimney breasts. cracked render & brickwork, blocked or damaged guttering, broken & corroded downpipes, poorly fitting or rotten door frames & windows, all of which can allow rainwater to penetrate into the fabric of the building.

  • Lateral penetrating damp: where external ground levels adjoin the building higher than the damp proof course. Lateral dampness is frequently encountered on properties with basement flats, cellars or those built on sloping ground.

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Identifying Penetrating Damp


There are many indicators that surveyors use in identifying penetrating dampness, as with rising damp, many clues will exist outside the property where the building construction and general condition is key, the rainwater goods and the soil levels outside the property are checked.


Where penetrating damp is due to high ground levels it is often referred to as lateral penetrating damp. Soil levels may not be the only culprit in this case, other external wall materials in contact with the wall may cause this ie building rubble, garden refuse, decking etc.


Internal signs to look for when trying to determine if the cause of problems is the pattern of moisture readings given using a damp meter.



Dis-colouration of the internal décor with the presence of tide marks, salt deposits.


Blown/blistered (hollow sounding) plaster. Wet and/or rotting skirting boards and floor timbers, sometimes exhibiting rusting nails, Random damp patches to any height on the walls and ceilings. Black mould on internal walls (a Condensation issue) can be observed due to the coldness of the building fabric being increased through penetrating damp.


The solution;

Where the problem is identified to be normal penetrating dampness, the root fix is to address the necessary building repairs (roofing, guttering, external rendering etc) The results of this problem sometimes requires replacement of internal plasterwork and timbers affected by water ingress.

Lateral penetrating damp requires a very different approach. The internal walls to the affected area will probably require a form of tanking,

Cementitious Tanking involves taking the wall back to its raw state, typically removal of plaster and render to the exposed brickwork. This removes all the salt contaminated finishes that would continue to be a harbor for dampness whether created from external water ingress or internal moisture. The exposed raw wall will then be rendered with a sand and cement backing coat that contains the appropriate waterproofing agent ie Sika 1. The backing coat will then be skimmed with the appropriate finish plaster.


Membrane Tanking involves sealing the wall with a waterproof membrane (as shown) before dry lining & re-plastering, in some cases where continued water ingress probable we recommend installing a raised floor with a sump and pump below. This subject is covered in more detail on our page entitled Basements that


takes a deeper look into problems and solutions for basement areas, a common environment that suffers from lateral penetrating dampness. This method generally causes less disruption, only loose plaster/render and any organic materials require removal.


A professional remedial survey is highly recommended in such cases as mistakes in diagnosis are commonplace, errors can result in unnecessary and costly works that fail to control the dampness. Garratt’s Damp & Timber Ltd provide free surveys and reports, with impartial, honest advice on the options available to the customer.


Contact Garratt’s Damp & Timber Ltd today for free, honest advice.

0208 535 7536

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