What is Rising Damp?

What steps should I take to stop it?

Rising Damp Facts

Where water is evaporating there will be a definite line where the salts stop, caused by capillary action. This is ground water rising through the wall.

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WHAT IS RISING DAMPNESS?

In a solid brick built wall with no cavity affected by rising damp there are some basic signs.

You need to first rule out condensation on the inside that may show up as damp plaster or paper just above the skirting with or without black mould.

With rising dampness there is not normally black mould, but on the face of the plaster or paper you find hygroscopic salts as a powder. Where there is water evaporating there will be a definite top line where the salts appear, which is the highest level of rising dampness. This is where there is capillary action of water rising through the brick from the ground moisture.

On the outside of the wall on brickwork you should see definite salts showing coming to the surface.

If the inside finish of the wall is not finish plaster on brick or block, but plaster or plasterboard on timber battens it can be more difficult.

To decide you can eliminate the following:

1. The problem could be plaster, brick or mortar dust packed behind the skirting and transferring moisture to the surface.

2. If higher than 1200mm or isolated to one part of the room it could be penetrating dampness from a leaking downpipe, bridging from a garden wall, high ground levels or wall ties covered with mortar.

3. You need to test moisture contents in a number of areas.

4. A further cause could be where a terraced house is on a hill. Next door floor levels can be higher than your house. In that event you need to consider your house as a basement. [See Penetration Dampness (Basements)]

Rising Damp

An example of a recommended treatment for rising damp - where there is brick or solid stone masonry including sandstone: [d]

  • Strip back plaster approximately 300mm above the levels of salt or high moisture content.
  • Treat walls with a salt inhibiter.
  • Predrill holes 2 per brick or into mortar joints internally and externally at 150mm centres for masonry.
  • Inject silicon based DPC fluid, stick or gel paste.
  • Re-plaster base coat renovating plaster or 3:1 sand cement with plasticiser and salt inhibiter.
  • Do not let base coat plaster to bridge the damp proof course.
  • Apply 3mm skim coat finishing plaster.
  • Keep all plaster 25mm above floors and use a timber strap with DPC damp course behind to fix skirtings to.
  • Fit skirtings and paint, paint plaster with microporous paint like anti-condensation paint.
  • Fill injection holes externally with pigmented mortar.

Credits

[d] Source of product descriptions - https://www.sovchem.co.uk.

Hey’di Antisulphate is used to treat damp, salt affected masonry.

Hey’di K11 Bonding Agent provides greatly improved adhesion and resistance to water and the passage of salt.

Renderlite Renovating Plaster  An easy to apply internal plaster; breathable; salt resistant; excellent thermal qualities. Reduces condensation.

Renderlite Finish Plaster Gypsum based plaster Final coat. Hard wall finish plaster Allows walls to breathe.

[Suppliers available for products] See - https://www.sovchem.co.uk/where-to-buy/.