This post continues the series on dampness in Buildings. It concernsHorizontal Damp, both the cause and the remedies for horizontal dampness.

Causes of horizontal dampness

Horizontal dampness occurs when water moves in a horizontal direction through walls.

Whilst this can be caused by unsealed penetrations in the wall and other like defects, it is most often caused by direct rain against badly porous brick or stone walls or when earth breeches the damp proof barrier. It is a common problem when there is earth against the brick or stone wall, such as in a cellar.

It can also occur from poor bricklaying practices when mortar droppings left on the cavity ties joining the two walls forming a bridge for water to cross.

If the inside of the wall becomes damp during rain and then dries out after it is probably due to rain penetration.

Whatever the cause this form of dampness is like all others. It should be removed from internal walls to avoid health issues for the occupants as discussed in a previous post on this blog page.


Remedies for Horizontal Damp


By far the best remedy for horizontal damp is to consult an expert in damp.

Isolated patches can be repaired by painting on a waterproof plaster coating to the outside of the wall, if accessible. Gaps or cracks in the mortar need to be repaired before applying any coating.

Plaster affected by the damp penetration will likely need to be removed and the wall replastered.