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  • Writer's pictureSam Costigan

How to Fix Damp - Part 3 - Contributing Causes

In recent weeks we have written part 1 and part 2 of our damp series regarding a recent building survey we carried out. The subject property is a great case study as there are multiple different contributing causes for the damp.

Before we get into it, for any students reading this, I want to make clear that I don’t disbelieve that rising damp exists; because it has been proven by people a lot more decorated than me, that it does exist. I just believe (from experience) that rising damp in the traditional sense of a failed damp proof course is extremely rare.

How we approach damp investigations

British Standards BS 6576:2005 + A1:2012 “code of practice for diagnosis of rising damp in walls of buildings and installation of chemical damp-proof courses” states the following:

“ - When inspecting a structure for signs of rising damp, it is essential to take into account the possible presence of other sources of dampness…”

“ - All other possible causes of damp conditions should be located particular attention should be paid to…

  • condensation

  • lateral penetration

  • leaks

  • faulty drains

  • internal plumbing

  • penetration through external walls

  • penetration around window frames and doors

  • mortar droppings or debris in the cavity

  • history of flooding”

“ - If positive evidence of rising damp is being obscured by other faults such as those described in it is preferable that those faults should first be remedied and that and appropriate period of time should be allowed to elapse before making further checks to ascertain the presence of rising damp”

In following the above basic principles, we are able to find possible causes of the dampness and create our schedule of repairs based on our findings. 99 times out of 100, these repairs are simple, easy to do and cheap therefore this principle offers incredible value for money to our clients.

Damp - other contributing factors at the subject property

At this particular property we have already discussed in part 1 and part 2 regarding ground levels, blocked cavities and blocked air bricks.

This blog is going to explain how one other external factor has led to increased moisture in the external walls - defective render.

The subject property has a brick facing cavity wall at ground level with the upper floor being rendered. Where the render finishes at first floor level, a drip detail has been created to divert rainwater away from the face of the ground floor walls.

This drip detail is often referred to as a “bell drip”, “bell mouth”, or “bell cast” and it acts in the same way as a windowsill. Rainwater running down the face of the render reaches the bottom and due to the detail, it drips off, rather than running back against the wall.

Rendered walls with drip detail

Understanding the background of this property we established that very little maintenance had been carried out and that the render was cracked and weathered. Part of this weathering was that the drip detail had degraded so much that it was no longer diverting rainwater away from the brickwork below. We established this by the efflorescence on the brickwork, the weathered mortar pointing directly below it, and the frost damaged bricks. All of this combined was allowing the external wall to be constantly saturated from excess rainwater.

Furthermore, in part 1, we explained that we had established that the cavity was blocked at low level and this blockage was forming a bridge for water from the outside leaf, to the inside leaf where visible decorative spoiling was occurring.

We also established in part 1 that one of the sources of moisture ingress at low level was the damp proof course being bridged, mixed with the cavity also being bridged.

This additional moisture run off from the defective render, mixed with faulty mortar pointing was allowing moisture to enter the cavity higher up the wall, filter down the cavity and saturate the debris, where it then transfers across to the internal face of the wall.

Decorative spoiling follows the same line where the cavity is blocked


From conversations with our client, we understood that they have plans to renovate the property which included a budget to replace the render. The good news for our client is that replacing the render and correctly reinstating the drip detail would once again divert rainwater away from the ground floor, something which they had already budgeted for.

In part 1, we specified remedial works to reduce ground levels, clear the blocked cavities and repoint any areas of saturated, defective and crumbling mortar. This combined with replacement render should prevent further moisture ingress and damage to the bricks.

If you are suffering from damp and need professional help, please feel free to get in touch using the below info.

Sam Costigan

Chartered Builder | Managing Director

Tel: 0113 887 1941

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