A ROGUES GALLERY OF DAMP AND IT'S CAUSES

The following are a selection of images taken during various site visits, for many it is simply too late for them to justify the use of lime, given that they have usually laid out a lot of money for “remedial” works to have been carried out, or the thought of doing exactly the same again simply using a different binder is untenable.

   
Radical actions to address a damp problem
above left - bitumen paint, above right - tin cladding

The property shown below is situated in a very exposed part of north Cornwall with the frontage (illustrated above) facing South West. The construction is from a local sedimentary stone with brickwork to all of the quoins and reveals. The present owners appointed a Surveyor to prepare a specification for the necessary remedial works, in order to overcome the damp problems being experienced especially around the window reveals.The property had been “dealt” with in recent years using sand and cement, as was the case here for the pointing. Rendering was called for as the way forward (by the surveyor) and following consultation with CLC a St.Astier NHL 3.5 was used in a three coat system

  
left: before, cement pointing = damp. right: after, NHL 3.5 render no damp

The image (below left) show the type of problems being experienced prior to the remedial works being carried out, and more recently (right), which is now two years on from completion.

   
left: damp on a Cement/Gypsum Background
right: NHL 3.5 render externally.  Problem solved - it is that simple!

Passmore Edwards Building. Truro Library

The image on the right shows a cement render failure on a soft sedimentary stone to Truro Library, a building in the care of Cornwall County Council. However, what this image can’t portray very well is the damage that has been caused as a result of the cement’s use on soft stone, and the damp problems the fabric was suffering as a result of this.

Extensive repair works have been carried out on this building over the last two years with the render to the internal and external wall surfaces being hacked off and re-rendered (externally) during the winter of 2000 using NHL 3.5 with the internal walls being allowed to dry out for twelve months, and then rendered using a mature lime putty render.

The cracking that is evident in the above image clearly illustrates how unsuitable a cement render is on fabric that is inevitably prone to thermal movement etc. and cements inability to accommodate this phenomenon.

This particular building has been subject to monitoring (to the rooms where works has been undertaken) both prior to, and following the works, as part of the surveyors ongoing studies into the use of cement V lime on older buildings and the evidence gathered thus far is overwhelming in favour of the lime approach. A fact we have been personally aware of for many years, but it is very reassuring to have an empirical understanding backed up by scientific methods. The testing methodology has been undertaken as part of a PHD study using a combination of Protimeter Hygrosticks and Data loggers.

Many other buildings under the care of the same Surveyor where lime has been used, have also been closely monitored and the results when published should make very interesting reading. We are certainly encouraged with the limited information we have been offered thus far and it will be his intention to submit a résumé in the Journal of the Building Limes Forum in due course.