Traditional and listed buildings especially timber framed buildings that are suffering with rising and penetrating damp need to be surveyed by a competent surveyor. The surveyor should have a good understanding of how these buildings are built, this gives the advantage of knowing where to look, and what to look for, and what sympathetic repairs are needed to preserve the long term future of the building.
Our surveyor is a qualified and registered surveyor in dampness and timber decay and infestation with the Property Care Association www.property-care.org and is also a member of SPAB wwwspab.org.uk
He has a wealth of experience of listed buildings and traditional repair methods that sometimes need help with a modern sympathetic approach like structural repairs using helibar systems tieing in the building.
To help us identify the dampness we have a range of specialist equipment. We use the Flir MR77 that sends moisture readings via bluetooth to our thermal imaging cameras that help to map out the moisture, this helps us to understand the dampness in greater detail in a thermal image. We also use thermal imaging to locate timber framing that has hidden behind plaster.
Our surveyor is also a qualified level 1 thermographer so we can interpret thermal images to give quantitative results.
We also have our own laboratory where we use gravimetric-oven dry analysis to BRE Digest 245, this gives us quantitative results on how much free moisture is present in a sample and how much hygroscopic salt is present. It is very important to know exactly what is causing suspected rising damp, especially on ancient heritage plasters before any expensive remedial repairs are carried out. BRE Digest 245 is the only way to test for rising dampness, a damp meter is used only as a guide.
We have our own tried and tested methods on reducing hygroscopic salts from walls, this is something we have been carrying for some time now and have had some fantastic results, whilst we can’t guarantee the hygroscopic salts will not come back through the lime plaster, what we can guarantee is this method makes a tremendous difference on reducing hygroscopic salts migrating through the lime plaster in the future. In the first instance a full profile needs to be carried out using the BRE Digest 245 method, then we can see exactly where the salt band is and what type of hygroscopic salt is present and how much.
We have a range of cameras from drain cameras, boroscopes, sub floor ventilation cameras, a radio controlled buggy with a camera for sub floor inspections, remote void monitoring for drying down of timbers, and even a telescopic camera pole that extends to roof level, this can produce a video or images of areas that can’t be seen from ground level.
Many of the repairs that have normally been carried out to listed heritage buildings have been using modern methods that are not sympathetic with how they were originally constructed.
Take hard cement pointing for an example, hard cement pointing on a timber frame is the kiss of death, the cement traps the moisture against the timbers and decay starts, with the decay comes beetle infestation (woodworm) which is normally deathwatch beetle (xestobium rufovilosum).
External cement render
External cement rendering that has deteriorated and cracked allows penetrating dampness to enter the building fabric. Once this happens timbers are at risk of fungal decay and woodworm infestation. South facing elevations are more prone to thermal movement-expansion and are more likely to crack, lime render is more flexible and is less likely to crack and will move with the building as it heats up and cools down.
Internal lime plastering
Lime plastering internally is carried out with a scat coat, or harled coat, a haired coat to give it strength, a float coat to flatten the wall, which is then finished with a lime putty finish plastering coat. Lath and plaster ceilings can replaced or repaired as necessary if they have dropped or are suffering from decay or infestation.
The job of the lime mortar pointing is when the wall gets damp the moisture evaporates out of the lime mortar bed.
This is sacrificial to the stone or brick, this means that over the years it weathers and when it needs to be replaced it is on a like for like basis.
Hard cement pointing traps the moisture, in winter the water freezes and expands which then causes spalling of bricks and stone over a period of time. We now have a bigger problem, because not only does the cement pointing need replacing so does the stone or bricks which is very costly.
Timber decay and woodworm infestation
Long term dampness will eventually lead to fungal decay and woodworm.
In the first instance a survey is needed to find the cause of the problem, this is rectified and drying of the structure is recommended, before any remedial works are carried out.
We also use dry rot search dogs, the search dogs we use are from Envirodogs, we use these to locate dry rot (Serpula Lacrymans), and also the extent of dry rot outbreak.
We also use the dry rot search dog on pre-purchase surveys where a non-destructive survey is needed, this method is especially useful on timber frames or where a property has had a long term dampness problem.
We have been instrumental on helping with the initial training of the dogs and providing samples of dry rot and have formed a close working relationship where we have surveyed the prestigious Bath Abbey and Devizes Castle with envirodogs www.envirodogs.co.uk.
Most plastic paints if you read on the tin read breathable, but how much? Are they really?
The problem we have is when the building moves through the seasons, or through thermal expansion cracks appear which may be very small, come winter when we have wind driven rain this moisture now enters the building fabric and is trapped behind the plastic paint. The wall is suffering from penetrating damp through the winter months and then spring comes and a decorator scrapes the cracks, fills and re-paints with another plastic paint.
This wall would most definitely have not dried down, this is why the paint continues to bubble and cracks again when the building moves again through the seasons and thermal expansion.
Ideally plastic paints should be removed and allow evaporation from the sun and wind, this is how a building dries down.
Plastic paint removal
We have a range of methods for removing plastic paints from stone and red brick. To remove the plastic paint we use patented equipment ranging from low pressure to high pressure hot water systems that may have to include paint softeners if necessary, or where a cement slurry has been used mostly before sandex has been applied, we use aluminium sterate along with water, this is very low abrasion technique rather the just simply sand blasting with grit.
These methods are sympathetic and don’t damage the fabric of the building.
If the building is to be repainted we would recommend a traditional lime wash or Kiem mineral based paints www.kiempaints.co.uk
Lowering ground levels
Is a simple yet effective way of reducing rising damp. This allows greater evaporation at low level which is essential on controlling the height of rise. Ideally external levels are lowered 150mm below the damp proof course or internal solid floors, if the walls are suffering from salt contamination simply reducing the external levels will not stop visible problems to the wall.
Lots of our projects involve heritage work on listed buildings. We carry out lime rendering, lime plastering and lime re-pointing mostly around Trowbridge, Devizes, Chippenham, Frome, Bath, we cover Wiltshire and Somerset-the South West.
Our plasterers are fully qualified and experienced in modern and traditional lime plastering.
Contact Complete Preservation, for lime rendering, lime plastering, lath and plaster work and lime re-pointing.