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Wood Preservaion

Woodworm, Dry Rot and Rising Damp

The first job we needed to tackle once we had bought the house was remedy the damp problem that had been left unchecked for what appeared to be many years. The survey by a local wood preservation expert had revealed problems and we had got a reduction in the price of the property to reflect the costs of putting right the damp proofing and getting rid of the woodworm and rising damp. As well as evidence of damp in the walls, one corner of the living room floor was very springy which didn't bode well. We called in a local wood preservation specialist firm which had been recommended to us by the Estate Agent who we had bought the house through. This proved to be a big mistake (as I will reveal). Their initial survey highlighted several problems such as damp in the external walls, inefficient air bricks and woodworm in the floors. The “specialists” got to work lifting a few boards in the downstairs room ready to spray the woodworm treatment, but the more boards that full extent of the problem was revealed - as well as rising damp and woodworm we found dry rot. My original intention had been, on completion of the damp proof work, to sand and varnish the original Victorian floorboards to make a nice natural wooden floor in the living room and dining room as they had a lot of character, but once all the rotten and woodworm riddled floorboards had been removed there wasn’t much floor left! We then discovered that as well as the floorboards, the joists and some of the plates had been effected by woodworm or damp. Lifting up the floorboards in the dining room revealed that the under floor cavity was full of rubble and builders debris that looked like it had been there for decades. This, of course, was allowing damp to penetrate the damp proof course and stopping air flow under the floor as all the air bricks had been obstructed. So an afternoon was spent scooping out all of this debris - every last bit of it, about 30 full bucket’s worth in total! I started to get suspicious of the damp proof specialist I'd hired the day they sprayed the boards to prevent further woodworm infestation. Although I'd seen many floorboards being lifted downstairs I could not see any signs of this having occurred upstairs. The boards were packed quite tightly in some rooms so you would expect to see evidence of crowbars or similar having been used on these boards - even new nails being used to replace the floorboards, but none were visible. The next job the damp proof specialist carried out was hacking away all the plaster on the all the external walls to a height of 3 feet. Once the new damp proof course had been completed (by chemical injection) these would be replastered again. The injection of a chemical to form a damp proof course was my second cause for concern. This method involves drilling rows of holes at about 15cm (6 inches) above external ground level and above the old DPC but below internal floorboard level (or, if you have solid concrete floors internally the new damp proof course need to be just above these). The holes need to be approximately 18 to 25mm in diameter (or 3/4 to 1 inch) and no smaller than the nozzles of the machine used to inject the walls. Drill holes at 112mm intervals (4 and a half inches) ideally from both sides of the wall. You can hire an injection pump from your local tool hire shop and they will supply you with all the necessary equipment you need. The chemical (usually silicone based) needs to be injected until you can see it wetting the surface of the wall. At the time I had little understanding of the whole process, but I was concerned when I noticed the back wall of the house had not been drilled and some of the holes that had been drilled and injected with the chemical damp proof course had not bee plugged. I had words with the owner of the damp proof specialist firm carrying out the job and he made his excuses before getting the job completed properly. The next problem with the contractors was with the air bricks. After their initial survey they recommended we insert more airbricks around the perimeter of the house to allow better air circulation under the floors and had given us a diagram of where these would be placed. After being told the agreed work on the property was completely done I inspected the work only to discover airbricks that hadn't been cemented in place, missing airbricks where the diagram said they should be placed and, worst of all, air bricks place at a level above the internal wooden floors (you could see this from inside the house as the skirting boards had been removed). We took photos of the shoddy work as evidence as I felt we might have trouble on our hands. Luckily we hadn't paid out for the work at this point so I arranged another meeting with the owner of the damp proof specialists company to confront him with my evidence. Again, he was full of excuses until I showed him the quality of his staff’s work and made it clear that I had photographic and video evidence and was prepared to take matters further he agreed to put everything right (including redoing the woodworm treatment from scratch) and I was invited to witness the work being carried out. To remedy the problem of the air bricks being set too high it was agreed that a trench would be dug around the external walls as the ground level had been increased over the years - this trench would be filled with gravel and would allow the air bricks to be set at a lower level. Finally the job was finished and we were satisfied. It was only a few weeks later relaying the story of our damp proofing problems that we discovered friends of ours had had a similar shoddy job done by the same damp proofing contractor. So the lesson there is ideally getting word of mouth recommendations of trustworthy damp proof specialists from friends or family.

Rising Damp

Rising damp occurs when water is absorbed from the ground into the walls and flooring of a house. The majority of houses have a damp proof course or damp proof membrane built into the walls which acts as a barrier preventing water from being absorbed above it's level. Problems can occur when the damp proof course or damp proof membrane deteriorates and water is allowed to permeate above it. Rising damp needs to be completely remedied or it can lead to further damage to your property. Rising damp can occur when the house was built without a DPC (damp proof course) or DPM (damp proof membrane). The lack of damp proof course or damp proof membrane allows water to be soaked up from the ground. Damaged or perforated damp proof course or damp proof membrane can also lead to rising damp. If the DPC or DPM has been placed to low rain could potentially splash above the damp proof course or damp proof membrane level ans soak the walls. The DPC or DPM should be placed no lower than 6 inches or 15cm above ground level. Another problem is a bridged damp proof course or damp proof membrane - this occurs when external rendering is continued below the DPC or DPM level or if debris has fallen within cavity walls. Debris against external walls can also bridge a DPC or DPM - for example piles of earth, rubbish, building materials. If your damp proof course or damp proof membrane has been placed too low you can remedy the situation by digging a 6 inch or 15cm wide trench around the external wall and fill it with gravel which will allow water to drain away quickly. Bridged DPC or DPM can be remedied by either removing external rendering to expose the damp proof course or damp proof membrane and then remove several bricks to allow access to the cavity where you can remove any debris. If your DPC or DPM has deteriorated the only reliable option is to replace it entirely. There are two options here, either fix the problem yourself via chemical injection or hire a professional company to carry out the procedure. The latter option may be more expensive initially but in the long run it can prove to be the wisest choice as the job will probably be done more thoroughly and to a higher standard. Be sure to hire a reputable company - word of mouth recommendations from friends or relatives would save a lot of searching. Ideally they should be members of an association such as the British Wood Preserving and Damp-proofing Association (BWPDA) as their contractors have to adhere to a strict code of practice and are tested on their skills and knowledge. The BWPDA is Europe's largest association of it type and is an authority on damp. The BWPDA web site can also help you to find a member in your area to give professional advice or carry out repairs. Also ensure that as well as offering a 25 or 30 year guarantee from the firm carrying out the work it’s vital to get a back up guarantee covered by insurance in case the company ceases trading at any point in the future.

Dry Rot

Timbers infected with dry rot (Serpula lacrymans) are dull brown in appearance, very brittle with many cracks and have a musty, fungal like smell. They will crumble easily. Dry rot can spread extremely quickly and, unless treatled quickly, can cause extensive decay. It occurs in badly ventilated spaces indoors where the timbers contain less moisture than wet rot - dry rot is rarely found where timbers are well ventilated. It can spread through wood and masonry via fine tubules that have a white or light grey appearance and is often seen with white fluffy growths called mycelium. Dry rot should be dealt with swiftly and, unless confined to a small area, should be carried out by a wood preservation specialist. All timbers infected with dry rot must be replaced and the source of the problem eliminated.

Woodworm

Several insects come under the banner of woodworm, one of the most common being the furniture beetle - abrown insect that's about 3mm long when fully grown. The larvae of the furniture beetle causes the damage as it feeds on most timber found in the home. the furniture beetle lays eggs in cracks and crevices of wood in the early summer months. When the eggs hatch the grubs will burrow into the timber and can remain there for up to three years, pupating below the surface. When they become adults they will eat their way out of the wood leaving a hole. Less serious woodworm infestation can be treated by treatments that can be found in your local DIY shop, but it is wise to get any infestation surveyed by a wood preservation specialist who can advise on the extent of the problem and carry out the treatment on the woodworm infected timber with a 30 year guarantee. If woodworm infestation is evident in structural timbers hire a specialist contractor to carry out the treatment. If you opt to treat the woodworm yourself always carefully follow the manufacturers instructions and wear suitable protective clothing, goggles, gloves and respirator. Other types of woodworm include the deathwatch beetle, the house longhorn beetle and the weevil. If you suspect infestation by deathwatch beetle or house longhorn beetle contact your local Environmental Health Department.

BWPDA - British Wood Preserving and Damp Proofing Association

The British Wood Preserving and Damp Proofing Association (BWPDA) is the premier trade body for the British timber and building preservation industry. The BWPDA website contains information on damp, timber decay, fire protection, information on members and their services and lists of members.