The wood shrinks, darkens and cracks in a ‘cuboidal manner (typical ‘brown’ rot damage) A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow colouration develops under less humid conditions. This ‘skin’ can be peeled like a mushroom. White fluffy cotton wool-like mycelium develops under humid conditions: ‘teardrops’ may develop on the growth. Strands develop in the mycelium; these are brittle when dry, and crack on bending. Fruiting bodies are a soft fleshy pancake or bracket with an orange. ochre surface: the surface has wide pores. Rust red coloured spore dust frequently seen around fruiting bodies and active decay produces a musty smell.
The wood destroying fungus, Serpula lacrymans, is commonly known as dry rot. However, the name ‘dry rot’ might be considered rather inappropriate since like all wood destroying fungi it requires water for germination, growth and survival. Indeed, water/dampness is the fundamental need of all wood destroying fungi plus, of course, a food source (wood); without either the fungus ceases to grow and dies.
Cavity wall constructions originally began in the 19th century, but became more common around the 1900’s. The main purpose for building cavity wall type constructions, is to allow the inner wall to remain at a constant temperature whilst at the same time protecting it from the elements of nature.
Original build wall ties were manufactured from a wide range of materials including stone, slate, brick, terracotta, cast iron, wrought iron, mild steel, copper and more recently stainless steel. The most common wall ties manufactured and used today are mild steel, under BS 1243 they are wire ties (butterfly and double triangle) and strip ties (fish tail). The main drawback with steel ties is that they will eventually corrode.
Cavity wall ties were introduced into the construction of the walls in order to tie the inner and outer leafs of the wall together and to add additional strength and wind resistance to the property walls. On the older cavity walls with thicker internal walls the wall ties were introduced during construction in order to give a higher wind resistance to the outer leaf as well as preventing the outer wall from buckling or failing under high wind loads. With later cavity wall constructed buildings the wall ties were designed and introduced so that they would mutually support and transfer the applied lateral and / or vertical loads through to the foundations of a property. If cavity wall ties do not exist then the outer leaf wall may fail under wind loads causing the inner leaf wall to become unstable under vertical loads.
It is important to remember that the wall ties should be flexible enough to allow for the differential movement that occurs between the inner and outer wall leaves by settling and thermal movement. Differential movement generally decreases with time. Within buildings that are 20 years or more it is generally accepted that future movement will be minimal.
The effects of wall tie failure can usually be seen to the exterior of a property by cracking patterns to the render/brickwork, outward bulging of the walls, upward cambering of sills, sagging of lintels and lifting of roof edges. The internal effects however are not as clearly noticeable, but can still be seen by outward bulging (usually at first floor level), separation of the window reveals (usually at first floor level), vertical cracking (external wall to internal wall junctions), separation of floors (from skirting boards and stair stringers), internal finishes and internal cracking. Upon noticing any of the above symptoms, a qualified surveyor should be instructed to carry out further investigation tests.
• Properties built up to 1930’s were built with unprotected wall ties
• Properties built up to 1945 have an unknown tie life expectancy
• Properties built up to 1964 have an estimated tie life expectancy of 31 – 61 years for strip ties and 15 – 31 years for wire ties
• Properties built up to 1981 have an estimated tie life expectancy of 23 – 46 years for strip ties and 13 – 26 years for wire ties
• The 1986 Survey of English Houses published by H M S O indicated that a total of 11.3 million houses were built between 1919 and 1986, and of these an estimated 906,000 now require repairs to the wall structure
The new cavity wall ties are made from stainless steel and are inserted into the brickwork, through drilled holes, or by removing individual bricks, at set intervals. The new stainless steel wall ties are secured to the inner and outer wall using various methods. The most common methods used are mechanical, cementitious grouting, polyester resin and epoxy resin.
The original cavity wall ties have to be isolated from the outer leaf in order to prevent them from corroding any further and causing more damage. The isolation works are carried out by locating the original wall ties with a specially calibrated metal detector, opening up the mortar joints at the tie location area, and then physically removing or encapsulating the tie ends.
What is Condensation? Air carries water in form of vapour and the warmer the air the more water vapour can be carried. The measurement of the amount of water in the air is called humidity and air with high water content is said to have a high humidity.
Cool air holds less water than warm air; so if very humid warm air-cools down when it comes into contact with a colder surface it must get rid of some of the water it holds. This excess water is deposited on the colder surface and we may see it a drop of liquid water running down a windowpane, for example. We call this condensation.
The water in the air can come from a variety within the home for example;
• Cooking and boiling kettles
• Washing clothes
• Evening breathing; (at night with no ventilation for example)
• Ironing/drying clothes indoors
• Bottled gas heaters
• Baths & showers
All houses will suffer from some condensation from time to time, but server condensation is a very common problem particularly in cold weather and in older houses. As well as water streaming down windows and on the windowsills and walls beneath, water may also collect directly on walls, especially behind large pieces of furniture and curtains. If wood, wallpaper and plaster are badly affected this will become permanently damp and unsightly mould will start to grow (usually the black spot mould ASPERGILLUS NIGER). Over a period of time wood will rot and plaster will become perished.
Condensation always occurs when humid air is cooled before water starts to condense. The more water held in the air, the higher the temperature at which condensation starts, and in very humid conditions condensation will be found even in quite warm surfaces.
Curing severe condensation can be complicated, because it is temperature, humidity and ventilation and also because the source of the water in the air is often unavoidable we cannot usually cut down on things like washing and cooking and definitely not breathing. There are three main areas of attack, and all should be looked at if you have a problem.
Keeping the moisture in the air that you need. How are the effects of condensation treated?
As we have already seen, it’s impossible to stop water getting into the air completely, and indeed medical evidence suggests that high humidity can be beneficial to people with respiratory problem.
It is sensible, though, to keep activities that produce a lot of warm vapour localised, as the areas in a house where steam is produced are usually warm and so condensation will be less than if the humid air spreads to other parts of the house.
Keep internal kitchen and bathroom doors closed when they are not in use as these tend to be the coldest rooms in the house and hold a lot of moist air. If possible dry clothes out doors and use a vent when using a tumble dryer. Avoid forms of heating which produce a lot of water vapour e.g. bottled gas heaters. Use an automatic kettle or whistling kettle. Deal with any other types of damp from which the house suffers – rising damp (damp course failure and penetrating damp black stop mould) will both contribute to condensation and will course damage.
If humid air can be released from a house quickly it will not have time to cause much condensation at all. The key to this is good ventilation near source. When cooking and after bathing open a window or use an extractor fan. Never draft proof a room to the point where there is no air circulating through it, even breathing will then result in condensation and over a period will cause damp and black spot mould. Keep windows open and air circulating this may result in a small loss of heat but the dryer air will also feel more comfortable and will not cause a health risk. Move large items of furniture a little away from the exterior walls so that air can circulate behind them. Investigate blocked up chimneys and make sure there is sufficient ventilation. If a chimney is bricked up without installing an airbrick, condensation can occur inside the chimney and will eventually soak through into the room.
Keep cellars and sub floor areas well ventilated and check periodically that cellar windows are open a little and airbricks are not blocked. If possible ensure that there is two ventilation points so that air can circulate. Leave any internal doors ajar. When insulating a loft space (and especially if it also boarded and claded) leave plenty of space at roof eaves for ventilation. If there is not enough air circulation in a loft condensation can soak the roof timbers and lead to mould and rot attack. Remember that new plaster will take several weeks’ even months to dry out properly and can add to condensation problems if no ventilation is available.
Consider using a dehumidifier where excessive problems are. These suck in the moist air and collect it as water in a container or piping it to a drain. They can usually be hired for short periods of time but are worth investing in. If plastering work has to be done at any time as a result of condensation, be careful not to dry it out quickly as this will result in the plaster cracking and woodwork may start to warp.
Remember condensation will also damage your furniture and fabrics. Except in very wet or cold conditions air will hold a lot of water vapour. It is only when this air is cooled significantly that a problem arises, so keeping heat in a room and eliminating cold surfaced will prevent condensation (but remember that very humid warm air will always find the coolest surface to condense on). Do not let a room get very cold for long periods.
Check unused rooms frequently for condensation and keep them heated a little and ventilated, as even relatively dry air will cause condensation if it is cooled enough. Only use dry sources of heat and keep interior doors closed to keep humid air from the more active parts of the house getting into the unused areas. Insulate to make the most of the heat you have and avoid large heating bills.
An expensive solution to condensation on windows is double-glazing. Sealed units with a sufficiently large air gap will also reduce direct heat loss and should have the added benefit of being completely draft proof. Secondary glazing is cheaper and several DIY methods are available, but if these are not well sealed moist air will get into the gap and condense on the outer window. This can be significantly reduced by putting packets of silica gel crystals into the gap to absorb the moisture from the air (several proprietary products are available on the market).
Very cold walls can be lined with an insulating material (such as thin polystyrene) and then decorated. Cavity wall insulation a more expensive option will give better condensation prevention also insulation lofts and dormer walls will help prevent condensation on ceilings.
If a timber floor is cold seal the gap between the floor boards or lay thick underlay (inspect the floor for rot and wood worm before fastening down a permanent) do not treat the problem by reducing the ventilation to the sub floor of the cellar beneath you will just move the condensation and resulting problems out of sight for a while.
Water pipes and tanks in kitchens and bathrooms can attract lots of condensation which drips of water can fall from the lowest point resembling a leak concentrating damage, lagging with foam tubes or wrapping will prevent this.
First and foremost, do all you can to cure and reduce condensation by following the guidelines given and any work you need to have done as soon as possible to prevent the problem presiding and causing further damage to your property and health. Treat mould and woodwork and walls with proprietary fungicide cleaner or neat house hold bleach and have it checked for plaster damage.
Where condensation is unavoidable as in the bathroom, kitchens and bedrooms while sleeping, keep area well ventilated and use suitable wall covering i.e. washable wallpaper. If the woodwork has been affected badly enough for wet rot for dry rot to attack it should be replaced with extensive specialist treatment to prevent it from reoccurring in other parts of the house.
If the plaster work has become damp or wet behind or throughout it will become perishable and will need re-plastering.
