Getting a Home Survey

Getting a home survey, and not just a bank valuation, is essential when buying a property. RICS research shows that on average home buyers spend £5,750 on repair bills once they have moved into their new home. A home survey will provide the buyer with much more information on the state of the property and any work that will need to be carried out.

Flood Risk

flooding property flood gloucestershire stroudIn 2009 the Environment Agency estimated that 1 in 6 (5.2million) properties in England are at risk of flooding in one form or another. This was double the numbers that were previously thought to be at risk. The reason for the increase is that for the first time properties at risk from surface water flooding have been included. The risk from surface water flooding is likely to increase due the rise in the number of unusual weather events brought about by climate change. Some 70% of the damage suffered in the floods of summer 2007 was from surface water.

The losses suffered by insurers will drive up the cost of premiums for those properties deemed at risk. If insurance cover is not available on standard terms it will also make it extremely difficult to get a mortgage. The availability of insurance on ‘normal’ terms and the greater perceived risk of flooding will have an effect on a property’s value.

Whilst information about flooding from rivers and the sea can be easily obtained from the Environment Agency website the flood maps do not include information about other flood risks, including surface water and ground water flooding. However, there are companies that can provide a ‘desktop’ flood search for a modest cost that is dwarfed by the potential losses that could be suffered if the property flooded. If you are buying a house it is better to have this information at an early stage before you incur legal and other costs.

On a positive note steps can be taken to reduce flood risk. This is either in the form of measures to prevent the property flooding or by using materials that allow the building to dry out faster with less permanent damage. Further guidance on this and more can be found on the EA website and via the link below to an RICS guide ‘A Clear Guide to Flooding for Property Owners’.

A Clear Guide to Flooding for Property Owners Download A Clear Guide to Flooding for Property Owners

Japanese Knotweed

japanese knotweed damage surveyor stroudJapanese Knotweed is an invasive perennial plant brought to Britain from Japan between 1825 and 1841. It was originally introduced as an ornamental plant and was favoured by landscapers due to its quick rate of growth forming dense screens.

In the UK it has been prevalent in Wales for some time due to the moist climate but has since spread throughout the UK and is now so widespread that there is not a 6 sq mile area in the country where it is not found. Locally Japanese Knotweed has been found in Nailsworth, Stroud, Eastington and Bussage and is bound to be elsewhere. It is tolerant to adverse habitats such as soil acidity, heavy metal contamination and air pollution meaning it is able to thrive where other plants would fail.

The Government took action on the problem in 1981 when it was included in the Wildlife and Countryside Act 1981and it was made in offence to ‘plant or otherwise cause Japanese Knotweed to grow in the wild’. The disposal of waste containing knotweed is covered by the Environment Protection Act 1990.


The Japanese Knotweed can be identified by its bamboo like stems in a thick central stand of plants. It has oval or heart shaped leaves and produces white flowers during it vigorous growing season from May-October. This growing season is when it can be most readily identified. The flowers and leaves die back during the winter months but leave the stems standing allowing identification to be made if with more difficulty. A guide to identification and further information can be downloaded from this link.


Japanese Knotweed is a massive problem both economically and environmentally in the UK. It is estimated to cost the UK £150 million every year.

Japanese Knotweed has extensive root systems that can stretch, from a well developed stem, 2 metres down and 2 to 3 metres laterally from the plant. A new plant can spread from a fragment of root as small as 0.8 gram making it extremely difficult and labour intensive to remove.

As its growth can outstrip native plant species it can spread quickly across wide areas if not controlled. In environmental terms it provides a poor habitat for native insects, birds and mammals.

Japanese Knotweed can cause severe damage due to the strength of its root system leading to damaged patios, paths, drives, outbuildings, conservatories and other garden structures. Although much damage is aesthetic it can also make structures unstable and dangerous where retaining walls and building foundations are affected. Drains and other buried surfaces can also be damaged. All of these can be very expensive to put right and work cannot be started until the infestation has been fully cleared.

An infestation can make your house unmortgageable. Loan companies are becoming reluctant to lend on properties affected by the invasive weed. Some individual lenders will consider applications where Japanese Knotweed is found by their surveyor but will ask to see evidence of initial treatment of the problem and commitment to fund three to four year treatment programs in advance of lending. Most insurance companies policies do not cover damage caused by Japanese Knotweed and have recently become reluctant to provide cover on properties damaged by an infestation.


Eradication methods are both time consuming and expensive. There are a number of different ways in which this can be carried out.

  • Excavation of the plant and it roots. This may seem a simple and cheap way of removing the weed but ALL of the roots must be removed, which is time consuming and labour intensive. Secondly, all the affected soil must be disposed of correctly which mean paying a specialist contractor.

  • Burial on-site. This avoids the high cost of disposal but the knotweed needs to be covered with 5m or more of overburden or a root barrier installed to prevent regrowth.

  • Chemical treatment. Japanese Knotweed is resistant to most herbicides but can be treated over several seasons (at least three years) with glyphosphate. This is usually the most realistic option and

Lime Mortars Explained (Part 3)

Part Three: Choice of mortar and application.

The usual constituents of mortar are the binder, i.e. lime, and an aggregate in the proportions of one part binder to two or three parts of aggregate. The choice of mixture and aggregate depends on the material to be pointed up. In wider joints, coarser aggregates and galleting (see below) can be used. This helps reduce shrinkage and prevent the mortar cracking. Fine joints should be filled with a stronger mix, up to 1:1, using stone dust as an aggregate.

The type of lime used depends on the situation in which it is to be applied. As well as considering the material to be repaired, the environment in which it needs to perform must also be taken into account. As noted in Part One stone needs to be repaired with a compatible mortar. Oolitic limestone, which incorporates small pores, needs a porous lime mortar made using lime putty. The more open textured weatherstones from the upper limestone beds, known locally as Minchinhampton stone, will be tolerant of a hydraulic lime mortar. Weatherstone is used in the more exposed positions on a building, e.g. parapets, cills and plinths, where a hydraulic lime will perform better than a ‘fat’ lime mortar.

Accelerated setting of lime putty mortars can be achieved by the use of ‘pozzolanic’ materials; this term derives from volcanic ash found in Pozzuoli near Naples in Italy, which was used by the Romans to hasten the setting of lime mortar. Pozzolans include substances such as crushed brick or tile and PFA (Pulverised Fly Ash) which contain silica and alumina. These induce a hydraulic set and produce a stronger mortar with greater resistance to water. When used they typically make up a tenth of the volume of the mortar. The addition of small amounts of cement to lime mortars has been common practice but is not recommended as research has shown that these mortars are prone to failure.

‘Fat’ lime mortars (made with lime putty) should be used externally when there is no risk of frost and ideally in temperatures over 5 degrees centigrade. Low temperatures will inhibit carbonation and in extreme conditions cause the water content to freeze. High temperatures and strong winds can dry out the mortar too quickly. In all conditions, the carbonation process will only take place when the mortar is damp. Before repointing the open joints should be thoroughly wetted. In wide joints wetted stones can be used to pack out the joint (galleting) and reduce the amount of mortar employed. A round ended gauging trowel or similar tool should be used rather than a ‘pointing’ or bricklayers trowel. When filling the joints the mortar needs to pressed firmly in and left slightly proud of the surface. After about 24 hours and as the mortar stiffens it should be pressed back to prevent cracks developing. Following this excess mortar and trowel marks should be removed with a stiff bristle brush; a churn brush is very effective. This also gives the mortar an open texture and consistent appearance. During the carbonation process the mortar should be kept covered for at least two days with dampened sacking or plastic sheeting to reduce evaporation and the work regularly damped down with a water spray. The mortar should be finished flush with the surface of the stone to promote water run off. Ribbon pointing should be avoided as the ledges encourage damp penetration into the stone, see photo 2. The colour of the mortar is also important if only for aesthetic reasons; a light mortar highlights the stone whilst a dark mortar emphasises the pointing, see photo.


Limestone mortar property surveyor stroud pic

Photo 2: Dark cement mortar (Richard Wood Surveying Ltd).

Lime Mortars Explained (Part 2)

Part Two Lime: different varieties explained.

It may seem odd to start an article about lime to talk about cement but it warrants a mention because it is such a marvellous material. The use of Ordinary Portland Cement (OPC) has become widespread throughout the construction industry from the Second World War onwards. A type of cement was used by the Romans to make concrete; this was probably hydraulic lime mixed with material to make it set faster. However, these methods died out with the fall of the Roman Empire and were not rediscovered until the eighteenth century. John Smeaton, an engineer, pioneered the use of hydraulic lime. He built the Eddystone lighthouse 14 miles offshore on rocks submerged at high tide. This needed a mortar that set quickly and was incredibly strong. OPC was developed in the nineteenth century by using a new type of horizontal kiln and firing limestone and certain types of clay at higher temperatures. The cement produced using this method was even stronger and faster setting than its predecessors and could be manufactured to consistent quality standards. These qualities make it easy to use and construction a much quicker process. By contrast lime mortar, particularly lime putty based mortar, is slow to set, relatively weak (especially in the early stages of set), time-consuming to mix and apply and has become difficult to obtain.

Limes and cements set by different processes. The incorporation of clay impurities in the limestone used for cement production imparts a chemical process called a hydraulic set. Pure lime putties set by a process known as carbonation. The latter involves the absorption of carbon dioxide and results in a material that has the same chemical make up as limestone. Carbonation requires the presence of moisture to set properly.

Quicklime is the material produced by burning limestone. It is highly alkaline and caustic and was historically used for disposing of dead bodies. Dry hydrated lime, also known as bag lime (or calcium hydroxide for the technically minded), is made by adding water to quicklime (slaking). The result is a dry powder. The slaking process produces a lot of heat and drives off the water content. It is best practice to leave the mortar made with bag lime to mature in order to allow the lime to absorb water and distribute itself as fine particles around the aggregate. It is considered inferior to lime putty, as it tends to absorb carbon dioxide in the bag and can fully carbonate before use. Lime putty (Hydrated Lime) is a material that has taken the slaking process a stage further and is fully slaked to form a putty-like material. Deprived of carbon dioxide by storage in a sealed container or covered by a layer of water it will remain in this form for many years and is said by many to improve with age. N.B. All putty should be stored for a minimum of 2 weeks before use.

Hydraulic limes have the ability to set without the presence of air, even under water, and combine to a lesser or greater degree both carbonation and a hydraulic set depending on the strength required, which is determined by the class of hydraulic lime used. Hydraulic limes come in three strengths designated by their Natural Hydraulic Lime class, which are NHL 2, NHL 3.5 and NHL 5. The number refers to the material’s compressive strength expressed in N/sq mm and these roughly correspond to the former designations of feebly, moderately and eminently hydraulic. NHL 3.5 is suitable for new construction, whilst NHL 5 is used in more challenging conditions, including sea defence walls, canal walls etc.

On an environmental note, the production of cement involves burning limestone at far higher temperatures than lime with the consequent increase in energy consumption. Moreover, the carbonation process involves the absorption of carbon dioxide.

Lime Mortars Explained (part 1)

Part One. Why use lime mortar?

Mortar has a threefold purpose. It bonds masonry together, ensures that loads are spread evenly and fills the gaps between the bricks or stones. The latter function helps makes the wall weatherproof and thereby excludes damp. This is essential in traditionally built houses with solid walls. Unlike modern cavity or timber-framed walls, which separate the outer and inner layers of the construction, solid walls fulfil their weatherproof function by their ability to absorb and release water.

Limestone is porous; it can absorb large amounts of moisture, for example from driven rain, and in dry conditions needs to release equivalent volumes of water through surface evaporation. Therefore, it is important that the ‘breathability’ of the stone is not inhibited and that the correct type of mortar is used to carry out repairs, including repointing. Dense cement-based mortar severely limits evaporation from the mortar joints and causes moisture retention. Dampness can lead to rot in built-in and internal timbers, frost damage to stonework, poor thermal performance and surface erosion of the stone due to salt crystallisation.

Richard Wood Surveyor stone wall in Stroud

Honeycomb weathering to stone wall in Stroud.

Salts are present in the soil, most historic stone structures were built with earth mortars, and lime mortar, a relatively expensive commodity, was only used at the exposed joints. Moisture will mobilise salts and as evaporation takes place, salts are left behind at the surface (efflorescence), or within the pores as crystals. During crystallisation, the salts expand in volume from their dissolved state. Erosion of the stone can take place when crystallisation occurs inside the stone. In stone with large pores, the crystals can form without causing any damage but finely pored oolitic limestone, such as that commonly found in buildings in the Stroud valleys, is susceptible to this form of weathering.

The combination of hard cement mortars, frost damage and salt crystallisation is the cause of the ‘honeycomb’ weathering illustrated photograph 1. A certain degree of damp is inevitable in stone walls but it is clearly better that the salts crystallise in the mortar, which is easily replaced, rather than the stone. Moisture will tend to move from a dense material into one with higher porosity and evaporation will not take place from a material with impermeable characteristics, i.e. a cement mortar. It is a general principle that the mortar should have greater porosity than the brick or stone with which the wall is built. In this event, the mortar will act as a wick extracting moisture from the masonry. These characteristics needed are met by lime-based mortars.

Sash Windows

English Heritage has recently published the results of research commissioned from Glasgow Caledonian University into the thermal performance of sash windows. Sash windows became fashionable at the end of the seventeenth century and there are many surviving examples from this period, Georgian and Victorian times. They have proven durability and enhance the appearance of traditional buildings. Their durability is in stark contrast to modern windows, many of which are designed to have shorter lives, typically 20 years.

Part of the pressure to replace sash windows comes from the need to improve the thermal performance of existing buildings in order to reduce carbon emissions and heating bills. Traditional sash windows are seen as performing poorly and replacement is advocated to improve insulation standards when refurbishment is carried out. The research was undertaken to establish the true performance of sash windows and measure how improvements, such as draught-proofing and secondary glazing, reduce heat loss.

Heat loss is expressed as a U-value, the lower the figure the lower the heat loss. Current Building Regulations require windows to have a U-value of 2.0. An unimproved sash was measured to have a performance of 5.3. By fitting secondary glazing with low-e glass and shutters, heat loss could be reduced by 62% resulting in a U-value of 1.6. Even simple low cost measures can result in substantial reductions in heat loss. Heating is most needed in the shorter days of winter and most of us are out at work during the day. The use of well-fitting shutters, heavy curtains or roller blinds in the evenings can reduce heat loss by 40 to 60%.

The U-value is only a measure of loss through conduction, sash windows are notoriously draughty and considerable heat loss can occur through ‘air leakage’. By merely overhauling and repairing the sashes heat loss caused by draughts can be cut by 34%. Professional draught-proofing can cut leakage from 183 cubic metres of air per hour (unimproved) to 26 cubic metres per hour. Fitting secondary glazing can cut this figure to 8 cubic metres per hour and provide performance that betters standard modern windows.

The research concluded that simple measures, such as fitting blinds or heavy curtains, can achieve major improvements in U-values, draught-proofing can reduce air leakage to a standard at or below that of modern windows fitted with trickle vents, and that further improvements with secondary glazing will give good performance during the day and better still in the evenings when used in conjunction with curtains, blinds or shutters.

Source: Research into the Thermal Performance of Traditional Windows: Sash Windows. Executive Summary. October 2009. English Heritage Research Report