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 www.environment-agency.gov.uk 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 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.