London Clay

A surveyor that we work with recently came across a situation where a property in the Hammersmith area of London, which had areas of clay, much of it shrinkable London Clay, had a tree in her garden removed some time ago rather than pruned, which is what we generally recommend. This means that the water that the tree's roots were taking away was allowed to soak into the ground. Where there is clay this will cause heave. Please see our other articles with regard to clay.

Many years later the lady in question built an extension on the property and, as is the case, over the years foundations have got deeper and deeper; typically a Victorian house would have had stepped brick foundations, perhaps half a metre deep. In post war we started using concrete foundations of about a metre to a metre 1.2 metres deep. Then more recently, particularly where there's clay or trees nearby, foundations are at least two metres deep or deeper.

In this case the local authority building control officer required these deep foundations (or should we say normal foundations these days), together with a product called Clayboard to accommodate heave. This is where the clay expands and subsidence is normally caused where clay contracts. Both of these are to do with clay's water content.

Clayboard is a relatively new product that we first came across in approximately the late 1980's/early 1990's and this clay takes many forms, from polystyrene to a labyrinth of cardboard with a hardboard finish on either side. The purpose of all the Clayboard is to allow for expansion in the clay, therefore have an expansion gap, so to speak, which will stop heave of the clay affecting the property.

An example of this is Dufaylite Clayboard, which can be seen on dufaylite-clayboard.com . This product shouldn't be confused with clay board, which is literally a board made from clay that is used on the internal of walls.

From what we understand there is an argument between the builder's and building control and no Clayboard was put in. Subsequently there was a problem; the builders had disappeared and building control didn't take any responsibility for this.

Clayboard specifications are very dark science to say the least and you do need an expert to advise on the right thickness of product and right thickness of void. This all depends of course upon the soil conditions and you may even need a soil engineer's report.

This example reminded us of a quite different situation, but where we were still involved with Clayboard problems. We were project managing the building of quite a large multi-occupied residential property in the Ealing area and Clayboard had been specified and had been duly installed and a damp proof membrane added over the top of it. We were not aware of any problems until the lorries from the pour of concrete finished but we still had a need to finish pouring concrete into the slab.

We then did a double check to make sure that we had ordered the right amount of concrete and that they had all arrive, which we had, only to discover that the Clayboard was collapsing during the pouring of the concrete, unfortunately filling the void under the floor with concrete, meaning there was no longer an expansion joint underneath. There was very little that could be done about it at that stage and we spoke to the architect who advised us to order more concrete and fill in the slab, which we duly did.

Now, as a qualified Chartered Building Surveyor, and often wonder what would happen to the site as there were a lot of trees surrounding it and no doubt there will be some heave as some of these were removed during the construction process. Although we did return once we didn't actually have a look to see if there were any problems.

In Summary

If you are building on a clay soil you need to get some expert advice and you also need to make sure the builder carries out the work as specified. We are more than happy to come and supervise such work and prepare expert witness reports or schedules of condition if you have had some work carried out and you believe there is a problem with it.

Independent chartered surveyors

Commercial property surveyors

If you have a commercial property, be it leasehold or freehold, then you may wish to look at our Dilapidations Website at www.DilapsHelp.com and for Disputes go to our Disputes Help site www.DisputesHelp.com .

We hope you found the article of use and if you have any experiences that you feel should be added to this article that would benefit others, or you feel that some of the information that we have put is wrong then please do not hesitate to contact us (we are only human).

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