The Undercroft in the Abbey Buildings has a floor which, to put it mildly, is uneven. Before pressing on and resurfacing the floor however, it was decided to commission a geophysical survey to find out what, if anything, might lie underneath it. The Abbey Buildings stand very close to the river Thames and, in its days as an Abbey, included a brewery – so there may well be a well down there, or parts of the water table.
Abingdon Archaeological Geophysics undertook the work on behalf of The Friends of Abingdon in July 2013. They performed a “twin probe earth resistance” survey which produced the image shown below-right. In their report, Abingdon Archaeological Geophysics described the three areas on the image as follows:
- Area 1 is an area of low resistance. This is near the door and may be caused by rainwater getting in. Other alternatives include the possibility that here we have an area of soil which is filling in a dishing of the floor where it has been worn away although the assumed 0.5 metre reading depth should be underneath any such deposits. It is, of course, possible that there is a large pit there but this is only one of the possible alternatives.
- Areas 2 are areas of high resistance near walls. This could be wide expanded footings or it could be caused by capillary action drawing moisture up the walls and drying the soil adjacent to them. Not all the walls have this to the same extent.
- Area 3 is a small patch of high resistance. This could be rubble filled pit or a filled in well although it seems a bit small for these. It is however near an area of modern concrete which prevented readings from being made and may be associated with it, although the surrounding area of fairly high readings would argue against this.
They pointed out however, that many features “cannot be located by using resistivity” and that “features may well exist which are not visible on this survey”.
So, the source of the wetness is still something of a mystery, but it seems that there is no immediate danger to the structure of the building.