Typical Defects Encountered
Figures 3 and 4 show a range of defects that earth walled buildings can suffer.  Some of these are due to a lack of maintenance.  A number may be due to modifications to the building, some of which may have taken place during the 19th century or earlier.  For example, increasing the headroom of the first floor can be potentially damaging through either reducing the lateral restraint within the roof structure and causing spreading of the walls, or increasing the height of the walls in a different material, leaving it more exposed to the weather through a reduced eaves overhang.  Almost certainly the main cause of failure in earth walling is the presence of excess moisture, particularly at the base.  Such failures can be sudden and dramatic, probably accounting for the common perception that earth walling is an inferior construction.

FIGURE 3:  TYPICAL END ELEVATION OF A COB DWELLING

 5.A near vertical crack in this position (or at a similar distance from the corner on the odjoining elevation) may be due to lateral thrust from the roof However, it may have started soon after construction as a result of drying shrinkage, and worsened subsequently through weathering.  Having eliminated the causes of such cracking, the walls con be stitched across the crocks using material closely matching the original.  Techniques for this are referred to later.  Removing forge areas of earth walling and replacing it with brickwork or blockwork is unlikely to be necessary or indeed a suitable solution.  Such an approach can compound the problem through introducing tensions at the interface between the different materials.

7Vegetation can be damaging, with roots penetrating and displacing the earth walling. Also, bees con cause severe pitting of the surface
1 .Moisture con find its way into the walls if the roof covering and Poshings are not adequately maintained, if the eaves overhang in insufficient, or if gutters and downpipes (where needed) are neglected
2. Cracks in the external render will allow water ingress.  Do not repair cracks or replace rendering with strong cement based renders, but instead use a lime render matching the original as closely as possible.  Avoid using mesh, such as chicken wire or expanded metal, in renders as these ore not necessary if the work is done properly.  Where in the post such reinforcing methods hove been used in combination with rich cement renders, additional problems almost inevitably result
3. Hollowing of the wolfing surface con occur, commonly at the base, through excessive splashback, or through cattle rubbing or licking. Holes near the base of the wailing may be an indication thot rats have burrowed into the walls, and this con result in a considerable network of tunnels
8.The ground level should be well below the top of the underpin course, preferably at least 15Omm. In many cases, over the years the ground level has built up to an unacceptable level. Care must be taken when remedying this situation to ensure that the foundation remains adequately covered. Each case needs to be assessed on its own merits.
4.The render and the coating (ifany) applied to it should enable the wall to retain its breathing qualities. Limewash was the traditionally applied coating, and it is questionable whether as yet there ore any modern coatings which con match its suitability for earth welled buildings, or, indeed, for other forms of traditional walling where the ability to breathe is a key requirement. 9.If the ground around the building is excessively damp and this appears to be adversely affecting the Poor and walls, some form of ground treatment may be appropriate.  This needs to be carefully designed to ensure thot drainage trenches and possible shrinkage through drying of the ground do not threaten the stability of the foundations.