Suitable render mix for a wet garden wall

[Nigel Watts]

We a have a low wall c. 2'6" high between our front garden and the pavement. It is built of brick, capped with York stone in which railings are set, and rendered only on the pavement side. The soil level on the unrendered garden side is up to a foot higher than the pavement.

The render was replaced about 7 or 8 years ago, probably in a weak sand and cement or sand lime and cement mix. This was repaired last autumn by my builder in some unknown, but probably lime-based material. The repaired areas have now swollen up and cracked badly. In these swollen areas the surface of the render is quite hard but underneath it is still soft, which suggests to me it never set and swelled up when we had the snow and frost.

My builder has opined that the underlying cause is the soil level behind, combined with the fact that the back of the wall is not rendered.

I find it hard to believe that no recipe exists for a render robust enough to tolerate the damp conditions. As I do not want to disrupt my front garden by digging soil out nor have a builder trample over it as he rendes the back of the wall, I would appreciate any suggestions. I would prefer a lime based mix but am not too fussed if we have to use cement. I intend to limewash the wall when the repair is complete.

 

[Nigel Watts]

I have just removed most of the the defective render and found that the brickwork behind is in a bad shape. The wall is about six courses high by nine inches thick (the length of a brick), capped with recently renewed (c. 7 yeas ago) York stone into which the railings are set with lead. The top two or three courses are fine but the lower three/four on the pavement side are barely adhered together with most of the mortar gone and many bricks loose and some broken. The unrendered garden side of the wall is fine however and the wall is still stable

I will clearly have to repair the brickwork before I can re-render - something by builder should have done. I am thinking of using a fairly strong hydraulic lime mortar for resetting the bricks, followed by a similar hydraulic lime render.

 

[MdB]

I am thinking of using a fairly strong hydraulic lime mortar for resetting the bricks, followed by a similar hydraulic lime render.

Sounds sensible to me. If the wall is staying damp, a putty based lime isn't going to work.

 

[Nigel Watts]

I started the repair yesterday. Despite giving the appearance of Flemish bond, almost all end on bricks on the pavement side were only half bricks and most of the bricks in the bottom three of about six courses were loose. I managed to remove all the loose bricks without compromising the integrity of the wall which is capped with bath stone and iron railings which were restored about 8 years ago. I then cleaned out the failed mortar and am resetting the original bricks using an NHL 3.5 and sharp sand mortar.

 

[andrew gayton]

you could line the unrendered walling below soil level with cut down plastic coated profiled roof sheeting. The profile would allow air to circulate behind the covered walling to allow it to dry, whilst the overall cover would prevent ongoing saturation from the garden soil.

 

[Nigel Watts]

This is the wall. The picture was taken about half way through the work. On the right you can see the loose bricks. The left hand end has been repaired.

How long should I leave the mortar to set before applying the first render coat?