19 Apr Hot Mixed Lime Renders
Hot limes continue to be specified regularly for new works in a whole range of applications. Recently, two projects have called for the use of renders produced using the hot lime method. The following paper outlines the works completed and examines the processes undertaken.
As you will note from the attached report, although ‘The New Lime Revival’ is still somewhat in its infancy, we at PAYE have adopted the use of the material across a variety of projects in a number of differing situations and locations. We run regular training days for staff and architects and have over the last 18 months or so completed a number of research papers on the subject. Whilst all projects appear to have been successful to date, we still continue to hold certain reservations and as we have discussed previously, this being principally linked to the lack of proven data published to date.
We would like to think we retain a healthy cynicism to its widespread adoption and still believe each project should be evaluated on an individual basis. Hot lime mixes certainly have their place, but we think that purpose, location and environment should really inform where they are being specified. A number of projects based in salt laden marine environments have for example, recently been proposed. Given that the key to a successful mortar, is how it copes with the transference of moisture and salts, this is a potential risk and we feel duty bound to raise this concern with the project team. Composition of the mortar should certainly be given the same consideration to importance as well as that of the binder, but sometimes this almost seems to be lost in the push to use this ‘new’ technology.
Experience has shown shrinkage to certainly be an issue, particularly when using thick or deeply applied mortars. Cracks can of course be tamped back and brushed out, so being removed during the tending process, but will not always be immediately visible – potentially weakening a bed and opening areas up to ingress not visible to the naked eye.
The other issue we continue to encounter, is an oversight with regard to detailing. Lime is a remarkable medium, but it cannot perform miracles and so design functionality must give it a fighting chance. Mortars that are sky facing or will remain saturated for long periods for example are prone to failure and so should be designed out.
To conclude, care must be given to how this ‘new’ technology is being specified and where it is being used. It is not currently the answer to all conservation conundrums. That said, once the proven data has been published and if this helps to standardise approaches and materials, then we will of course unreservedly join the movement which seems to garner almost evangelical levels of support.