Building Control Officers & Lime Mortars
Q Has anyone persuaded BCO’s who insist on adding waterproofer to re-pointing (such as Sika1) that this is unwise in a stone/lime mortar building? We are currently restoring/ converting a granite random stone/lime mortar stable block. Because it has change of use dated 2003 then the Building Regs for that date apply, currently the BCO is insisting on waterproofing the pointing and using the dreaded Portland cement, which will create huge condensation problems internally. Is there any written advice I can point him towards other than the English Heritage guidance on Part L that may persuade him this is NOT a Good Idea? The building is not listed and not in a conservation area nor is it noted as being of specific architectural interest so the BCO just views it like any other re-build. We intend to re-point with an H2 hydraulic lime but the BCO won’t agree to this.
A It sounds like you are dealing with a BCO who simply doesn’t understand the materials as well as you do. It is often helpful to arrange a meeting on site between the BCO and the materials supplier you propose in order to allow them to discuss the matter between them. The BCO is more likely to accept their advice/information about their product directly than through somebody who is not obviously an expert. BCO’s do have to deal with some real fools sometimes, and he probably needs reassurance that you know what you are talking about. Although your building is not listed or in a conservation area, it might be worth talking to your local conservation officer too, who may well be aware of very similar work carried out locally, and should know the issues. Failing that, you may have to pay for expert advice from a consultant (who is often a supplier anyway in this instance!), but I would hope that is not actually necessary. It’s worth fighting your corner, as you are right about the bad effects of the BCO’s proposals. Take it up to his superior if you have to! Don’t be tempted to use too weak a hydraulic lime, though: granite is mechanically and physically strong, and effectively impervious, but can be degraded chemically by too much free lime, which turns the mica (I think: or is it the feldspar?) slowly into kaolin. A long-term problem, and perhaps not all that significant, but worth bearing in mind all the same.
A A building control officer has no legal right to request this kind of information. Building control remit does not extend to items as basic as pointing repairs. The BS on masonry is full of information about the correct types of materials to use for new construction and they clearly state the most appropriate mortars for various types of materials, they also show the higher the free lime content of a cement mix the more effective they are in excluding rain from buildings, that’s just and aside, tell the Building Control officer to show the client his remit and where it states they have any jurisdiction in this matter, they don’t.