Old buildings speak a language of their own. Here, we address the common curiosities, misconceptions, and vital truths about living in a piece of Cornish history.
Imagine wearing a plastic bag while running a marathon. That is what Portland cement does to a pre-1919 solid stone wall. Older buildings have no damp-proof courses or cavity voids; they manage water by absorbing it and exhaling it back out. Cement is totally impervious. When rain hits it, the water gets trapped behind the cement face. Seeking the path of least resistance, the water travels inward, blowing your interior plaster and rotting your timbers. Traditional lime is vapor permeable—it lets the building breathe.
A scantle roof is the quintessential historic Cornish roof. Unlike modern roofs that use uniform slates and nails, a scantle roof uses randomly sized Delabole slates (often small and rugged). These slates are "wet bedded" into a thick lime mortar (the "porridge") and hung over the roof battens using small, hand-cleft wooden pegs (usually oak or deal). This heavy, interlocking matrix was specifically designed to stop the violent Atlantic winds from ripping the slates off.
Yes. If your property is Grade II listed, replacing traditional lime mortar with modern cement is considered a damaging alteration and is a criminal offense. Even replacing lime with lime may require consent if the finish, aggregate, or profile changes the historic character of the building. We always advise consulting with your local Conservation Officer, and we handle the technical specifications to ensure compliance.
Absolutely not. Cob is a living, breathing matrix of clay subsoil and straw. Filling a crack with modern poly-filla or cement will cause localized stress points, trapping moisture and accelerating the collapse of the wall. Cob must be patched and stitched using identical subsoil, allowing the new earth to bond naturally with the old.