ASK THE EXPERT
Douglas Kent, technical and research director at the Society for the Protection of Ancient Buildings (SPAB), answers your queries Q I believe I should avoid using a non-breathable carpet underlay over a brick floor in my cottage to avoid damp. What is the best material? You are right in thinking that nonbreathable coverings should be avoided on old solid floors. Rubber- or foambacked carpets are inappropriate but many cheaper fabric-backed designs also lack breathability if they are glued rather than woven together. Here, pieces of cut or loop pile are embedded in an adhesive substrate backed with a layer of coarse jute or hessian. Unlike modern buildings that become damp if barriers to moisture are removed, old floors were built without these and suffer from dampness if they are added. Using non-breathable floor coverings will have a similar detrimental effect with an old brick floor as inserting a damp-proof course as a moisture barrier. Moisture will accumulate below and can be displaced laterally to be wicked up the bases of adjoining walls. Try a woven carpet comprising a 80 per cent wool/20 per cent nylon mix laid over a natural colour, natural fibre contract-quality hair/jute underlay. Ideally, use runners or loose-laid carpet with a generous border left uncovered. Q We’re thinking of buying a flint cottage. Are there any issues with flint that we need to be aware of? Flint buildings shouldn’t be unduly problematic if cared for properly. Defects can be linked to the impervious nature of flint, its unwieldy shape and small size. Such characteristics can give rise to poor bonding that may be further weakened by rainwater penetration due to a lack of maintenance. Inappropriate repair methods and materials (such as the use of cement rather than lime mortar) can also contribute to deterioration. Problems range from the displacement of flints to loosely bonded dressings and the detachment of facing flintwork from rubble cores or backings of stone or brick. Where there is doubt over stability of a wall, consult a structural engineer.
If you have a question for Douglas, email it to periodliving@futurenet.com*