dry rot

Dry Rot or not – that is the question

Is it really necessary to flood your house with all those chemicals?

The term “Dry rot” is used to strike fear into the hearts of building owners. But it’s only a fungus that lives on damp wood. Take the moisture away and there’s no need for nasty chemicals.

Dry rot has been described as “a cancer of buildings”. No prizes for guessing what sort of person would make such a tasteless remark – that’s right, a salesman for a chemical timber treatment company.

Dry rot in brickwork

Q. I have what a few builders call ‘a serious problem, mate’. The problem is I have dry rot on one of my walls (outside wall with a gully). The rot has eaten away my stairs and strands appear to be coming from between the brickwork (I hacked off all the old plaster and mortar) over a certain area. I have taken away all the damaged wood and believe that I have found where the damp is coming from. My problem now is what to do with the wall; should I plasterboard it up or get it rendered and plastered?

A. The key things are to stop the source of moisture ingress – which you appear to have done – and allow the affected area to dry out and ‘breathe’. To this end cement-and-sand renders are usually a bad idea, especially if the house is old and the original plaster was lime-and-sand. Similarly, plasterboarding the area would be a bad idea, as any future problems would be hidden from view. The ideal would be lime plaster to match the original, but if you can’t find anyone to do traditional lime-and-sand plastering then something like Tarmac’s Limelite is a good second choice. Avoid gypsum finishing plasters as they do not perform well in damp conditions.

Dry rot treatment

Q. My local wood treatment company have told me that even though my windows are to be replaced with a set of PVC-U French doors, and the house has a concrete floor, it will still be necessary to treat and replaster the surrounding walls as the dry rot fungus can live in them and spread throughout my house. (The walls are cavity brickwork construction). Can dry rot live in mortar?
A. Dry rot is a fungus that lives on wet wood. If you remove the source of any moisture, and if – as in your case – you have very little wood in the house, then there will be nothing for it to live on. Irrigating brickwork with fungicidal chemicals is an expensive process that involves removal of the existing plaster, and subsequent re-plastering. It is a trick that timber treatment companies have been using for years to extract the maximum amount of money from their customers, but it has no scientific basis, and is a complete waste of money and effort.

Move Over Lineus

(first published in The Independent on Sunday)

OK, hands up those who understand the following Latin phrase – Praestat sero quam nunquam – “Better late than never”.
Don’t worry if you didn’t get it; I only know it myself because I used to have it on my letterhead. Latin’s a dead language these days, only taught in public schools and seminaries. Which makes it all the more strange that the rag-bag of former plasterers and double-glazing salesmen who call themselves timber infestation surveyors are so fond of using it to describe the state of your floorboards. Woodworm, madam? – oh yes, that’s Anobium punctatum, that is, very nasty. And the dry rot under the bath? – Serpula lacrymans, good job you called us in, sir, that’ll spread all over the house, that will.

So these chancers, some of whom have problems stringing together three words in English, pepper their survey reports with Latin, as though they mis-spent their youth hanging around the natural history museum. They do it because it sounds as though they have made a thorough scientific diagnosis, and also because a Latin name sounds like a medical condition, and that justifies the drastic chemical cure they want to sell you.

Woodworm and dry rot are actually best dealt with by traditional building practices – fixing water leaks, providing good ventilation, and making sure the heating works. But most timber treatment “specialists” have only one aim, and that is to peddle chemicals.

Several readers have reported that their homes, having been sprayed with pesticides, are still infested with dry rot. This can only be because the original conditions which allowed the fungus to flourish – namely wet timbers and high humidity – are still present. If this is the case then chemical treatments are pointless; the moisture will eventually dilute them. And in any case, chemical sprays only coat the surface of the timber – I have seen dry rot growing through the centre of a damp, but treated, floor joist.

The name dry rot is unfortunate, as it gives the impression that the fungus grows without water, which is not so. True, it can spread some distance away from its starting point, and thus grow across dry sections of timber and even masonry, but it still needs water at its source – a great deal of water, in fact – so that dry rot is normally caused by leaking rainwater pipes or plumbing leaks. It also needs at least 75 per cent relative humidity – which can only occur where there is no ventilation.

So dry rot thrives in enclosed spaces with water leaks – such as under baths and under timber ground floors. Remove the source of water and increase the ventilation and the fungus cannot survive; it’s as simple as that. And if you take these measures then there is no need for poisonous chemicals.
It would be nice to be able to report that timber treatment firms which belong to the various trade associations offer a more objective service, but unfortunately this is not the case. In my experience they are all after only one thing – to sell chemicals. In fact the surveyors from the more “reputable” firms can often be the worst, because they are driven by performance targets as well as sales commissions – and, of course, they are sent on courses to learn the Latin names. Oh well, as Nero himself might have said, Die dulci fruere. [“Have a nice day” – ed.]