If you are entrusted with building and property maintenance, as any home owner or building manager is, then the danger of dry rot is one of the most serious dangers you will ever face.
That’s partly because it is insidious. By the time you discover it the chances are that it has already established itself. Whilst initially it needs damp conditions to form, it can then spread silently even in timber, walls and masonry that isn’t particularly damp.
Often the first sign of it is when you discover its spores, which are a bright, rusty red colour and minute in size – about 0.01mm long. They are produced in abundance so as to form a fine, rust-coloured dust not far from the fungus itself.
By this time it can affect several square metres of surface. If this happens to you then you should consider yourself in an all-out war against the fungus. To maintain your property you have to deal with it immediately.
You may have to take up floorboards and pull off wall plaster in order to locate the full extent of the attack. If you are not averse to some DIY you can do this yourself without calling in a builder at this stage.
If there is insufficient ventilation below the floorboards then take the opportunity to improve it. It’s surprising how often the original problem is caused by some debris that is easily removed.
Cut out and remove all decayed wood that shows signs of infection, and go around 18 inches beyond the visible signs of attack to ensure you cover any rot that is hiding beneath the surface. If dry rot is found on the side of a wall, then most likely the other side is affected as well, so check the adjoining room and its woodwork for damage.
Remove wall plaster until there’s no sign left of the fungus. It grows in threads, so watch out for these carefully and bring in professional help if you need it. Collect and safely dispose of all the infected wood and plaster work that you’ve removed.
Thoroughly clean the remaining woodwork, plaster and brickwork. Brush down the surface and remove any loose mortar and pieces of old wood. Apply a high quality fungicide to the brickwork until the surface is saturated, using a large brush or a coarse spray from a low pressure sprayer. Don’t forget to wear a protective facemask and gloves.
Try to avoid bringing new timbers into direct contact with the old brickwork, e.g. by resting the ends of new joists on felt where they enter a wall. Cover the brickwork around window or door openings with a layer of zinc oxychloride plaster or paint where it has contact with new wood frames.
Thoroughly treat all new and existing timbers with a generous coat of wood preservative, and you should have eradicated the dry rot completely.
Because dry rot is such a dangerous and potentially expensive problem it’s vital that you do a most thorough job in getting rid of it. Your building and property maintenance obligations demand nothing less. And whilst a competent amateur can carry out these procedures it may be necessary in dealing with a severe attack to call in the professionals.