Wood rot

Wood rots when it stays damp for a long time. The moisture lets fungi grow inside its fibres and break them down. On wood outside the house this happens mostly where water can't drain away: at the bottom ends of shutters and doors, in joints, at the feet of a pergolaPergolaAn open shade structure in a garden, on a terrace or a roof, made of posts and beams with slats, reeds, fabric or plants on top. It is often made of wood.'s posts, and wherever wood rests on a floor or on soil.

Rotten wood is soft, often darker, gives when you press a screwdriver into it, or comes away in crumbs. It shouldn't be confused with wood that has simply gone greyWeathered (grey) woodThe grey, rough layer wood develops when it is left unprotected in sun and rain. It is surface wear and usually comes off with sanding. or opened fine cracksCrackA split or gap in render, concrete, a wall, a coating or wood. Fine cracks are usually only on the surface; ones that grow, keep reopening or run diagonally need attention. in the sun, which is surface wear and usually comes off with sandingSandingSmoothing a surface with sandpaper or a power sander to remove bumps, loose old paint or gloss, so the new paint or varnish grips well and comes out smooth..

Rot can't be fixed with paint or varnishVarnishA clear or semi-transparent finish for wood that lets the grain show through and protects it from sun, rain and wear., because the decay carries on underneath. The damaged wood has to be cut out and new wood fitted, or, if the damage is extensive, the whole piece replaced. The best prevention is a finish in good condition and, on new or bare wood, a wood preservativeWood preservativeA liquid that soaks into wood and protects it from fungi, rot, woodworm and moisture. It goes on bare wood, usually before varnish or paint..