There are two ways that you can deal with rotten wood, either cut the rot out and replace it with new wood or use a chemical wood hardener kit. Doors, windows and frames are the most common places to find rotten wood, where rain has got in through damaged paintwork. It can also be found in internal timbers, in ceilings, walls and floors, if rain has got in or if there is a leak in the plumbing system.
Rotten wood should not be confused with dry rot as it should be treated very differently. Dry rot is a fungus that can spread and do a lot of damage to a home so if you are not sure what you are looking at get an expert in to check it out.
Replacing Rotten Timber
Cut away all the rotten wood using a craft knife and a chisel, cutting back until you get to the good wood under or behind the rot. Don’t be tempted to leave any rotten wood behind, it will just mean that you have to do the job all over again in a year or two. Tidy the resulting hole up as much as possible to give straight edges for a replacement section to mate with. If possible, cut the ends of the recess at 45 degrees; that will make it easier to get the new piece to fit.
Measure and cut replacement timber that will slot into the hole. Drill holes for screws and countersink the tops so that the heads will disappear below the surface of the new wood. Don’t use nails, you need to be able to draw the new piece into the recess you’ve cut, and tightening the screws will do this.
Blending the Repair In
Before you put the new piece of wood in paint it and the recess with wood preservative and wait for it to dry. Apply glue to the sides of the recess and the new wood, clamp it into place and wait for that to dry. Then put the screws in, tighten them and hide the heads with either a plug of wood or some wood filler.
Finally sand down and paint or varnish the whole area. Use good wood primer and then two coats of gloss if you are painting or two or three coats of clear varnish.
Method Two: Wood Hardener
If that’s all a bit out of your carpentry comfort zone there are a number of kits products on the market for dealing with rotten wood. These products will solidify and strengthen rotten wood so that it can then be repainted.
Most of these products have wood preservative pellets which are inserted into holes drilled into the bad timber and a liquid wood hardener that’s painted on. Then there may also be a high performance wood filler that can be used to build up areas where rotten wood has fallen away or been removed. They all work in slightly different ways though, so follow the manufacturer’s instructions to the letter.
Using a Wood Hardener Kit
Usually you will need to remove the worst of the rotten wood, though there’s no need to go right back to good wood. With some wood hardener products you may then need to dry out the area with a heat gun before inserting the pellets and painting the area with the wood hardener. You may need to wait some time for this to dry before continuing, sometime a whole day.
Then build up the area with wood filler, bringing the wood back to its original profile. Once this has dried you can sand it down to make a smooth transition between the good wood and filler and paint the whole area.
Wood Hardener and Varnish
Note that because of the colour of the wood filler you are unlikely to get good results on an area that needs to be finished with clear varnish rather than paint. It will not look good if sections of filler show through next to the wood. For this reason the traditional method of cutting away the rot and replacing the wood is the best option if you are dealing with a clear varnish finish.