How Do You Repair a Window Sill?

Window SillSome homeowners will need to know how to repair a window sill, since rotting wood is sometimes a problem for those whose homes have wooden window frames. Since the frames of wooden windows are typically exposed to the elements outside, particularly moisture, the wood may eventually rot, according to This Old House. It’s best to repair the sill before it can spread and cause damage to the entire window frame.

Why Window Sillls Fail

Window seals can sometimes break down due to the following:

• The buildup of pressure between glass window panes on hot days (known as ‘heat pumping’)
• Contraction and expansion of sealant material
• Shrinking and contracting during the cold season

Usually, windows sillls facing west or south deteriorate more often since they’re more exposed to the sun. Excessive direct sunlight will weaken the original window sealing material much more quickly than those windows that face other directions. If you’re thinking about buying new windows, it’s best to choose ones with long-term, transferable warranties since the windows will perform better and a warranty will also add considerable resale value as well.

Don’t Ignore Your Rotting Window Sills

Unfortunately, you may discover that one or more of your wooden window sills has rotted, according to Houzz. Not only will you need to replace it because it looks shoddy, but also because it will inevitably disintegrate in time and cause more problems for your home. It may seem a bit challenging, but repairing or replacing a window sill really isn’t as difficult as most people think. Here are the steps on how to repair a window sill:

Inspect the Damage of the Rotting Wood

Before you get to work on your window sill, be sure that it’s not beyond repair. Check to see how much damage the frame has suffered. If the rot covers more than ten percent overall, then it’s probably best to go ahead and replace it with a brand new one. Keep in mind that some smaller areas of rot can easily be repaired with epoxy products.

Take Your Measurements

First, take measurements of your old sill including the width, depth, and length. Find a suitable piece of wood and then cut it to size.

Access the Window Sill

In order to properly take out the rotting window sill, you need to have access to it. Start by removing the trim on the casing and the channels of the sash. You’ll likely need to use a pry bar in order to do this step. Work slowly and carefully to ensure that you don’t accidentally harm any nearby wood using the pry bar.

Once you remove all the trim, use a pair of pliers to pull out all the nails. When this task is done, check the window jam along with the walls for any other nails and pull them out as well. At this point, you should have full access to the sill. Be very careful removing it. If possible, try to keep it together in one piece, which may be quite difficult if the wood is crumbling due to rot. However, by doing so, you’ll have a cleaner template to install your new sill.

Making the Cuts for a New Window Sill.

If you were able to keep your previous window sill somewhat intact, then you can just trace your design onto your fresh wood piece. If this isn’t possible, take measurements and try to rebuild it as close as you can. Once this step is complete, mark the measurements onto the new sill. Next, carefully cut out the shape of the sill using a saber saw. To get the finest cut possible, it’s best to use a fine-tooth blade. Sand down the entire area so it’s smooth once you’re done cutting.

Fit the Window Sill.

Put your new sill in place and hold it there using a couple of finish nails. The next step is to refit the trim, putting everything back in reverse from the way you removed it. Simply use a few nails to secure each part until you’re sure you have a good fit. Finish the task by using more nails to properly secure both the sill and trim, all of which need to be countersunk. Use wood putty to fill all the nail holes. After it’s dry, sand the area down so it’s flush with the wood.

The last step is to sand down the wood trim and thoroughly wipe it using a tack cloth in order to get rid of the sawdust. To seal the wood, use a quality stain of your choice. Finish up using a wood sealer over the stain where the sill is exposed to the environment for best results. Learning how to repair a window sill is one task that virtually every homeowner can do.

Related Resource: Repair a Window Screen