How to Fix a Rotted Window Frame

Windows that are made from metal or composites pose fewer problems compared to windows made from wood. This is because wood rots if exposed to dampness for a long period or it can become cracked with exposure to the sun. Apart from that, termites are attracted to wood.

Logs that have been under water for years are hauled out of rivers, and yet the wood is usable. However, water that collects in the space between the wooden frames results in wood rotting. Why is that so?

rotten window frame

Rotting of wood takes place due to several types of fungi. While mold and stain fungi can discolor wood, it is decay fungi that is responsible for breaking down the cellular structure of wood causing significant strength loss. This type of fungi secretes enzymes that produce chemical reactions, which in turn result in dissolving some constituents of wood cell walls. Decay fungi need oxygen, some water, moderate temperatures and food (in this case wood) to survive. As soon as these conditions are met, decay fungi thrive. If even one of these constituents is removed fungi won’t thrive. Although we can control moisture inside our homes, it is difficult to keep wood dry outdoors. It is recommended that wood used outdoors is pressure-preservative treated.

Once rot begins, it can quickly spread and before you know it a whole section of the window frame can begin to crumble. There are several ways to repair the frame and make seamless restorations. Here’s how to fix a rotted window frame.

Assessing the damage

It is easy to spot rot – the wood will have large cracks and some of it may have already crumbled. While not all rot is obvious, some might be hiding under your sill behind an outer façade. You have two options in such a case; to remove the entire frame and replace it with a new one, or to cut out only that portion which is affected and then replace it. If the rot is limited to the sill or the outer frame, you can repair it. However, if it has affected the whole window, including the interior casement, you may want to consider replacing the whole window.

Remove the affected rotten wood

Before you start the repairing process, you should remove the rotted wood. You can use a chisel to dislodge the loose rotten wood. Once you have removed it, you can cut the portion that is needed to replace it. You can first cut that portion and then remove the rotted wood.

Now, with the help of a drill, you can remove the old and rusted nails. With that the wood will become loose. Start with taking away the crumbling wood of the sill or the trim where the rot is. You can use a hammer or chisel to remove it.

Removing Rotted Wood

When the rotten wood is completely removed, you need to restore the hardness of the remainder. You can use a wood hardener that can be applied to the affected area. It will leave the wood strong and much harder. You can also soak the entire area with a liquid epoxy ‘consolidant’ that will make the base sturdy enough to put in the filler. Once you have applied the epoxy leave the area for a few minutes to dry. Apply it again and then repeat the process until the wood ceases to absorb it.

The next step will be quite messy. It is advisable to apply tape around the work area so that the clean sides are not affected.

Take a large portion of the wood filler or polyester resin and mix it with a wood hardener (the two come packaged together). It is important that the two are mixed well and to the manufacturer’s specifications. It remains pliable for about fifteen minutes, which is enough time for you to trowel it in and smooth the surface. Once you have packed the mixture nicely into the cavity, smooth it with the help of a wide putty knife. You can remove the tape once the filler has set in the cavity. If you like you can apply a second coat to the area, but smooth that also. Use sandpaper to even out the surface. The resulting surface is hard and durable and free from rot.

It’s time to fix the wood

Cut a piece of new wood matching the size of the affected sill or trim and attach it. If you like you can use additional wood filler to mold facsimiles of the portion that is visible and paint it so that it resembles the original wood. If you are attaching new wood, you need to fix that with the help of nails to the hardened filler. Before you finish with a primer and paint, finish the new wood with the help of a hand plane and sandpaper to match the existing profile. Remember to fill in any gaps between the new and old wood.


Author: John Clax

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