How to Repair Rotted Window Frame: The Full Guide

Windows are some of the most important features in a house. Wooden frames often fall prey to wood rot though. Even though this hurts the integrity of the window, it can be a pretty easy fix. This guide will be a step-by-step of how to repair rotted window frames.

1. Identify The Rot

Wood rot in general is pretty obvious. It’s characterized by wood being soft and flaky. It falls apart easily. This means that even if your wood rot is beneath a coat of paint, you should notice it without any trouble. This is because the paint will likely have flaked away with bits of wood. Leaving holes of exposed wood.

With that in mind, having obvious holes in your wood and paint is not always the case. Sometimes the paint may be just fine and will require a more intense inspection.

Two key signs that your wood is rotting are the color of the paint and the feel of the wood.

If your paint is starting to discolor then it is a good indicator that you don’t only have wood rot, but also mold. This is a serious problem and should be handled immediately.

There are a couple of caveats to that rule. For example, if the wood is on a deck. In this case, the discoloration could also be sun bleach or simple wear and tear. This would require a physical examination.

The feel of the wood is always a dead giveaway to the health of the wood. If the wood is flaky, spongy, or extra soft, you’ve got rot. You can tell all of these by touching the wood or trying to hurt the wood with your hands. If the wood is healthy then there is very little your hands could do to hurt it.

To examine, push on the wood with a couple of fingers and see what happens. If nothing happens and you still need convincing that your wood is good, grab a firm hold of the wood and try to break it. If your wood breaks easily then you got a problem.

Do not exert more than minimal strength when trying this. If your wood is rotted you should have no problem breaking it.

2. Removal Of The Wood Rot

Removing wood rot is pretty straightforward. All you need to do is get rid of it. You might be asking how. Fear not, here are a few ideas.

If you are leaving your window in while repairing wood rot then using a router and wood chisel (a flat head screw will work too, it’ll be harder though) will be easiest. You could also use a saw to remove large chunks that stick out.

Using a router will be easiest with a V-shaped bit. Since the wood is rotted through any grinding bit will work okay. You need to get rid of all rotted and softwood before you start repairing the frame.

If you leave rotted wood in a frame then a proper seal can’t be achieved, meaning your boards will rot faster than otherwise. Leaving rot in your wood will also damage your boards fast because rot spreads even if it is perfectly sealed out from any water.

You will need to use a chisel to remove any hard to reach wood.

3. Finding The Right Fix

Knowing what kind of repair you need to make is key to ensuring a lasting repair. There are three types of repairs, and each of them has its challenges and advantages.

Whole Wood Repairs

I use the term whole wood repair about how much of the board you will be removing. So, a whole wood repair is one that requires the removal of at least one whole board.

You would perform a whole wood repair when you want to make sure you get all the rot. This is the hardest and most expensive repair. It will ensure the rot is gone though.

Before you attempt this there are few window basics you need to know. Any part of the window frame could have rotted. Rot often occurs in the cill, bottom rail, and bottom corners of the frame.

Whole wood repairs have two types of names. A full-frame and an insert.

A full-frame replacement will replace all the wood components of your window and frame. This is best if you have a lot of rot. It is the most pricy though.

If you want to do this it’ll be a lot of work and I recommend hiring someone to do it. It is doable by yourself though.

You basically remove all the wood, sand off any glues, and sealants leftover on the house and glass. Then measure, cut, and secure the new wood. This requires that you do proper joinery and routing though. What is needed depends on your window and frame. So only you could know if you’re up to the task.

An insert requires that only the rotted wood sections are removed. This will also require some joinery. It is unlikely that you will need to do any routing though.

Here is a video demonstrating the process of doing a wood insert into a frame.

Partial Wood Repairs

Partial frame repairs are the easiest of the three options. They require very little skill and effort. Partial frame repairs are also pretty cheap and can look great. By doing this repair though you run the risk of leaving rot in your wood and having to do it again.

As a note, wood filler takes 2-6 hours to fully cure and should not be touched until it is properly cured.

  • Remove the rotted portion of the wood
  • Apply wood hardener to the wood just underneath the rot
  • Apply two-part wood filler to the holes you’ve just created in the frame
  • Sand the filler flat
  • Paint
  • (From here the steps will only apply to any wood that is jutting and should be done before you paint)
  • Cut new boards to fit into the jut
  • Shape the wood
  • Seal any cracks
  • Paint

I have found a very good video on the process here. It goes over everything very well. It doesn’t need to be so messy though.

Full Epoxy Repairs

A full epoxy repair is likely the fastest and cheapest. Fastest meaning it requires the least amount of work time. It takes about two days to complete because there is a lot of waiting. The steps for this are basically the same as for a partial wood repair.

However, instead of putting in more wood you simply shape the epoxy to do your bidding. Here is a nice short video about it.

4. Securing The Fix

No matter how you choose to repair your frame rot, you have got to know some basics. Securing your fix is one of them.

Securing always requires a dry surface that has been properly prepared. How you prepare is determined by your method.

When doing a whole wood repair you will be securing wood to wood. This means you will be using glues and fasteners (nails and screws).

When doing a partial wood repair you will be securing wood to fillers. This means you will be using hardeners, glues, and fasteners.

Fillers have to have a dry and hard surface or they won’t work properly. To attach wood to the filler you need to use glue and fasteners.

When doing a full epoxy you need to make sure that the wood is paint-free, primed with a bonding agent.

Securing your wood is the most important part of repairing the window frame. Without proper securing the whole thing has the potential to be weak and insecure.

5. Shaping The Fix

Shaping is very important to your new wood not being noticed. Shaping can be achieved with sanding for everything but epoxy. Epoxy must be shaped with a form, then sanded after curing.

If there is a lot of shaping that needs to happen start with a lower grit count and move up to a higher count for finishing touches. A lot of shaping means more than just a few millimeters.

As a rule of thumb, I always say that anything more than one centimeter needs rough grit. Less than that and you can get away with finer grits.

6. Proper Sealing

Sealing is most important to keep your wood from rotting again. Proper sealing will increase the life of your wood greatly. Whereas improper sealing will allow your wood to deteriorate very quickly.

Seal any cracks with caulk. Fill any holes with spackle. Use a tool (or your finger) to remove any excess and give your wood that professional smooth look.

You can also use wood filler to fill in any crack. This is an excellent sealer but its sticky goopy nature can make it difficult to work with.

7. Painting

Of all the steps painting is likely the most important to giving your wood a longer life. If you paint properly it will form a protective barrier that will prove vital to increasing the longevity and prevent the rot of your new frame.

Choosing the proper paint and primer is very important. High-quality paints will be best for increasing the life of your wood. Aside from that, applying a few coats will go a long way towards keeping your wood alive.

8. Final Examination

This step isn’t just to admire your handy work. You need to look it over to see if you missed anything. Are there any open seams? Any thin spots of paint? Is everything sealed properly? If so you’ve done a good job. If not, get to it before rot sets in and allows you to hone those newfound window framing skills.

Ricky Kesler

With all of the projects I've done over the years, you'd think that I work on my house full-time. But I actually enjoy other things like spending time outdoors and time with my family.

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