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How To Repair Rotted Window Frame [Inc. Interior And Exterior]

Untreated wooden window frames will rot over time, especially when they are exposed to the elements. When this happens to your window frames, there are ways to repair them. If you are looking for easy steps to repair a rotted window frame, this post is for you. We have done our research to help you out with this concern.

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Repairs to a rotted window frame depend on the extent of the rot around the window. However, you'll find that the fix isn't that complicated. Follow these steps to restore a rotted window frame:

  1. Inspect the area
  2. Remove any rotted sections
  3. Treat the frames
  4. Mix a two-part epoxy wood filler
  5. Apply the filler
  6. Let the filler dry
  7. Sand the frames
  8. Paint

This post will cover each step in detail. We will also discuss how to maintain window frames to avoid rotting. Continue reading for more information on these topics.

Decaying old building with weathered window frame and peeling paint. - How To Repair Rotted Window Frame [Inc. Interior And Exterior]

Window Frame Repair

Rot can happen on both indoor and outdoor wooden frames. However, it is commonly seen on exterior window frames, as these are more exposed to the elements.

Woman painting window frame at home,

Repairing the rotted area is easy, provided that you act on the damage as soon as you notice it. These steps are applicable to both indoor and outdoor window frames.

1. Inspect The Area

The key to a successful repair is knowing the extent of the damage.

Rotted areas in the window frame can be visible, but when you inspect the window further, you’ll see more hidden parts that need attention. You have to get to all these before the damage becomes irreversible.

2. Remove Any Rotted Sections

Use a utility knife, a scraper, a claw hammer or any object to remove any rotted sections. In some instances, scrapping is enough to remove the softened wood. However, the rot may have gone deeper, and you’ll need a drill bit to grind down to solid wood.

The key here is to get rid of all the decayed sections, because if there is some rot left, it will just continue to affect the other parts.

Before you move on to the next step, scrape off any paint on the window frames. Use a scraper or sandpaper to get rid of the old paint. Fillers and wood restorers won’t work if you leave paint behind.

3. Treat The Frames

Another important step is treating the remaining healthy part of the window. Adding a wood restorer will make the remaining parts sturdy.

Click here to see this wood hardener on Amazon.

4. Mix A Two-Part Epoxy Wood Filler

woodwork. Putty knife in man's hand. DIY worker applying filler to the wood. Removing holes from a wood surface. Preparation of wood before impregnation with varnish. Application of putty.

This type of wood filler is effective not only in patching small holes but also sections of window frames. Epoxy wood fillers are often used to restore wood pieces because they are cost-efficient. They easily fix the areas that remain after removing rotted wood.

An epoxy wood filler flexes with wood. So when the wood expands or contracts, the filler goes with it.

When mixing a two-part epoxy filler, do it on a non-porous surface so the mixture won’t stick to it. If you can’t estimate how much you need, you should mix small portions first.

Don’t mix the entire thing altogether because this filler dries fast. You won’t be able to manipulate it after a couple of minutes.

When you see the epoxy filler’s colors merge, you can apply it.

Click here to see this epoxy wood filler on Amazon.

5. Apply The Filler

Using a spatula, apply the mixed filler to the area where the rotted part was removed. The filler will fill the void and rebuild the part where the rot used to be.

Make sure that you push the filler through the void and don’t neglect the nooks and crannies of the window frames. Follow the shape of the window frame when applying the filler, so that when it dries, it’ll look like nothing happened.

Remove any excess when you’re done filling the void.

6. Let The Filler Dry

A wood filler’s curing time depends on the size of the area you’ve filled and how deep the filler was applied. Some fillers may take 12 to 48 hours to dry completely.

Remember to let the filler set completely before you move on to the next step. There are ways to hasten the filler’s drying time.

If you are working indoors, set up a fan for the air to circulate. This will aid in a shorter drying time. If you are working on exterior window frames, working in warmer weather will help in faster drying time.

In addition to these, a heat gun can also be used to heat up the filler for quicker drying.

7. Sand The Frames

Once the epoxy wood fillers dry and cure, you should be able to see that they’ve filled in the spaces where the rot was. You will need to sand the surface to trim off any excess filler and get a smooth finish.

8. Paint The Frames

When you are done sanding the filler, you’ll be left with a window frame that is obviously patched, as there is a difference between the color of the wood filler and the wood itself.

Luckily, you can paint epoxy wood filler. Some fillers are also stainable. 

Painting the window frames will make them look as good as new. You should choose a paint that’s water-resistant, so you won have to worry about the rot coming back, especially on exterior window frames.

Another Way To Repair Window Frames

When your window frames are badly rotted, wooden fillers may not work anymore. However, there is still a way to fix the window without replacing the entire frame.

Check The Area Around The Window

When you determine that a section is damaged and cannot be fixed by merely patching with wood fillers, you need to cut a replacement piece.

Pry Out The Section

Measure the part that will be removed and mark it to be cut. Use a cutting tool that can be operated in tight spaces, such as an oscillating multi-tool, to cut that part.

Use a crowbar or claw hammer to pry out the cut part. Be careful in doing this, as you don’t want harm any undamaged areas.

Make A Replacement Piece

Measure the part or section that you have removed so that you can cut a piece of new wood to replace it. The replacement piece should be identical in dimensions and texture to the one that you’ve removed.  

Seal Cracks or Gaps

Before installing the replacement piece, caulk any visible gaps as necessary.

Cut The Replacement Piece

Make sure that the dimensions are correct before cutting the replacement piece, so that it fits like a puzzle piece. The replacement should not be too obvious when you are done.

Install The Replacement Piece

You can secure the piece with nails or use small screws, depending on the depth of the wood.  If the nail or screw heads are visible, you hide them with wood filler.

Paint The Frame

Once you have installed the replacement piece, you can paint it. Paint will hide the replacement piece and protect the frame.

Click here to see this waterproof paint on Amazon.

How Can You Prevent Window Frames From Rotting?

Old wooden window frames with rotting wood and cracked peeling paint, house needs renovation and new frames closeup

One sure way to keep window frames from rotting is by painting them with waterproof paint. Apart from that, here are some tips to keep rot away from your windows.

Use Wood Sealers

Click here to see this wood sealer on Amazon.

If you don’t want to paint the window frames, you can use a waterproof sealer. Some wood sealers are clear colored. A wood sealer can help stop wood frames from absorbing moisture and prevent them from rotting.

You shouldn't let moisture seep into your wood frames.

Observe Proper Ventilation

Open your windows often for better air circulation.  After it rains, make sure that you also open the windows to let them dry.

Inspect The Windows Regularly

A man's hand checking the grid of a window

As mentioned in the previous section, the earlier you detect the rot, the better. Inspection will also let you see any changes in the frames, such as cracks or holes.

When you spot a small hole or crack, immediately fix it. These cracks and holes will let water seep through and eventually that part will start to rot.

Do Not Ignore Discolored Spots

If you see a spot that’s different in color, poke it. If it is soft to the touch, it is highly likely that there is rot on that spot. You should immediately treat it so that it won’t spread.

Final Thoughts

Repairing rotted indoor and outdoor window frames is an easy task, provided that you spot the rot immediately. You can fix the rot by patching epoxy wood fillers.

Once the fillers are dry and cured, they should be shaped like your old window frame. For large areas of damage, you may need to install a replacement piece.

Ultimately, you can prevent your window frames from rotting. Scrutinize your frames regularly to see if there are telltale signs of rot so that you can nip it in the bud. Remember: prevention is always better than the cure.

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