Author Topic: Destroyed my kids window sill, now I need to fix it!  (Read 924 times)


  • Bristles
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Destroyed my kids window sill, now I need to fix it!
« on: July 12, 2018, 02:54:37 PM »
Hey guys,

My daughter had some water damage on her window sill, and in the process of investigating the issue I may have inadvertently dug a hole in it and made a big mess (images attached).  Now I need to fix it.  Some of the wood is not in the best shape but my goal is to patch it and just seal it up so no more water/condensation can get into it.  Not being the handiest guy in the world I thought I'd come to my mustachian friends for advice.  I had two ideas for fixing it:

1) Squirt expandable foam in there. Shave it off so it's flat about 1/8" below the surface of the wood. Whack some drywall tape on there and then use drywall compound on top and re-paint.  My concern about this approach is that it won't be very strong and if someone put weight on it then the compound would crack due to the foam underneath not being super-solid.

2) Cut a big rectangular chunk out of the sill, then use a method like the one shown here: to attach some wood inside/under the gap to support a new piece of wood to stick on top. Then patch the edges/top with drywall compound till it's all level and smooth and paint over it.

Any thoughts or other suggestions would be appreciated. The rest of the sill is fine, it's just that patch in the middle which isn't in great shape.



  • Stubble
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Re: Destroyed my kids window sill, now I need to fix it!
« Reply #1 on: July 13, 2018, 08:44:23 PM »
I have seen old timers use Bondo for partially rotten wood that looks like your picture. Dig out all the soft stuff until you have good/firm wood left, then mix up a sufficient quantity of Bondo, spackle it in, smooth it a bit, wait until it dries, then sand flat and paint. Smells bad while drying.

Raymond Reddington

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Re: Destroyed my kids window sill, now I need to fix it!
« Reply #2 on: July 13, 2018, 09:11:57 PM »
Do NOT do #1, as you clearly have a moisture issue behind the window. If you reach in, with your finger you will likely continue to find moisture saturated wood beyond what came out already / what is visible from the surface. The expandable foam does not "breathe" and therefore traps moisture. Any moisture that penetrates / is already in there with nowhere to go will persist and continue to rot out the wood in there. You have to start by finding the source of the moisture. Start by checking any caulk seal between the window and the window frame from the exterior of your home, gaps in the caulk will allow moisture to penetrate between the window and the frame and cause this. Also check to make sure (if it's a top floor window) that you don't have any roof leaks, or leaks at the top of the window frame that are running down behind the wall and pooling in that area, causing the damage.

Once you address the issue, you can either putty or replace boards, depending on what you want the look to be. Either will look good with quality workmanship.
« Last Edit: July 13, 2018, 09:19:29 PM by Raymond Reddington »


  • Stubble
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Re: Destroyed my kids window sill, now I need to fix it!
« Reply #3 on: July 18, 2018, 05:02:52 AM »
I wouldn't do either.  #1.  Remove the window casing from around the window (use a small pry bar).  #2.  check between the window and drywall for moisture.  If you have moisture below the window, chances are, it has already run down the wall to the bottom of the framing.  If this is the case, the window needs to come out, the framing should come out as well around the window.  It should be re-framed, a sill pan should be installed and a new window installed and properly flashed from the outside.


  • Stubble
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Re: Destroyed my kids window sill, now I need to fix it!
« Reply #4 on: July 18, 2018, 10:23:20 AM »
Make sure to scrape out any rotted/soft wood. General rule of thumb: if it can be scraped off with a flathead screwdriver it needs to be removed.

I'd then put wood hardener on the rest of the wood

Once that application is done, then fill in material (differs depending on how large the void is, structural/non-structural). Finish off with sandable material though so you can paint to match & not tell a repair even took place.

Like others said you have to make sure the moisture entry is fixed before patching this though


  • Magnum Stache
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Re: Destroyed my kids window sill, now I need to fix it!
« Reply #5 on: July 25, 2018, 03:06:57 PM »
Definitely find the source of the leak first. It might take spraying the house from different angles with a hose. Water has away of getting in the strangest ways.  I ran into a similar situation with a home and it looked really bad. I opened up the drywall all around the window and fixed the leak. Then replaced the insulation. Was able to cut the sill out and replace and paint. Thought for sure I was going to be replacing about a 3k window but it turned out just fine.  As others have stated though it has to be dry before you seal that back up. One of those things get the prep done right!! You don't want mold in your house and on top of it your daughters room!!