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  1. #1
    Join Date
    Oct 2008
    Posts
    9

    Default Replacing rotten window sills

    I am replacing some rotten window sills. (These are the exterior sills, not the interior ones, AKA stools.) I have already removed one ( la the Tom Silva video) and am having the wood for the replacement sills milled from its profile. I plan to cut the side-horns (or whatever you call them) on the replacements as I remove the old sills. I will then prime them all over, especially the end grain, and will caulk appropriately.

    My question has to do with attaching them. Must I use nails? I don't have a nailer and really don't want to spend the bucks on one right now. Wouldn't screws work just as well? They would certainly make life easier for the next owner to replace these sills a hundred years from now.

    Any other helpful hints?

  2. #2
    Join Date
    Sep 2012
    Location
    Boston
    Posts
    1,004

    Default Re: Replacing rotten window sills

    put a thick bead of caulk between the new sill and where you're going to attach it. then predrill 3-4 holes in the new sill slightly smaller than the diameter of the screw threads. then use a countersink bit in the same hole which will allow the recessed screw head to sit within the sill. then you can fill the hole over the screw head and paint. make sure to use long enough screws, 3' - 4" - 5" that are made for exterior use, NOT drywall screws.

  3. #3
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,736

    Default Re: Replacing rotten window sills

    Use deck screws, rated EXTERIOR. Drywall screws rust and break over time.

  4. #4
    Join Date
    Oct 2008
    Posts
    9

    Default Re: Replacing rotten window sills

    Thanks for the good advice. Looks like I will be using pine for the sills. Any hints on primer or top coat? I'm thinking oil-based. That's what's on the rest of the window trim and it seems to have stood up pretty well.

  5. #5
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    6,736

    Default Re: Replacing rotten window sills

    Before you run and buy pine, take a look at POPLAR - it might be better for your task.

  6. #6
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    1,703

    Default Re: Replacing rotten window sills

    I've had much better luck with oil base on wood outside.
    I would add who cares about 100 years from now. Predriling for nails in the sill and using nails may be better because the smaller head is less to fill and less likely to crack and let water in.

  7. #7
    Join Date
    Jan 2008
    Posts
    2,203

    Default Re: Replacing rotten window sills

    Go with Fir or Poplar for the wood species. Pine usually has a wide hard-and-soft grain structure and the soft is just too soft; it will erode or rot more quickly. And I'd use finish nails (pre-drilled if needed) as they will provide less 'splitting' pressure but will hold well enough. They worked for the fist hundred years didn't they? Caulk and paint well, then check back in a year in case the wood shrinks a bit. I prefer oil based paints for durability and with many species of wood, they will penetrate and harden the surface of the wood whereas latex paints usually just sit on top waiting to come off someday. Once again, oil based paints worked for 100 years so why change now?

    If you give it some thought, old houses can teach you a lot which is still relevant in new construction today, though rarely seen More's the loss, but you've got yours and you still will have when their's is gone!

    Phil

  8. #8
    Join Date
    Oct 2008
    Posts
    9

    Default Re: Replacing rotten window sills

    Quote Originally Posted by dj1 View Post
    Before you run and buy pine, take a look at POPLAR - it might be better for your task.
    It's too late, already ordered the pine, specifically Eastern White of D or better grade. I'm not sure what all that means, but it looked pretty good. The old sills appear to be pine and lasted pretty well until the woodpeckers knocked the paint off.

    Just out of curiosity, why poplar? Where I'm from (Midwest) and where I live now (West), poplar has a bad reputation of being weak and rotting easily.

  9. #9
    Join Date
    Oct 2008
    Posts
    9

    Default Re: Replacing rotten window sills

    Quote Originally Posted by Mastercarpentry View Post
    Go with Fir or Poplar for the wood species. Pine usually has a wide hard-and-soft grain structure and the soft is just too soft; it will erode or rot more quickly. And I'd use finish nails (pre-drilled if needed) as they will provide less 'splitting' pressure but will hold well enough. They worked for the fist hundred years didn't they? Caulk and paint well, then check back in a year in case the wood shrinks a bit. I prefer oil based paints for durability and with many species of wood, they will penetrate and harden the surface of the wood whereas latex paints usually just sit on top waiting to come off someday. Once again, oil based paints worked for 100 years so why change now?

    If you give it some thought, old houses can teach you a lot which is still relevant in new construction today, though rarely seen More's the loss, but you've got yours and you still will have when their's is gone!

    Phil
    Thanks for the good info. Already bought the pine. Fir I can understand, but why Poplar?

    Yup, my old house has taught me a bunch. Never want to fix up another, though. I'm counting on "aging in place", especially given how much this place has aged me!

  10. #10
    Join Date
    Aug 2008
    Posts
    78

    Default Re: Replacing rotten window sills

    I've used short lengths of pressure-treated framing lumber for replacement sills (2X6, 2X8, 2X10, 2X12) over the years with excellent results; some diy sites recommend leaving the new PT wood exposed for a few weeks before painting, but I've never had any problems.

    Sometimes the lumber yard/home-improvement store has PT wood scrap pieces in the lumber section discard pile.

    Ditto on the rust-proof deck screws.
    Last edited by von_steuben; 07-18-2014 at 02:00 PM.

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