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Basement window interior sill

Posted: Wed Jul 10, 2019 10:30 pm
by KevP
Hey guys,
I previously posted about this but now have some ideas as Im getting ready to replace the windows.
My basement windows are set in mortar (only bottom) and they are in a bad shape (leaky and rotting). They are almost 70 years old. I ordered Andersen 100 series since the masonary opening is not standard.
Im not installing a wood buck since it takes 3 inches and make the windows too small. I have had few people tell me just foam it in place. I have a feeling a fastener is the better way to go.
Foam can deteriote over time but maybe im thinking too much.
Any tips on tapcons and size. I read lots of reviews on how some people had issues with them ( stripped holes or broken ones)
Second thing is that the mortar used to set the window is formed in a way that both inside and outside have slopes.
Should i keep the slope or try and make the sill flat? If needed to be flat, should i hack a way to make the jamb look flat or should i remove the sill partially and replace it with TP board or mortar. The slope from the highest to lowest is around 2 inches tall so a 2x and jamb would cover the gap. Any thoughts?
Removing the sill is tricky and if it cracks, then I need to redo the whole thing. I added images for reference.
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Re: Basement window interior sill

Posted: Thu Jul 11, 2019 7:24 am
by Shannon
You for sure wanna keep the outer slope. The inner slope can be covered with a flat drywall or wood piece if you finish the basement at some time.

Some manufactures have install straps that you can attach to the outside of window jambs (the area that will be in the wall) then slide the window into place ,shim it , foam it and finally fasten the straps to the wall. These straps then would get covered up by the interior jambs you add after.

I have never used them but I know some window manufactures have them.

Alternatively depending on the window jamb you could run Tap cons through the jambs into the concrete . Maybe get ones that will penetrate about 1" and around a 1/4" diameter.

I have removed older windows that were sprayfoam insulated and after the fasteners where removed I can not get the window out, I have to use a recipe saw and cut around the opening through the foam to release them. It holds very well. Beware though if the jambs are more then 16" long and the windows are not fixed units or you are not using mechanical fasteners you will want to place "spreaders" in the jambs to keep the window frame from being pushed out of shape with the foam.

Re: Basement window interior sill

Posted: Thu Jul 11, 2019 7:26 am
by Shannon
Here is some info from Andersons website.https://awwebcdnprdcd.azureedge.net/-/m ... 005519.pdf

Re: Basement window interior sill

Posted: Thu Jul 11, 2019 3:12 pm
by KevP
Thanks Shannon. Yeah I look at that manual before.
The jamba are 22 inches tall. I was planning on keeping the outer slope for sure.
I am in the process of framing the basment but held off on this section to not have the framing in the way of window installtion. After I posted I thought of maybe creating a wedge out of xps that fill the gap if I decide to go with a flat interior sill vs sloped. In case of sticking with the slope i think ill use pvc board since it wont rot in contact with the mortar.

Thanks for the spreader tip

Re: Basement window interior sill

Posted: Thu Jul 11, 2019 3:16 pm
by KevP
Any tips on tapcons to prevent issues? I heard 1/4 performs bettern than the 3/16

Re: Basement window interior sill

Posted: Thu Jul 11, 2019 9:52 pm
by Shannon
1/4" is really all you need for this. Drill the holes at least 3/4" deeper than needed.

Re: Basement window interior sill

Posted: Sat Jul 13, 2019 5:57 pm
by KevP
Hi Shannon,
As expected it is complicated for no good reason :D
So they embeded the bottom plate with a slope and now im left with a tiny peak and two sloped on each side. Im having a hard time setting the window since it wobbles. Really cany shim the bottom well. Making this thing plumb is a nightemare due to the wobble.
They also attached the window to the side with an old school method. They created a channle with mortar between the two blocks and placed a 3/4 by 3/4 piece of wood in there and nailed the window to it. The old window jamb are 1/2 inch wider so my screw holes fall in the channel. I guess i have to go into motar. Something like a 2 3/4 or 3 of length ( 1inch window jamb thickness + 1/4 gap + 3/4 depth of channel + whatever needed to get to the available screw size)
Any tips on how to deal with this?
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Re: Basement window interior sill

Posted: Sun Jul 14, 2019 9:15 am
by Shannon
You can use some mortar or grout and fix up that bottom area a little,abnd while that is drying cut some wood strips and glue them into the groove on the sides if you want or use 3' tap cons into the mortar. That mortar may not be great as it is just kinda a filler /adhesive thrown in there. Try drilling it to see if it just crumbles

Re: Basement window interior sill

Posted: Sun Jul 14, 2019 10:57 am
by KevP
I mamaged to hack it and kind of make it work. The mortar fills very dence. I have a hard time chiseling it. All left is shimming the sides and tapcon. Im really hoping the tapcon does not give me a hardache. If it sticks the foam will make it rigid.

Re: Basement window interior sill

Posted: Mon Jul 15, 2019 8:19 am
by KevP
Hey Shannon. I ended up just setting it with foam. The mortar was not as good as i thought. I shimmed pretty tight without distorting the frame. Even without the foamni was unable to move it. I dont think this window is going anywhere anytime soon. :mrgreen:

Re: Basement window interior sill

Posted: Mon Jul 15, 2019 8:25 am
by Shannon
Ya foam actually is pretty solid.
You should have no issues , just be sure you are sealed up outside

Re: Basement window interior sill

Posted: Mon Jul 15, 2019 10:01 am
by KevP
Yup. I ordered matching color caulk from Andersen. I will be doing that next. Thanks a lot for thr help

Re: Basement window interior sill

Posted: Mon Jul 15, 2019 4:34 pm
by Shannon
That’s why we are here! Glad it worked out