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Replacing Leaky Rotted Basement Windows – Part 3 of 3



  • I am going to temporarily place my new replacement window to see how it fit
  • I am not too concerned about small gaps on the bottom as they will be sealed by an expanding window foam
  • You want a good solid bonding between caulking/foam against all surfaces so take your time and clear off any small debris /dust from the surface.
Fig 9.1.a
Fig 9.1.b
  • I used a can of compressed air (didn’t want to use my compressor as it was way too powerful and would generate too much dust) to blow off any concrete/mortar dust before applying a beat of caulking around the header, side and bottom of the opening
Fig 9.1.c – Can of compressed air
  • Next, I used a clear caulk because it gave me most flexibility in terms of it blending it with the surrounding color. Although the caulk is white when first squeezed out, when it dried it became clear.
  • Also, I planned on attaching the window frame to the bottom of the sill plate so I DID NOT caulk the bottom of the window. However, I laid down 2 separate caulking tracks on the top part of the window as well as caulk line on the bottom of the sill to ensure a solid seal against draft.
Fig 9.2
Fig 9.3
  • Since I was skipping the window frame, I screwed in three, 2″ Deckmate screws, attaching top of the window to the house’s rim joist before sealing out the gaps with a can of low expansion window foam
Fig 9.4


  • There are numerous types of foam sealants out on the market. You need to make sure to purchase one that is specifically made for windows and doors because foam sealants can be powerful enough to warp or bend window or door frames
Fig 10.1
Fig 10.2
Fig 10.3


  • For the sake of image clarity, I had to use pictures from 2 basement windows
  • After couple of days, liquid foam has turned hard so it was easy to cut off the excess. Any sharp utility knife will do.
  • If you don’t already own one, get a Stanley Titan Utility Knife with a fixed blade This knife has a gentle curve that save your knuckles from being shredded by a hard concrete surface.
  • Once the foam has been cut, take a 6 inch drywall taping knife and scrape off the excess. There are so many uses for this taping knife so dedicate one for use around the house. Any kind will do like Marshalltown Joint Knife Made with Plastic Handle and Carbon Steel Blade. Avoid buying plastic ones as the blades will not survive being scraped on a hard surface
Fig 11.1 – cutting off excess foam
Fig 11.2 – metal blade to scrape off excess foam

Fig 11.3 – after removing excess foam
Fig 11.4 – exterior damage

To repair the damage, I needed a bag of mortar mix. Because this was my last window, I decided to purchase a small, ready mix bag from a local big box store. I don’t recommend buying this online due to shipping cost though Sika Corp. 05MG060 Sika Mix & Go

Fig 11.5 -new mortar
Fig 11.6 – mixing mortar
  • When mixing mortar, ALWAYS add less water than the stated amount. You can always add more water later.
  • if you have too much water, the only way to fix it is to have more dry mortar to mix in
  • As far as the consistency is concerned, think about a peanut butter jar that has been sitting out. Very easy to spread, but not drippy.
  • If you have a large chunk to repair, you will need to do it over the course of several days by adding a layer each time.
  • If you were to place a large amount of wet mortar in one place, it will most likely droop as well as form a crack.
  • The pictures I have is from my coating and you can see the depression on the left side of the window. I will be revisiting the window when the weather gets little bit warmer to add a final coat
Fig 12.1 – after initial mortar resurfacing
Fig 12.2 – side view


I am going to let the mortar dry out for about a week or so before fixing the corner.

After that, I will prime and paint the area to match the rest of the foundation.

Well, that’s it. If you found this article to be helpful, please click on one of the social icons to share it with your family and friends!


Wednesday 15th of February 2017

@Craig -- Thanks for the info about the mortar. I have steel frame windows embedded in concrete so patching up with mortar seems like a good way to make it look nice. I'm not quite there yet. My plywood window has some nice character to it :)

I have to second the recommendation on using power tools. I rented a hammer-drill and it was awesome for chipping away the concrete that was used as a bed underneath the old, very difficult to remove frame. I had to use a large pry-bar. Generally I did a little more damage than I would have liked, but I'm not sure how I would have gotten those beasts out otherwise. Way it goes I guess.

I felt like the hammer-drill really didn't make much more of a mess than a manual masonry chisel would have and it save me a LOT of time and grief - I got all the cement chipped out and a hole drilled for a bathroom fan before my 4 hour rental period was up! It was messy though I'm not sure how you get around that.

FWIW chipping out the concrete with the hammer drill makes less mess than the grinder, but the grinder gives a much better edge. Trade-offs I guess.

I was only somewhat successful at sealing off the dust :)

Craig W.

Thursday 4th of February 2016

Just for future readers that come across this...this is NOT a good way of doing this window install. All the spray foam and nothing else (except for the top) is no good. It is equally as easy, and better, to simply fill the gaps around the new window with mortar. You can lock the new window in place with mortar easily and still not use any wood. Install and level the window as shown here with screws through the top and some caulking. Then pack mortar all around the window frame. That's it. If you want a better "bite" for the connection of the window to the mortar around it, you can install screws into the outside of the new window all around its outside edge. Just don't screw too far in that it comes through the inside of the window frame. What you are left with are screw heads sticking out all around the outside edge of the window frame. How far they stick out is up to you. Generally 1/2" to 3/4" is fine. Depends how much room you have between the new window frame and the window opening. Then squish in mortar all around the window frame and all around the screws. Fill it up all the way around. Then finish the mortar as you want. Slope the sill if you want. With the mortar, repair any damage you made. Done. Very easy. No wood to rot out. And no ridiculously ugly and messy spray foam to seal anything up with.

Also, an angle grinder with stone cutting wheel or grinding wheel would have made your demo wayyyyyyyy easier and actually would be way cleaner and less likely of causing damage than chisels and hammers. If you use the right power tools it is way faster and more controlled.


Friday 5th of February 2016


Thanks for your comment. I do have some follow up questions:

1. When you pack the surrounding gap with mortar, how do you make sure it does not ooze out? Wouldn't you have to set up some sort of a form to prevent that from happening?

2. I did consider the power tool but it would have generated way too much dust Do you have any special power tools that you know if that can control dust?


Saturday 17th of October 2015

Unless I missed it, you didn't use anything but the expanding foam to attach the window to the house. Is that all that's needed? I'm asking because I'm about to replace two basement windows also. Thanks.


Saturday 17th of October 2015


Yes, in my case, I decided to use foam because of three reasons:

1. One basement window is under the newly installed deck and thus it is not accessible; 2. The other window faces 4 neighboring houses; 3. I wanted maximum light into the basement.

However, there are drawbacks: 1. Foam-only is obviously not as secure as attaching to a wood frame; 2. It takes time to chisel and even out the concrete opening; 3. Depending on how the condition of your brick exterior, you may need to patch it up (like I explained in the article).

If your window wood frame is in good condition (i.e. not rotted), I would keep it and just replace the window.

Hope this helps?

Kevin would be more secure, but I felt that it

Mary Ann Bunyan

Thursday 13th of August 2015

My house is masonry with wood trim on the outside. I would like to install the window from the inside and leave the wood trim in tack. Please advise.


Thursday 13th of August 2015

@Mary Ann-

If it is a basement window, all you have to do is take the interior measurement from left side jamb to right side jamb (plus top and bottom sills).

Although the glass area will be reduced somewhat, it's pretty much a drop in (like installing a replacement window) without disturbing the wood frame.

Please read Sections 1 and 2 to read about taking measurements.


Friday 10th of April 2015

Many thanks for taking the time to post both text words and supporting pictures. And, for posting your many great supporting tips as well. You do great work! And, your posted info will save me hundreds of dollars in the future - when I replace the old / leaky 4 x basement windows in my cottage. Thank you!


Thursday 7th of May 2015

thanks jack! nothing beats that awesome feeling when you get your diy project done the right way!