Doors and Windows - repacing basement windows in concrete

This is my first post to any kind of forum. I have read some old threads on replacing metal frame basement windows, but I still have a question on preparing the rough opening.

I have metal framed windows that are recessed into the concrete/mortar on the sides and bottom. I think I know how to remove them OK. My question is with the sloped mortar. Since the metal frames are so thin the slopes come to a narrow point in the center on the bottom. The vinyl replacements have a deeper frame. How do I seal up the bottom? Should I chisel out the slopes and mortar new ones?

Also, if I choose a replacement without the nailing flange, do I just screw the new frame into the concrete? What is the best way to seal the gaps?

Thanks for any help!!!

I use two methods, depending on the condition of the metal frames. If not badly rusted, I leave them in place as backers for the new vinyl windows(no nail fin). If no good as backers, tear them out. A couple of whacks with a 3# maul, and the sloped cement will crack and be easy to remove w/hammer and chisel. The sides are usually set in a slot, so cut one bottom with a sawzall and they will bend out for removal. You can size the new windows to exactly fit the opening, or rim it with PT wood, and size to fit that. Either way needs some caulk and tapcons. Fill any air gaps with DAP Foam or NON-expanding foam.

Just Bill,

Thanks for the quick reply. I wasn't sure how easily the mortar would come out. It's hard to tell if it was poured with the wall or after the fact.

I aslo read in another thread that I need to have some slope to shed rain water. Do I need this in mortar, or will the vinyl window frame do this for me?

The mortar was done when the windows were set. Sometimes one pop with a hammer and it all comes out, sometimes it takes a while.
Slope is not an issue with vinyl windows. They have drain holes if not sloped.

Thanks again! Your making this sound pretty simple.

In most cases, I rip the old frame out, and leave the sloped cement cap, provided it is in good shape, not broken up. The new window usually covers the area the old window was in, covering up any rough looking concrete.

I don't like messing around with concrete, or making a special trip back to caulk the bottom once the cement cures... so I like to leave the original sloped sill whenever possible. But every window is different- you'll figure out what is best I'm sure.