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I need recommendation for type of mortar offering good grip to repair old deteriorated mortar between masonry squares with a hole in the middle used for the balcony wall. This is a 20th story balcony in a Houston high rise building built in the 70s. The gaps are about 3/4 inch. Owner is responsible to fix the inside of balcony. The outside seems OK.

In addition to the mortar, I was thinking to use a stainless wire to wrap around the masonry square to add additional strength wherever mortar is replaced. Thank you.

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    Welcome. Please don't YELL AT YOUR VOLUNTEER HELPERS by using all caps. Also, product recommendations are off-topic here, though your question is valid if it's asking for mortar type. Let's stick to that point.
    – isherwood
    Sep 18 '20 at 16:46
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    What is a "masonry square"? How would wrapping wire around it not be hideous? It would be great if you could add a photo to your post.
    – isherwood
    Sep 18 '20 at 16:48
  • "wrapping wire around" an individual block in the joints will add nothing. If you are repointing ALL the joints and you laid wire into the back of the whole joint (top to bottom & wall to wall, across all the blocks) that might help to tie them together a bit, though presumably they should be "fine without it" or they would have been designed that way (20th story high-rise balcony railings being "rather important not to have fail & fall."
    – Ecnerwal
    Sep 18 '20 at 17:06
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Sounds like a pretty standard repointing job, other than the location - rake, chisel (or "grout-saw") out all the loose/deteriorated mortar to some convenient depth, wet the joints, pack in new mortar (keep it damp so that it cures, rather than drying out) and tool the surface. You'll find more information in general on "repointing brick" but it's essentially the same other than your joints may be a bit wider than a typical brick joint mortar-line.

1970's era construction is probably normal modern Portland cement based mortar. i.e. what your masonry supplier will have as mortar mix, not some weird old lime-putty stuff you might need for historical preservation, where using the modern stuff will cause problems since the wall was built with the old-style stuff.

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  • But the op asked what type of mortar to use...not how to repoint...(i.e.: rake, chisel, etc. to repoint.)
    – Lee Sam
    Sep 18 '20 at 19:36
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We use mortar that is weaker than the material of the wall. You also need mortar rated for exterior (freeze - thaw) ability.

There are four basic types:

Type M: Used for below grade and frost heaving and in contact with earth.

Type N: This is medium strength and is the most common and used on exterior walls.

Type S: This is medium strength but used for free standing walls that bend and where you need lateral strength.

Type O: This is the weakest and primarily used indoors.

I’d use Type S for lateral strength and resistance. (Your balcony will bend and flex.) You can forget the wire.

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