Help, what is a Firming liquid for turn of the century crumbling mortar!?

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New Member
Jun 14, 2023
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Colorado Springs CO
Hi I need help on this subject please,

I'm searching for the definitive answer as to whether or not there is like a spray on liquid which will firm up house stone foundation/wall mortar.
These are turn of the century 1900, which the mortar is very crumbly. It is constantly slowly falling out.
I know home improvement books say to scrape out some of the old mortar and repoint the grooves with new mortar after wetting the surface with sprayed water.

*BUT I have seen some old 1900 walls in restaurants where the mortar seems firmed up and no longer crumbly as if it was sprayed with some kind of firming agent.

Otherwise is repointing the only treatment for such walls?

Thank you for your time and knowledge!

I know of nothing except chipping it out and pointing.
There is a variety of mortar stain kits out there to match mortar types and age.
On a construction project once, I saw masons painting the crumbly mortar with clear polyurethane varnish. The idea, according to one of them, was that the urethane gets absorbed and acts like an adhesive to stop crumbling.
I have to think (guess) that this adds no structural strength, but was used to keep dusting down. (Inside walls of a restaurant)

When a kid, I worked for a brick mason. He always said "Don't cheat- Dig Out & Repoint!".

If the mortar isn't in good shape and you do re-point, you may wish to consider from what the wall is built & if it is above or below grade. Mortar comes in various compressive strengths & water resistance levels. You want one that will break before the brick, block or stone breaks. The grades are: K, M, N, O, S. Some research is in order & will prove valuable.

Type K is often used for historical restoration. It is low strength and will break before the old, clay bricks. I use it at my 125+ year old, very soft brick house. It lasts many years, but if snow piles up and water gets in and freezes, it'll crack. A very little crushed charcoal is my coloring agent.

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