Grind or chisel old mortar out to a depth of 2 to 2.5 times the width of the joint, according to the National Park Service. For most brick joints that works out to about 1/2 to 1 inch. Shallower than that and the new mortar has too little to grip, so it pops out. Any loose mortar deeper than that should come out too, and the work should be done carefully so the brick is not damaged.
Ask three crews how deep to grind out mortar joints and you may hear three answers. The preservation guidance has one: a depth tied to the width of the joint. Here is the rule, how to apply it with a tape measure, and what a short job looks like on your wall.
What is the right depth?
The National Park Service says to remove old mortar to a depth of 2 to 2.5 times the joint width, so the new mortar bonds well and does not pop out. For most brick joints that means about 1/2 to 1 inch. It also says loose mortar deeper than that should be removed too (NPS Preservation Brief 2).
The same brief notes that hand chisels are the least damaging way to remove mortar. Power grinders belong in the hands of skilled masons, working only on horizontal joints and with care (NPS Preservation Brief 2). The depth rule is the target. How the crew gets there is where the brick either survives or does not.
How do you apply it to your joints?
Measure the width of a joint, then multiply. A joint 3/8 of an inch wide should be cleared to roughly 3/4 to 15/16 of an inch. A narrower joint needs less depth, and a wider one needs more. A crew that grinds every joint to the same depth without looking at the width is not following the rule.
You can check this yourself during the job. Ask the crew to show you a section after the old mortar is out and before the new goes in. The slot should be clean and free of loose crumbs. If you can see the old mortar still sitting a quarter inch from the face of the brick, the job is not deep enough.
On Chicago brick two-flats and three-flats we often see joints that were scraped out just deep enough to fill, then packed with fresh mortar that sits on the surface. It looks tidy for a season or two. Then it starts falling out in sheets, because it never had depth to grip.
What does the dust have to do with depth?
Everything that cuts depth also makes dust. Federal rules for grinders used on mortar require a commercially available shroud and a dust collection system, and respirators for the crew (OSHA). A crew that is serious about depth is usually serious about this too. The dust side has its own article: tuckpointing dust, and what to expect.
Depth is also only half of a lasting job. The new mortar should be softer and more vapor-permeable than the brick (NPS Preservation Brief 2). The full list of what goes wrong is in tuckpointing mistakes that cost owners twice. If you are wondering whether you can do this yourself, read DIY tuckpointing in Chicago first, and see our tuckpointing guide and tuckpointing service for the rest.
Common questions
To 2 to 2.5 times the joint width, per the National Park Service. For most brick joints that is about 1/2 to 1 inch. Measure the joint first, then multiply. Loose mortar deeper than that should be removed as well.
Yes, in the sense that careless grinding can damage the brick, which is why the National Park Service says power grinders need skilled hands and care. The target is the depth rule above, not as deep as the blade will go.
The National Park Service calls hand chisels the least damaging method and limits power grinders to skilled masons working on horizontal joints. Any grinder on a job should have a shroud and dust collection under the federal silica rule.
Sources
- National Park Service: Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings (PDF)
- OSHA: 29 CFR 1926.1153: Respirable Crystalline Silica in Construction
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.