Brick Mortar Turned to Sand: What Failed and What to Do

Brick mortar turned to sand is a joint that has stopped doing its job. You can scrape it with a key and it comes away as loose grains, or you find a little pile of it on the sill below the wall. It looks small. It is the wall telling you water is getting in.

What failed when mortar turns to sand?

Mortar is sand, a binder and water, cured into a solid. When it sands, the binder is no longer holding the sand. The grains are loose, so the joint has no strength and no seal. It also cannot do the job the National Park Service gives it: a joint is meant to be the sacrificial part of the wall, taking the wear so the brick does not (NPS Preservation Brief 2).

A joint in that state is on the City's list. Chicago's exterior maintenance code names masonry joints that are not weather resistant or water tight as an unsafe condition (City of Chicago). Sandy mortar is a plain example of one.

Why does mortar turn to sand?

There is rarely one cause, and we cannot diagnose a wall from a description. These are the usual suspects.

Age and water. Old mortar that has taken decades of rain, wetting and drying wears away from the surface. In older Chicago walls this is the first thing we suspect. Softer, lime-rich mortar was normal in historic masonry, and the NPS notes that more lime makes mortar softer and more permeable (NPS). Soft mortar wearing faster than the brick is how the system is supposed to work. The problem starts when no one replaces it.

Water that never gets a chance to leave. A joint takes more punishment where water pools or runs down the wall: below a failed gutter, a bad roof edge or a leaking sill. The mortar is not defective there. It is overworked. Fix the water and the joint repair holds.

A mix or curing problem in a recent repair. If the sanding mortar is only a few years old, look harder at the work. The NPS says high-lime mortar that dries too fast can chalk and lose adhesion and durability, and recommends misting the joints and covering the wall in the first days (NPS). Mortar mixed with the wrong sand or the wrong proportions can also fail early. Whether that is what happened to your wall takes a mason standing in front of it.

The brick has a problem too. Where the brick faces beside the sandy joint are flaking, the joint may not be the only failure. Freeze-thaw of saturated brick and salt crystallizing inside the brick can both make the face spall (NPS). That changes the scope.

What are the warning signs?

• Mortar that comes away as grains when you scrape it with a key or a screwdriver.
• Small piles of sand or grit at the base of the wall, on sills or on a porch floor.
• Joints that are recessed, with a rough, pitted face instead of a smooth surface.
• Gaps wide enough that you can see the edge of the brick behind the joint line.
• Water stains, damp interior walls or peeling paint on the inside, below the sandy joints.
• White powder on the wall. That is usually efflorescence, a salt deposit left when water moves through, and it points to water in the wall (BIA).

For a longer check you can do from the sidewalk, see how to tell if your Chicago brick needs tuckpointing.

How is it fixed?

The loose mortar comes out and new mortar goes in. The details decide whether it holds:

1. Cut out to depth. Old mortar is removed to a depth of 2 to 2.5 times the joint width, which for most brick joints is about 1/2 to 1 inch. Hand chisels are the least damaging method, and power grinders belong only in skilled hands on horizontal joints (NPS). Brushing off the sand and filling over it will not bond.
2. Match the mortar to the brick. The new mortar should be softer and more vapor-permeable than the brick and no harder than the original mortar. Assuming that harder is better is a common error (NPS). When mortar is less permeable than soft brick, moisture and salts leave through the brick and can make its face spall (NPS). We cover that failure in the mortar mistake that ruins Chicago brick.
3. Match the look and test it. The color and texture come mostly from the sand, plus tooling and joint profile. A test panel, about 3 feet by 3 feet for brick, sets the standard before the wall is done (NPS).
4. Cure it properly. Lime-rich mortar needs protection from drying too fast (NPS).

The Brick Industry Association says the terms tuckpointing and repointing mean the same repair (BIA), so a quote that says either one is describing this job. In Chicago it is permitted masonry work. The City's Express Permit program lists tuckpointing (City of Chicago), and masonry work on clay brick requires a licensed mason contractor (City of Chicago). Confirm the current permit rules with the Department of Buildings. What drives the price is covered in what moves tuckpointing cost.

What should you do this week?

Scrape a few joints on each wall and note where it sands. Take photos with a ruler or coin for scale. Look for the water source above the worst spots. Then get a mason to look at it, ideally one who will tell you which walls need work and which do not. Our tuckpointing crew does these assessments, and the Chicago tuckpointing guide lays out the whole process.

Common questions

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.