Can You Caulk Mortar Joints Instead of Tuckpointing?

Can you use brick mortar caulk instead of tuckpointing? Not as a real repair. Caulk fills a visible gap, but it doesn't rebuild the joint, and what is wrong with the mortar is usually behind the gap, not in it.

A quick note on sources. The masonry guidance we cite covers mortar and repointing. It doesn't test caulk in brick joints, so we won't claim it does. What follows is the mortar principle from that guidance, applied honestly to what caulk is and isn't.

Why caulk is not mortar

Mortar and caulk do different jobs.

• Mortar is part of the wall. The NPS says new mortar should be softer than the brick and more vapor permeable, and that the joint is the sacrificial element where stress should be relieved (National Park Service).
• Caulk is a flexible sealant applied over a surface. It is not one of the ASTM mortar types, and it doesn't carry load or join units the way mortar does.

Repointing also isn't just filling a gap. The old mortar is removed to a depth of 2 to 2.5 times the joint width, about 1/2 to 1 inch for most brick, so the new mortar can bond properly (National Park Service). A bead of caulk pressed into a crumbling joint skips all of that. It sits on loose, failing material.

What caulk can hide

When mortar fails, moisture and dissolved salts have to go somewhere. The NPS describes how, when mortar is less permeable than soft brick, moisture moves out through the brick instead, and salt crystallizing inside can spall or delaminate the face (National Park Service). We don't have a source that says caulk does that. The point is narrower: sealing the surface of a failing joint doesn't fix why it failed, and it can cover the signs you'd otherwise see.

There is a code side too. Chicago's maintenance code lists masonry joints that are not weather resistant or water tight as an unsafe condition (City of Chicago code). The text doesn't name caulk, so whether a sealant satisfies an inspector is a question for the Department of Buildings, not for us. See what the code says about crumbling mortar joints.

When caulk is the right tool

Caulk has a place on a brick building, just not in the mortar between bricks. Gaps where the brick meets a window frame, door frame or other material are different joints from the mortar joints, and a flexible sealant is typically what those call for. If you're not sure which kind of joint you are looking at, ask a pro before you fill anything.

What to do instead

1. Check whether the mortar is really failing. Our article on signs your brick needs tuckpointing shows how.
2. If it is, repoint: remove the bad mortar and fill with the right mortar type. Wrong mortar causes its own damage, so read the mistakes that cost owners twice.
3. If you're thinking of sealing the brick afterward, see whether to seal brick after tuckpointing.

Not sure what you have? Our tuckpointing crew will look at the wall and tell you whether it needs repointing or something simpler. The Chicago tuckpointing guide covers the full 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.