Historic Brick Homes in St. Louis: Masonry Guide
If your St. Louis house was built before about 1930, its brick is softer than modern brick and its mortar must stay softer still. A portland-heavy mix on soft common brick spalls the face off the wall within a few winters. That single rule decides whether a repointing job protects your building or slowly destroys it.
Why pre-1930 St. Louis brick is a special case
St. Louis was built out of its own clay. Local brickyards fired enormous quantities of common brick through the second half of the 1800s and into the early 1900s, and that brick went into flats, rowhouses, bungalows and storefronts across the city. By modern standards it is soft, porous and variable. The best fired units were turned face out on the street elevation and the softer ones went into the side and rear walls, which is why the front of your house so often looks better than the sides.
Soft brick is not a defect. Walls built this way have stood for more than a century because the whole system was designed to move and to dry. The brick absorbs water in a storm and gives it back to the air afterwards. Lime mortar in the joints flexes with seasonal movement and lets moisture out. Nothing in the wall is rigid and nothing is sealed.
The rule that governs every repair
Mortar must be softer than the brick it sits between.
That is the entire principle. Brick and mortar both expand and contract with heat and moisture, and something in the wall has to absorb that movement. If the mortar is the softer material, it takes the stress and wears slowly. That is why masons call mortar the sacrificial element. A worn joint is a repair you can make again in thirty years for a few thousand dollars.
Reverse the relationship and the wall pays. A portland-heavy modern mix can run several times stronger than soft common brick. The joint refuses to yield, so the pressure lands on the brick face, and in a freeze the face pops off. Spalled brick cannot be repointed back. Each unit has to be cut out and replaced. A great deal of what looks like natural weathering on St. Louis buildings is actually damage from repointing done in the 1970s and 1980s with a mix nobody thought twice about.
What lime mortar does differently
Lime based mortars are softer, more permeable and more forgiving. Under ASTM C270 the softer mixes are classified as Type O and Type K, with far lower compressive strength than the Type S and Type M mortars used for modern structural work. On soft historic brick that low strength is the point. The joint gives, the brick survives, and water that gets into the wall can leave through the joint rather than through the brick face.
Lime mortar also has a habit that portland does not. Fine cracks in a lime joint can reseal over time as free lime moves with water and recrystallizes. It is slow and it is not magic, but a lime pointed wall ages differently from a cement pointed one.
Freeze and thaw is the mechanism behind most damage
St. Louis winters do the worst thing possible to masonry. Rather than freezing hard and staying frozen, temperatures cross the freezing line back and forth through the season. Every crossing works on the water already inside the brick. Water expands as it freezes, and if it is sitting behind the hard fired face of a soft brick, that expansion pushes the face away from the body.
This is why the sequence of repairs matters so much. Keep water out of the wall and the freeze cycles have nothing to work with. Seal a wet wall and you have locked the mechanism inside.
Spalling and efflorescence tell you different things
Spalling is the face of the brick breaking away, exposing the coarse interior. It means water got in and froze, or that hard mortar directed wall movement into the face. It is physical damage and the unit has to be replaced.
Efflorescence is the white powdery crust that appears on brick and stone. It is salt, carried out of the masonry by water and left behind when that water evaporates at the surface. The salt is harmless in itself and brushes off. What it tells you is that water is actively moving through your wall. Treat it as a reading rather than a stain, and go looking for the source.
Historic district review in St. Louis
The City of St. Louis has local historic districts covering neighborhoods including Soulard, Shaw, Lafayette Square, Compton Heights and others. In those districts the Cultural Resources Office reviews exterior alterations, and the district standards frequently govern mortar composition, joint width, profile and tooling. Separately, the City’s Building Division treats tuckpointing and structural masonry repair as permitted work, and your contractor should pull that permit rather than hand it to you.
Note that being listed on the National Register of Historic Places is not the same as being in a City local historic district. National Register listing is largely honorary for a private owner using private money. Local designation is what brings design review.
Outside the city limits the rules change again. University City, Webster Groves and Kirkwood are separate municipalities with their own building departments and their own preservation commissions. The permit and any review come from them.
What to ask any mason before you hire
Ask these before you sign anything. The answers separate the people who understand old brick from the people who own a grinder.
What mortar mix will you use on my wall, and why that one? A specific answer naming a type and a reason is what you want. A shrug or “the same as everybody uses” is not.
How did you decide my brick is soft or hard? Look for a real method: probing, water absorption, looking at the original mortar, or a lab analysis.
How deep will you cut the joints? Roughly twice the joint width is the standard answer. Anything under half an inch is too shallow.
Will you grind or chisel? Grinders widen joints and nick brick edges on soft masonry. Ask where they will and will not use one.
Can I see a cured color sample on my own wall before you start? Wet mortar always looks darker than cured mortar, so a match judged wet is not a match.
Will you match the joint profile and tooling? A concave, weathered, flush or beaded joint each throws a different shadow. The wall will look wrong if this is ignored, even with perfect color.
Who pulls the permit, and have you checked whether my address is in a historic district? The contractor should own both answers.
What will you do about the water? Pointing alone rarely fixes a wet wall. Expect the sills, the crown, the coping, the gutters and the grade to be part of the conversation.
And one more. Ask what they will do if they open the wall and find the problem is worse than the estimate assumed. A written scope with unit prices means you already know what the extra costs before anybody has to negotiate on a scaffold.
Common questions
How do I tell how old my brick is?
The city and the county both hold assessor records with a build year, and that is the fastest check. Beyond the date, soft older brick tends to look irregular, with a slightly rough face, rounded edges and visible variation between units. Harder later brick is uniform in size and color with sharp edges. If the original mortar crumbles under a fingernail it is likely lime based.
What is a mortar analysis and do I need one?
A lab takes a sample of your original mortar, dissolves the binder and reports what it was made of and what sand was used. It costs a few hundred dollars and it removes the guesswork on the mix and the color. It is worth it on a significant building, on anything from before about 1880, and on any wall where a previous hard repointing has already caused damage.
Is my house in a local historic district?
The City of St. Louis publishes its local historic district boundaries, and the Cultural Resources Office can confirm an address. Being on the National Register is a different thing from a City local historic district, and only the local designation brings design review of exterior work. University City, Webster Groves and Kirkwood run their own separate preservation processes.
Can a historic district tell me what mortar to use?
Yes, and that is usually a good thing. District standards commonly address mortar composition, joint width, joint profile and tooling, precisely because hard mortar and over-wide grinding have done so much damage to old brick. A contractor who treats the standards as an obstacle is telling you something about how they would treat your wall.
Does repointing hurt the value of an old house?
Good repointing protects it. Bad repointing is one of the fastest ways to damage a historic brick building permanently, because a ground-out, over-wide joint filled with hard grey mortar cannot be undone without cutting it all back out again. Spalled brick faces do not grow back. The cost difference between careful work and careless work is small next to that.
What should I do before winter if I cannot afford full repointing?
Deal with water at the top first. A cracked chimney crown, a missing parapet coping, a blocked gutter and a downspout discharging at the wall all feed more water into masonry than open joints on a wall face do. Spot pointing on the worst areas and correcting the roof drainage will carry a building through a season while you plan the bigger work.
Is sandblasting ever acceptable on old brick?
No. Abrasive blasting strips the hard fired outer skin off soft brick and leaves the porous body exposed, which then soaks up water and fails fast. It is the single most damaging thing commonly done to historic brick, and it cannot be reversed. Cleaning should start with the gentlest method that works, usually low pressure water and an appropriate detergent.