Lime Mortar vs. Portland: Why the Wrong Mortar Is Destroying Evansville's Oldest Brick

September 4, 2026

If you own a brick house in Evansville built before about 1930, the single most important thing to know about it is this: it was laid in soft lime mortar, and every time someone has repointed it since the 1950s with hard bagged Portland mortar, they have moved the freeze-thaw damage out of the joints and into the brick. The joint holds. The brick face pops. Walk any block of the Riverside Historic District, Washington Avenue, Bayard Park, Goosetown, or Lamasco and you can see it from the sidewalk: crisp grey joints beside brick with its face blown off. This post explains why that happens, what the National Park Service and the Indiana DNR say about it, and what a correct repoint looks like.

A short history of mortar, by date

The National Park Service’s Preservation Brief 2, Repointing Mortar Joints in Historic Masonry Buildings, lays out the timeline plainly. Traditional mortar was lime putty and sand, generally about one part lime to three parts sand by volume, sometimes with crushed shell, brick dust, or animal hair, and that basic recipe was unchanged for centuries. Portland cement was patented in Britain in 1824, first manufactured in the United States in 1872, and, in the brief’s words, “not in common use throughout the country until the early 20th century.” Up to the turn of the century Portland was considered an additive, a minor ingredient to speed the set. By the 1930s most masons used equal parts Portland and lime putty. So mortar in a building constructed between 1873 and 1930, the brief says, can range from pure lime and sand to a wide variety of lime, Portland, and sand blends.

Map that onto Evansville. The Riverside district was platted as the Upper Enlargement in 1819 and its 425 structures run from the Zurstadt House of about 1853 through the Reitz Home of 1871 to the Bosse House of 1916. Washington Avenue’s Italianate and Queen Anne houses date to about 1880. Culver started around 1890, Bayard Park after the 1893 deed restrictions that made it the city’s first planned development, and the Independence district in Lamasco after 1880. Nearly all of it was laid in lime, or in lime with a little Portland. Only Lincolnshire, platted after 1923, and the 1920s to 1950s East Side were built when a Portland-lime blend was standard.

Why soft mortar protects soft brick

Preservation Brief 2 states the rule twice, once for any masonry and once for historic masonry: mortar for repointing “should be softer (measured in compressive strength) than the masonry units, and no harder than the historic mortar.” The Indiana DNR’s guidance on historic brick says the same thing in one sentence: the new mortar “must have greater vapor permeability and be softer than the masonry units and must be as vapor permeable and as soft or softer than the historic mortar,” and if it is too hard “it can result in damage to the historic masonry, such as spalling, where the outer face of the brick pops off.”

The numbers make it concrete. The five standard mortar types, per the brief, have roughly these compressive strengths: Type M 2,500 psi, Type S 1,800, Type N 750, Type O 350, and Type K 75. Evansville’s 19th-century brick was fired in local clamps and kilns at uneven temperatures, and much of it is soft, with a harder fired skin over a sandy core. Put that brick in a Type S joint and the joint is many times stronger than the unit it surrounds.

Now add the weather. NOAA’s 1991-2020 normals for Evansville Regional Airport count 92.6 nights a year with a low at or below 32 degrees but only 15.5 days with a high at or below 32. On the difference, roughly 77 days a winter, the wall freezes overnight and thaws by afternoon. Water in the wall expands each time it freezes, and the stress has to relieve itself somewhere. In a lime-mortar wall it relieves itself in the joint: the mortar crumbles a little, and in forty years you repoint it for the price of mortar. In a Portland-mortar wall the joint does not give, so the brick does, and the fired face comes off in a dish-shaped flake. Once the face is gone, the sandy core absorbs water faster and the process accelerates.

There is a second mechanism. Lime mortar is vapor-permeable; water that gets into the wall dries out through the joints. Portland mortar is dense. Water that gets into an old wall through a cracked sill, a failed crown, or a hairline at a lintel cannot leave through the joints, so it leaves through the brick, carrying dissolved salts that crystallize under the face and push it off. That is the efflorescence you see, and the spalling that follows it.

What the damage looks like in Evansville

• Chimneys in Riverside and Bayard Park repointed in the 1970s and 1980s with grey bagged mortar: intact joints, spalled brick, often a cracked mortar-wash crown feeding the whole thing. The chimney page covers when that is a repoint and when it is a rebuild.
• North elevations in Goosetown and Culver: rows of spalled faces along the bed joints where a Portland repoint met a wet wall that never dries.
• Below limestone sills across all the districts: the sill lost its slope, the water ran into the joints below, the Portland held, and the brick under the sill is gone. See the stone page.
• Sandblasted or painted walls in Lamasco and along West Franklin Street: the DNR guidance names sandblasting as the most common damaging cleaning treatment, because it removes the fired skin, and paint as a moisture trap that spalls brick. A sandblasted wall repointed in Portland is the worst case, and there are plenty of them on the West Side.

Testing what you have

A mason can usually tell from the wall. Lime mortar is soft enough to scratch with a key, off-white to tan, with visible sand and sometimes shell or hair. Portland is grey, hard, and rings under a trowel. A sample can be dissolved in a weak acid to separate sand from binder and match the sand’s color and gradation, which is how the new mortar gets matched. On a Riverside house the mortar match is not optional, because the Historic Preservation Commission’s District Guidelines list masonry as a reviewed project and a mismatched joint is a conspicuous change.

What a correct repoint looks like

1. Remove the hard mortar. To a minimum depth of 2 to 2.5 times the joint width, per Preservation Brief 2, which is 1/2 to 1 inch on most brick joints. On soft brick this is hand chisels and mash hammers, which the brief calls the method that “poses the least threat for damage to historic masonry units,” or a skilled hand with a small grinder on bed joints only. The DNR guidance shows what grinder damage looks like at the head joints when it goes wrong.
2. Replace the spalled brick. From salvage, matched for size, color, and texture, at $20 to $40 per brick. The brick repair page covers the match.
3. Mix a compatible mortar. For most pre-1930 Evansville brick that is a lime-rich Type O or Type K, or a straight lime-sand mix, with the sand matched to the original. For 1920s to 1950s brick, Type N. Type S only on modern brick and block.
4. Pack in lifts. Joints dampened, mortar packed in roughly 1/4-inch layers, each allowed to reach thumbprint hardness before the next, so the shrinkage happens in thin layers instead of one deep crack.
5. Tool to match. Grapevine, beaded, concave, or flush, whatever is on the wall.
6. Cure. Lime mortar cures slowly by carbonation; it is misted in heat and protected from freezing for days, not hours, and never placed with the wall below 40 degrees and falling. NWS Paducah puts Evansville’s average last freeze at April 6 and first at October 29, so this is April-to-November work.

Done that way, the brief says, a repointing job should last at least 30 years and preferably 50 to 100. Done with a skim of Portland over the old joints, it lasts two Evansville winters and takes brick with it. The tuckpointing page has the full process and the pricing page has the numbers: lime work runs $12 to $20 per square foot against $8 to $14 for modern brick, and it is worth every dollar of the difference on a house that has stood since the 1870s.

The honest bottom line

If a bidder on a pre-1930 Evansville house does not name the mortar type on the quote, does not mention removing the old hard mortar, and does not talk about matching the sand and the joint profile, they are going to reach for a grey bag. That repair will look fine in the photo and it will cost you brick. Ask three questions: what mortar, how deep, and how will you tool it. The right mason has answers for all three before the ladder comes off the truck.