Limestone Cornices, Belt Courses, and Water Tables: Profiles That Shed Water

Look at almost any classical stone building and you will see horizontal lines running across the face: a heavy cornice at the top, bands at the floor lines, and a beveled course near the ground. They organize the facade, but their first job is practical. Each one throws water away from the wall below it.

This post covers what cornices, belt courses, and water tables are, how they shed water, how projecting stone is supported, and what goes into fabricating long runs of profiled limestone.

Three Horizontal Courses

The Parts of a Cornice

A classical cornice is built up from a sequence of moldings, each with a purpose.

• Bed mold. The lower moldings that step out from the wall and visually support the projection above. Dentils, the small repeated blocks seen on many cornices, sit in this zone.
• Corona. The flat, vertical face of the main projection. Its underside, the soffit, carries the drip. On more elaborate cornices, the soffit is supported by modillions or brackets.
• Crown (cymatium). The top molding, often an S-shaped curve, which finishes the profile and leads into the sloped top surface.
• Wash. The sloped top of the stone. It is not visible from the street, but it is the most important surface on the cornice for keeping water off the building.

Designed to Shed Water

Every projecting course works on the same two principles: get water off the top, and keep it from running back under the stone.

• The wash. The top surface is sloped away from the wall so water runs outward instead of collecting at the back joint. A flat top lets water stand, soak in, and find its way into the wall.
• The drip. A continuous groove cut into the underside near the outer edge. Water that wraps around the front of the stone reaches the groove and drops off rather than tracking back along the soffit to the wall.
• Projection. The farther the edge sits from the wall face, the more of the wall below stays dry. Even a modest projection with a good drip keeps runoff from streaking the stone beneath.

Water that runs down a wall carries dirt with it and deposits it unevenly, which is why missing or clogged drips show up as staining patterns long before they cause any other problem. A well-detailed course keeps the face below cleaner for decades.

Joints and Flashing

The top surface of a projecting course is fully exposed to rain, snow, and ice. Its joints are the most vulnerable points in the course.

• Sealant in exposed top joints. Mortar in a horizontal, upward-facing joint tends to crack and let water in. Many specifications call for sealant over a backer rod in the vertical joints of washes and copings instead.
• Through-wall flashing. Flashing is commonly installed with projecting courses so any water that gets into the wall is directed back out. The design team sets its location and detailing.
• Metal caps on large cornices. Deep cornices with wide washes are often covered with a metal cap tied into the roofing, which protects the joints and the top surface together.
• Weeps. Where flashing is used, weeps let collected water drain to the exterior.

Supporting a Projection

Any stone that sticks out from the wall is a cantilever. In load-bearing masonry, cornice stones were proportioned so most of their weight rested on the wall, with the back of the stone (the tail) held down by the masonry above. The stone balanced itself.

Most stone today is set as cladding over a steel, concrete, or masonry backup. Projecting courses still need to be supported and held in place, but the method changes:

• Bearing. The course sits on a continuous support, such as a relieving or shelf angle, or the stone below, sized by the engineer for the weight of the course.
• Anchoring. Stainless steel anchors, straps, and dowels tie the stone back to the structure and resist overturning, wind, and ice loads.
• Multi-piece cornices. Large cornices are often built from two or more stacked stones, such as a bed mold piece below a corona and wash piece. This keeps each piece to a practical size and weight for fabrication and setting.
• Movement. A soft joint under shelf angles allows the building frame to move without loading the stone.

Fabricating Profiled Courses

• Straight runs. Straight moldings are typically run on a planer, with the profile cut along the length of the stone. This gives a smooth, consistent profile from one piece to the next, so the line reads as continuous across the joints.
• Curves and radius work. Curved cornices and belt courses on round bays or towers are shaped on CNC equipment and finished by hand.
• Corners and returns. At outside corners, the profile turns and runs back along the other face. Corner pieces are often cut with the profile running both ways from a single stone, which avoids an open miter joint at the most exposed point.
• Ornament. Dentils, modillions, and brackets add carving time. Joint locations should be coordinated with their spacing so joints fall cleanly between details rather than through them.
• Drips and washes. The drip groove and wash slope are cut in the shop as part of the profile, so they are consistent along the entire run.

Indiana limestone’s fine, even grain is what makes long runs of profiled stone practical. It holds a crisp molding edge, cuts cleanly in any direction, and carves well for dentils and modillions.

Grade, Finish, and Detailing

• Standard grade gives the most uniform color and texture along a long horizontal run, where variation from piece to piece is easy to see.
• Smooth (planer) finish is the usual choice for moldings. It shows the profile and its shadow lines clearly.
• Keep edges robust. Very thin fillets and sharp projecting edges are more easily chipped in handling and setting.
• Don’t skip the drip. A profile can look correct from the street and still lack the drip and wash that make it work. Both should be shown on the drawings.

What to Give Your Fabricator

• Full-size or scaled profile drawings of each course, including the wash slope and drip location.
• Elevations showing run lengths, corners, returns, and any curved sections.
• Backup and support conditions: shelf angles, anchor type, and any piece-size limits from the engineer.
• Ornament layout: dentil and modillion spacing, so joints can be located between them.
• Flashing and cap details that affect the stone’s top surface or back.
• Color, grade, and finish.
• Schedule for shop drawing approval and delivery.

Indiana Limestone Fabricators · 2400 State Hwy 43, Spencer, Indiana 47460