Exterior Stair Joint Repointing: Sealant vs. Mortar

By: Nicholas Colefield

While we might admire an ornamental railing, or pay brief attention to the depth of the treads or the height of the risers, we typically see a staircase as simply a means to our destination. No one really thinks about the joints between the treads, which are extremely vital exterior staircase components. If not properly sealed, water can infiltrate these joints. The resulting cracks and upheaval in the treads can turn any staircase into a safety hazard. There are 3 options for properly sealing these joints, and each method has advantages and disadvantages.

Pointing joints with mortar is the most traditional method of staircase preservation.  The existing mortar must be cut out to a minimum ¾” depth. During repointing, the new mortar must be tightly packed in thin layers and then tooled to a smooth concave finish. This allows the new mortar to properly bond to the staircase. Mortar has a long life span, and is able to withstand a great deal of abuse without failing. However, mortar is a porous material. Over time, small amounts of water infiltrate the mortar, making it susceptible to cracking caused by the freeze thaw cycles common to this area.

Using sealant as the primary repointing material is becoming more common in the construction industry. The installation process is similar to that of mortar. Although, unlike mortar, sealant is an impermeable material. Water will not be able to penetrate any deeper than the surface of the sealant, making it almost invulnerable to deterioration caused by freezing and thawing. A major drawback to the utilization of sealant is that it is not capable of taking as much abuse as mortar. If sealant is installed at a staircase where there is a high volume of pedestrian traffic, the sealant will only last a few years. Additionally, if a staircase is regularly exposed to the sun, sealant will dry out and crack.

A final method for repointing these joints involves a combination of mortar and sealant installation. The existing joints are properly cut and repointed with mortar, and a bead of sealant is then installed over the mortar. The durability of the mortar and the impermeability of the sealant combine to significantly extend the life of the staircase joints. Since it’s still exposed to pedestrian traffic and sun, the sealant will inevitably break down as the years progress; however, the mortar that has been protected from the freeze-thaw cycle of water will be in excellent condition. Since additional materials and man power are required to repoint the staircase joints, this combination method is costlier.

Even though staircase joints often go unnoticed, their impact on the condition and lifespan of a staircase is essential. Property Owners should consider factors such as: traffic volume, location, exposure to the elements, and restoration budgets, when determining the best preservation options for these critical staircase components.


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