Telephone tile was used for foundation construction in the early 1900’s. We have found it to be most prevalent in homes which were built north of Chicago and close to Lake Michigan. They were constructed by using mortar to bond the telephone tiles together as they were stacked. The type and strength of mortar used at the time the wall was constructed is always questionable. As these foundation walls age the mortar deteriorates (turns to powder) and the walls lose strength, possibly causing them to develop cracks and bow inward. The inward bowing is caused by the lateral or horizontal earth pressure pushing the weakened foundation wall inward. Lateral earth pressure increases significantly as the soil becomes saturated with water. With these older telephone tile foundations the problem is made worse as perimeter drain tiles were rarely installed. This is usually evident as the basement area may be wet.
If the mortar joints are deteriorated but the foundation wall is not cracked or bowed, and the objective is to simply extend the serviceable life of the foundation walls, then the solution may be as simple as cleaning and tuck pointing the mortar joints. If water penetration is an issue, then the exterior may have to be excavated and a perimeter drainage system installed. At the same time this is done, the exterior of the telephone tile foundation walls should also be cleaned, tuck pointed, and water proofed. Care must be taken when back filling the telephone tile foundation walls so as to not damage them with the impact of the back fill material.
If the foundation wall has bowed inward slightly, and the mortar joints remain intact except for a single horizontal crack, and a couple of diagonal cracks at the ends of the wall, then it may be possible to stabilize the foundation wall by bracing it. The most economical and effective way to brace a telephone tile foundation wall is done with vertical steel beams. The vertical braces rely on the foundation wall having enough integrity to resist the soil pressure and span from bracing beam to bracing beam which is the reason for not have numerous mortar joint cracks.