Cold Joints: Avoiding Costly Repairs
By Scott Cohen

In pool-remodeling work, it's very common to raise a bond beam to meet the needs of a new deck or edge detail — or simply to make the pool level again.

As ordinary a step as this may seem, it can be trickier than you might think because, in applying new, poured concrete atop the old gunite or shotcrete, you create what is known as a cold joint — that is, a space where you need to be certain you've created a good, reliable bond between the new material and the old.

Scenario: I inspected a project where a floated bond-beam addition had cracked at a point behind the tile line that was just below the water's new level. This caused a leak that oversaturated a surrounding clay soil with moderately expansive properties.

When that clay started to swell, it heaved the concrete all the way around the pool, damaged the skimmer and created a number of trip hazards.

To take care of the problem, a contractor had to come in, remove the concrete decking, pull up the coping and cut away all of the tile before basically redoing the original renovation contractor's work. All told, it was a $60,000 repair.

The Fix: All of this hassle might have been avoided had the original renovation contractor followed a few simple steps.

First, after a preliminary cleaning, he or she should have roughed up the surface using hammers and chisels. This increases the contact surface between old and new material and offers the best possible chance of subsequently establishing a good mechanical bond.

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Scott Cohen is president and supervising designer of The Green Scene, an outdoor design and construction firm based in Northridge, CA. He provides consultation for clients nationwide and gives seminars on designing landscapes, swimming pools and outdoor kitchens.