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The Mystery of the Sticky Gray Ooze

By Chris Sullivan – ChemSystems, Inc.

Question:

Why did this stamped overlay crack, and what is the sticky gray material oozing from the crack?

An "off-ratio" epoxy emerges up through a crack
in a stamped overlay.

Answer:

The crack in this stamped overlay is caused by a crack in the underlying concrete that reflected through to the overlay. The sticky gray material is the epoxy that was used to repair the original crack.

The original colored and stamped concrete slab had developed cracks running through about 30% of the slab. The contractor decided to use a stampable overlay to cover the slab instead of removing and repouring the concrete. After preparing the surface, the contractor used a two-part epoxy to fill and bridge the cracks. But the epoxy was not mixed in the proper proportions (referred to as "off ratio") and thus never fully hardened. The soft, sticky material has no ability to bridge cracks. Instead, the crack reflects through to the overlay and the epoxy then oozes through the surface crack.

The repair involves using a strong chemical stripper to remove the sticky ooze and then filling the crack with a caulk or grout in a color matching the overlay. Chances are the crack will always show, but a good color match can minimize its appearance. Tape off the repair area to reduce cleanup and protect the adjacent surface. After the caulk or grout has cured, seal the entire area as normal.

Always read the directions carefully when working with any two-part epoxy compound. These chemicals are designed with tight tolerances and ratios. Failing to properly mix the correct amounts of material can lead to failure.

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