The Mystery of the Sticky Gray Ooze
An “off-ratio” epoxy emerges up through a crack in a stamped overlay.
Question:
Why did this stamped overlay crack, and what is the sticky gray material oozing from the crack?
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.
1 Comments:
Chris,
Again, great blog. In reference to the "Mystery of the Sticky Gray Ooze" topic, I think you should mention that it is critical to make sure the epoxy being used is suitable for the application at hand. There are literally thousands of different epoxies available. Of course the objective in repairing a crack in the concrete surface that is to be overlayed is to prevent the crack from reappearing and reflecting through the topping.
First know that if a new relief cut is not installed near the original crack, the crack will come back regardless of what type of epoxy was used. It my not always crack in the origianl crack but if the epoxy does it's job, it it will crack right along the original crack.
So the first question is "When should the crack be cut?" This is critical, as the substrate can move over the course of a few days if there is temperature changes or even light rain in dry climates. Therefore, if the crack is repaired today and the over the course of the next two days the coating was applied and three days from now the new relief cuts are installed, it is possible that the concrete moved and the crack as already been re-established. The solution, cut the relief cut after the proper epoxy is applied but before it cures or even dries for that matter.
Getting back to the proper epoxy... If you use an epoxy that is even slightly flexible, then the topping will crack. If you use an epoxy that is even the slightest bit brittle, the crack will recrack. Yes, there is a fine, fine line. But any ole epoxy will not do.
Finally, the relief cut must be deep enough to be weak enough to crack at the bottom of the cut before the epoxy or repaired area does.
Think of concrete as a saltine cracker. Without the perferatios, you could not control the size of the cracker when it cracked...
Keep up the good work Chris.
Kindest regards,
Ken Freestone
By Ken Freestone, at 6:54 AM
Post a Comment
Links to this post:
Create a Link
Home Page