How to determine if old plaster is under new surface


New member
May 2, 2012
Our in-ground pool (approx 15000 gallons) was originally constructed in 2012. The original plaster surface had extensive surface crazing, and the builder agreed to resurface with new plaster the following year. The 2nd layer was applied with bond coating/partial chip out. This 2nd plaster layer failed with significant delamination in 2018.

At this point, we hired a company specializing in renovations to re-surface with a pebble finish. A full chip out was strongly recommended for proper installation of the new pebble surface, and we paid extra for it. Today, 3 years after resurfacing, I noticed a severe linear crack about 6 feet long. After investigating the source of this crack, it was determined that old plaster that was delaminating was found beneath the pebble finish. Since this was a breach of contract (they failed to do a full chip out), the pool renovation company will likely fix the affected area at their cost.

My question is: how can I determine if there is old plaster under the pebble surface in other areas of the pool (which may eventually fail in the coming years)? Obviously, I don't want to have to deal with repairs every year!


TFP Expert
Mar 2, 2011
There might be a way to do some sort of ultrasound test, but that would be difficult to find anyone who could do it at a reasonable cost.

You could do some core drill samples to see what is below the surface, but that will leave holes in your plaster that you would need to patch.

Since they’re patching anyway, they could patch the holes at the same time.

You would need to drain the pool to use a regular drill or you could use a pneumatic drill under water.

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