[Chris Heiler]

This one is for all you hardscape experts out there.

Let me give you some background.

I was the designer and general contractor for this installation about 3 years ago.

My mason installed 3/8"-1/2" slate on a concrete base with snow melt. The snowmelt was used under this paving ONLY in the front yard. We also used this slate on a concrete base in the backyard WITHOUT snowmelt.

This spring we now have serious issues with the slate that is installed over the snowmelt system. Many of the pieces have come loose and the whole walkway has kind of a "hollow" sound when you tap on it.

In the backyard, where there is no snowmelt under the slate, everything is perfectly fine.

My feeling is that the snowmelt system must have been turned off at some point or just wasn't working for a short period of time and water seeped in and froze.

Anyone have an experience like this before or have any thought as to what might be the issue?

Here is a photo of the front for context. You can't see the damage by looking at this however.

[Stonehenge]

I don't know of a situation exactly like that, but I would expect that it could be caused by a few things:

Conditions in front and backyards are different - possibly more sun in front (though it doesn't look like it), melting the ice and refreezing at night.

Salting the front walk may have contributed as well.

The ice melt system could have been selectively operated through the winter, creating many more freeze-thaw cycles than a paved surface would normally see over a winter. It's the incremental freeze-thaw behind retaining walls that kills so many of them, and it could be reasoned out that this would be a causative factor here, too.

The wrong mortar could have been used - Type M is going to be best for this application, and if another type was used, freeze-thaw created by the ice melt system may have hastened the failure.

That's my $.02 on the issue. I don't envy you on getting this situation resolved.

[Chris Heiler]

What effect does salting have Jeff?

[Stonehenge]

Salt can work to deteriorate mortar, but I was thinking more about the potential for freeze-thaw when using ice melters.