Hi,

My wife and I decided to tear down a flagstone patio. We asked our contractor whether the stone could be re-used in future projects. He replied that only 10%. I decided to try the demolition myself in the hope of saving more. The work went surprising well, far beyond my expectation.

The patio was 12 years old. It had a concrete foundation, and the flagstone pieces were attached with mortar. After I broke up the grout with a demolition hammer, whole pieces of flagstone became loose. In fact, often I did not need the demolition hammer. I just jammed the claw of a hammer underneath the pieces, pulled on the handle several times, and that was enough to lift the flagstones and beak the grout.

Is my experience normal? Shouldn't the mortar bond the flagstone to the foundation tightly? Or did the guy who built it do a bad job? I have another patio built by the same guy. If he screwed up, I will replace the second patio the first chance I get.

Thanks for any tips.

William

Sounds like a classic example of a too-dry mortar mix when attaching the flagstone to the patio. Anytime you use a mortar or thinset mix as a bonding agent on concrete and a porous stone, some of the moisture in the mix will be absorbed into the concrete and flagstone. If the mix is too dry to begin with, then too much moisture will be leached out and the mortar mix will become more powder-like. It will still bond, but the bond will not be very strong as there is no 'grip'.

If you want to test your other patio for this without destroying it, then lightly tap several of the flagstones with a hammer. Stones that are not attached well will make a hollow tapping sound while those that are secure will sound more solid without echo.

Jaybee,

Thanks for the explanation.

I also tested the other patio as you suggested. I found several pieces of stone that sound hollow, plus several more that feel loose when walked on. I guess the patio won't last more than a few years.

On a related subject: how do I prepare the removed flagstone for new projects? Will the old mortar cause any problems?

William

You need to remove the old mortar - or at least any mortar that adds thickness or lumps. As you could imagine, the more uneven the underside of the flagstone is the harder is is to get it level. Probably just some simple chipping with a chisel or flat edge of a masonry hammer will do the trick.

Definitely need to remove all old mortar sticking to the outer edges that may be visible on the new install - no way will the old mortar/grout match up with the new.

a tip from the ages... don't apply mortar to dry block. it won't adhere. spray the block periodically with a hose so the mortar is not slaked by the block into dust.

any mix containing Portland cement strengthens as it "dries," actually cures, because it draws in water and locks it up in the crystallization of the cement.

so if you start with dry block or brick, there's nothing to make the mortar rough and tough there.

Thank you for the tip. I will keep an eye on rocks when I get started.

William