Flagstone over existing slab with expansion joints in place

I bought the DVD and found it helpful, but I did not see this addressed in the video or on this site. I have a 650 sq ft project in mind. The slab is 8 years old and in good shape. It has expansion joints in it per code and is bordered on 3 sides by the foundation. I plan on leaving a half inch all the way around between the stone and the foundation and caulking there. How do I handle the flagstone where it crosses the existing expansion joints? Do I go back after the stone is in place and cut expansion joints in the stone to match the underlying expansion joints in the slab, or do I just let it be and fix the grout between the stones later if it cracks? Thanks

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Lay big pieces of flagstone over the expansion joint
by: David

Where ever you have the expansion joints in the middle of the slab, try and cross that with big pieces of stone. Then keep watching it over time and see if you're beginning to have hairline cracks in the cement joints between the stones. If you do get them, take a demo saw and cut deliberately through the stone where the expansion joint is. You don't need to make the joint any bigger than the saw blade.

After you cut the joint, you can caulk it, but it really doesn't look good.

Hopefully you won't get any hairline cracks and you won't have to deal with that.

Great luck,


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