I am installing a flagstone path and was wondering if I should use Mortar or grout to fill in the gaps? Gaps range from 1 to 3 inches in diameter. Whats the difference?
You can either use a mixture of Portland cement and sand or the same crushed limestone you used for the base under the flagstone.
One of the cons of using the limestone stone base for the joints is that during a heavy rain it will have a tendancy to get washed out a little.
If some of your joints are up to 3'' wide, it might be best to use the cement/sand mixture. Although it takes a little more time and money it's probably the way to go. I've read and heard that you're suppose to wait up to a full year after setting the limestone to fill the gaps with this mixture to allow the lime stone base to settle, to prevent dips in the flagstone and cracking of the joints. You would probably be alright if you just wet the final layer of limestone base for a couple of hours with water and then re-tamp the with a vibrating plate compactor. Be careful not to over water though. Let the water soak through so it doesn't start puddling and cause wash outs.
