Need some input. When doing a flagstone overlay on top of existing slab/sidewalk,  what is most popular when getting control joints in? So, you have concrete sidewalk with screed key or control joints, then how do you mimic the same on top with flagstone? What method is most used? This will be NE region with freezing and thaw cycles. I’ve heard where masons use western red cedar, I’ve heard of masons cutting them in and I’ve heard of not using any which is prone to failure. We all know what they do in Florida doesn’t work in NY, Maine.  What is best in keeping everything floating and most importantly keeping water out of control joints? Thank you.