View Full Version : Flagstone/Cobblestone on top of concrete patio
04-18-2006, 04:19 PM
Please advise, I want to install either flagstone or cobblestone on top of an existing concrete, in good condition, patio. What's involved in this?
04-18-2006, 08:09 PM
Normal install for the flagstone, normal procedure. Stiff mortar mix, grout with a bag and work the joints, clean off and enjoy. Pattern flagstone or irregular will work out fine.
04-18-2006, 09:31 PM
If the existing concrete is in good condition......clean it anyways. Go to your local hardware store and buy some muratic acid....its very cheap and dangerous!!! Mix is to specified rate for masonary applications. One you clean it, you should prime it with a acrylic bonding agent to alow the mortar to adhere better. At the very minimum you should wet the concrete so it does not take all of the moisture out of the mortar. You should also do the same to the stone. I prefer acrylic bond because it also has added benefits such as better crack resistance in freeze/thaw cycles. We also mix our mortar with acrylic bond/water mixes. Its not cheap....but worth it. try to point your joints as you go so that the base mortar and jointing mortar are one, and not a cold joint....dont slick your joints right away....wait a little untill the mortar stiffens up a bit...this will keep your stones cleaner as it wont allow the wet mortar to smear up on the stone. If the existing concrete is pretty smooth, you might want to think about cutting small lines in it with a concrete saw about 1/8-3/16" deep and spaced out every 1.5-2" to allow the mortar to grab on to the existing concrete better. Another thing to remember when you are doing your steps , if the step attaches to a different surface such as asphalt, grass, interlocking etc.... dont butt the flagstone right up to it, keep about a 1/4-1/2" space and fill it with a foundation caulking. This is to prevent the other surface in freeze/thaw cycles from pulling or pushing your stone and popping it off. Keep all your jointing space consistant, watch that no lines rum through for to long of a distance amd take pride in your work!!!
Also..use type s masony cement, and make sure to use brick sand because it is finer and leaves a less porus joint than concrete sand. 3-1 ratio sand to cement.
Hope that helps!
04-18-2006, 09:50 PM
One more thing...remember that any exposed cut edge should be faced by striking it with a facing chisel. Take your chisel about 3/16" back from your sawn edge, slant your chisel to about a 80 degree angle and strike it, creating a chipped edge, you must flip over the stone and strike it from both sides so you get a "belly" to the chiseled edge. If your chiseled edge fails to get a smll piece in the middle of the sawn edge...dont panic...grab a torch and pint it towards the "missed" spot for a couple of second, and depending on the stone your are using it will pop off. WATCH YOUR ARMS AND EYES STONE IS HOT when it pops off onto you. Your first job wont be easy.....but you CANNOT rush it...IT WONT come out good!!!!! Be patient, dont expect to make alot of money on your first one because time will kill you! Do it right and I GUARUNTEE that work will follow, a good mason is VERY hard to come by and are always in demand! Dont mix your mortar to dry, it will be harder to level your stone that way! Not to wet or your mortar will be weak! Allow for a minimum of 1" mortar down. and no more than 2". I usually put down 1.25". If it is very hot out once you are done or if you see the jointing mortar is drying to fast get burlap, wet it and lay it over the area..this will slow down the drying and keep it from cracking the joints.
Once again TAKE YOUR TIME!!!!! ITS NOT GOING TO BE EASY, BUT IT IS VERY REWARDING!!!
We charge about $40.00 /square foot on a existing concrete patio when the stone costs about $11.00/square foot.
A 10' x 10' area will take us about 6 hours to lay, but for a first timer I wouldnt be surpised if it takes 3 days to get it perfect!
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