threashold crossing

[machmeter62]

I have a 4"x4'x16' (with rebar included) concrete courtyard crossing that is now ready for covering in natural multi shaped relative flat stones. My concern is what type of bonding should be used for maximum strength to prevent the stones from popping loose from the weight of vehicle wheels.

Is Type S masonry mortar strong enough for the bonding to concrete slab, or a mixture of Portland cement better with smaller gravel, or maybe another method better? I just don't want to do this twice? Thank you in advance.

 

[rus_geek]

What type of surface are you crossing from/to ? Where are you -- do you have to deal with frost and/or ice? Is this a decorative crossing, or functional? My first instinct is to bed them in sand and not bond them tightly to the concrete.

-rus-

 

[machmeter62]

The location is a mild climate in Northern Calif. We do get occasional freezing weather, but not a deep freeze. The slab size is to accommodate large propane or septic trucks if required in the future, but may never be required? This decorative entrance is to enhance the two swinging eight foot gate fences to deer-proof the courtyard, which was completed in the 90's. The stones will be placed on a very firm concrete slab, but the bonding must be suitable for heavy traffic.

 

[GE222]

Right idea, but I would not recommend sand to bed them in due to the instability of sand. Instead, consider crushed limestone as it will pack together with a much more solid base.

 

[Gary Fowler]

Regular sand / portland cement grout will work for you. You can make your own or buy it dry mixed so you just add water. Dont add too much water; that will decrease the strength and dont mix up more than you can use in 30-45 minutes as it will start to set fairly quickly. Just make sure that your stone and the concrete is cleaned of dirt and grease/wax so the portland cement will bond to it. A concrete bonding compound will help the grout to adhere to the concrete and stone also. If it is weathered a bit, you may want to lightly grit blast it or acid etch it to remove the laitance and or dirt prior to bedding your stones on top of the concrete. You can also get the portland cement in white or grey or color your own if you want exotic colors of grout. The colorant is rather expensive though.

 

[machmeter62]

Regular sand / portland cement grout will work for you. You can make your own or buy it dry mixed so you just add water. Dont add too much water; that will decrease the strength and dont mix up more than you can use in 30-45 minutes as it will start to set fairly quickly. Just make sure that your stone and the concrete is cleaned of dirt and grease/wax so the portland cement will bond to it. A concrete bonding compound will help the grout to adhere to the concrete and stone also. If it is weathered a bit, you may want to lightly grit blast it or acid etch it to remove the laitance and or dirt prior to bedding your stones on top of the concrete. You can also get the portland cement in white or grey or color your own if you want exotic colors of grout. The colorant is rather expensive though.

Thanx for the info Gary,.... this is probably an over-kill, but I didn't want to do the same job twice. I have followed all your advise, and where the heavy traffic area is, I used that 5000 psi cement, and getting good results. My only question...how long before I can drive a standard vehicle over it? I have been told a week to ten days is adequate time.