Mortar Bedding For Stone On Concrete Question.

lukachuki

Ok I have a couple of questions about laying stone on concrete. We just did a patio that did not come out to well and so we are redoing it. I chose this time to use a recipe for the jointing that I picked up here on CT about a year ago. Well all the joints are failing so my guys today are grinding them out and I will go back to my bagging method which has worked real well over the years. Now let me say that I don't think the advice was bad we just didn't do something right. I figure that either we didn't get quite enough water in the mix...what is crumb cake anyway....or we didn't press in the mix firmly enough. In any case it is all crumbling out of the joints so we are replacing all the joints today. Here is the quote from CT that I used in jointing this stone.

My first question involves the joints themselves. We are grinding and chipping out the crumbly mortar and just planning on going back and bagging w/ a 3/1 sand portland mix wetted down to flow through a bag and then after some setting cut flush. This is the mix we have used with success but never in a retrofitted joint. Anyone see any problems?

Second question. What do you guys bed your rock with? On this job we just used type N mortar built up about 1". I know the rule that you don't want mortar which is harder than the surface to which it bonds but what do you guys do? Do you add lime or use a portland mix? This stone is real soft and thin which I know is a bad combo but I have no choice in the stone selection process. This type n mortar did not work very well as the stone did not adhere to the mortar very well.


Thanks,

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Tscarborough

That is a good mix for making concrete block, but it is hard to get sufficient vibration and pressure to make it work on grouted joints. Cement requires water for hydration, and the less water used the more through mixing and consolidation required. I have used a crumbly mix of non shrink grout for dry packing baseplates, but it was mechanically mixed and packed in thin layers.

Most guys I know just use regular type S mortar (mostly portland/lime) when laying the stone and grouting the joints.

edit-Me, I am allergic to mortared in flatwork. I stick to SCP systems.

stacker

i have always used the same mortar for laying the stone or pavers as i do for grouting.i have never had a problem.

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lukachuki

neither have I until recently....do you use s or n?

__________________
"The problem with internet quotes is, you never know if they are authentic." -Abraham Lincoln-

Less with the jaw more with the paw!

stacker

most time type s.its about all out lumber yard carries

__________________
life is short,do your masonry naked!!
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Tscarborough

Flatwork is not the same as wall work. Compressive strength actually matters, although bond and flexural are still paramount. I always recommend lime (type S, not ****house) because it will self-heal small cracks, plus it is an excellent air entrainment agent. Mix well. Mix well. And just to repeat, mix well.

jvcstone

I've developed a fondness for painting the slab and the back side of the stone with that latex concrete bonding agent-- about a 50-50 mix with water. Tile setters thin set will also work. Have not had any bonding issues since I started doing it. Be carefull not to slop it on the top side as it will dry with a glossy look. I use a type S mortar mix for bedding the stone, and also grout with the same mix as I go.

JVC

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tkle

I'll generally use thinset for buttering the backside keeping a bit away from the edge so I can grab it without getting my fingers dirty.Set the whole stone at once so there's no voids.Tool your joints so the stone edges are packed.Grout the next day with 1 part 60 silica sand/2 30 grit ss/1.25 common cement.Parge,sweep,sponge,sweep,then final sponge.

Dik Redi

exactly tscar ,, you need some lime to make the mix creamy to flow throw the bag,, and crumbly thru a bag ? your wrists must be a reck,, ( maybe i miss read ))

Dik Redi

besides the other advantages of lime

Dik Redi

That crumb cake mix you mentioned with the hand squeeze,, i use that mix on stone walls,(( no lime tho)) and not thru a bag,,make a meatball in your hand should just stain hand (dampen hand) thats it, if i jiggil it a bit and it gets to soupy for me`taste,, sending it bak lol