[fakie99]

we've installed our mortared bluestone/flagstone on 6" compacted gravel bases in the past. a prominent stone supplier here recommends this method. I have however heard of guys laying mortared stone on concrete pads, which of course sounds a lot sturdier. what are your thoughts on base prep for mortared flatwork? (we are in Michigan, so frost/freezing is a big concern)

thanks,

jim

[Stonehenge]

Jim, prep it like you might a paver walk or patio, except that having a perfectly flat prep isn't as critical; the concrete will fill in where it needs to.

Keep in mind the concrete WILL crack, and take the advice of others here who will advise you to plan your concrete relief joints and bluestone seams carefully to allow for that cracking.

We've been tackling more and more mortar work, but that's mainly because that's my next 'mountain' ("Why'd you climb that mountain?" "Because it was there."), but I think you'll install it faster and have a smaller chance for headaches and callbacks doing it the way you've done it in the past.

That's my $.02, anyway.

[fakie99]

thanks for the reply. ( ihear you on the mountain tackling when choosing jobs - it's been my curse for a couple of years now )

so it sounds like you have been laying mortared stone on a mortar bed, supported by compacted gravel bases? how about the durability - you and I are in similar climates it looks like. ...

[agla]

Pavers are prepped in such a way because they move with freeze thaw. if you mortar joints and things are moving with freeze thaw, the result is that something has to give. Even if you do this on a slab, the slab has to have control joints if the size and shape of it merit it. Then you don't span the control joint with stone or mortar. There is a flexible joint material called Deco-Seal that you can get in many colors that pours into the joint and looks like a mortar joint, but is water tight.

[Stonehenge]

The paver/stone mortar work we've been doing has been over a concrete slab. So we excavate, prep for concrete, pour concrete. After it sets up, we place stone/pavers/etc on a bed of mortar and mud the joints, too.

I should say that this method will neve become our primary method of install; dry-laid is faster, and done right, it's better, too. But over the years I've been trying to expand the hardscape offerings we have, and this is one area we've been expanding into.

[fakie99]

i see - well let me ask you this: when you began doing the concrete prep-work, how involved was it. i have learned my lesson about getting into other lines of work as a landscaper (irrigation, concrete, decks, etc.) and I'd just as soon sub the concrete slab out. but i'm having a hell of a time getting good subs who are willing to do the work. so, if i were to tackle it, what am i in for. i am assuming you prep the forms, have concrete brough in by truck and float/finish it yourself? i'm nervous to trust myself on this....

jim

[Stonehenge]

It's actually pretty easy. You don't want any kind of finish on it, otherwise it'll be less 'sticky' when it comes time to mortar. So excavate, compact a couple lifts of stone like for a dry-laid project, form it up, lay in some reinforcements (rebar, mesh, whatever), order up the truck, pour, and strike it off.

[Bill Schwab]

Can someone please learn me sumthin here....

Why, in areas where there is frost, snow, ice, rain heat and what I see as the most exteme elements, do bluestone and flagstone patios get laid on 1" minus gravel then leveled in sand, then mortared? How can anyone expect this to be a permanent patio?

Here where we get little if any snow, never heat over 85°, and less than 3" of rain a year no one does blue stone like that. What is usually set is gauged, random cut bluestone, on top of a 3 1/2" six bag mixed concrete patio, with #3 rebar on a 24" grid, thin set, or moratered down to the top. Control joints are placed where grout lines will be so when the base cracks, it only cracks the mortar. So, what the heck makes these types of contruction work where the elements are the most extereme?

[agla]

I agree with Bill. That is exactly what I was trying to say.

[Lanelle]

The only reason that I can think of is job security. Once a patio has been laid on gravel and mortared, you are assured of annual re-pointing jobs.

[BJR]

You woulden't put pavers on a sand bed then grout the joints. What's the difference?

[Stonehenge]

Hold on a sec - I think I may need to clarify something. I'm not saying that any mortar should be going on where a modular pavement (hope that's the right term) is being laid on crushed stone or sand. Is it somehow coming across that way?

Here's a graphic of what I'm trying to say:

[fakie99]

yeah, i get it, but why crushed stone under the concrete as opposed to regular sand? sturdier yes, but necessary?

[BJR]

The crushed stone helps to buffer any movement in the underlying ground. It also makes sure you have a firm base.

Stone, I understand what you are saying, but I just can't believe that anyone would contemplate laying a mortared modular pavement over a stone base. It might work in places in the US, but it sure doesn't work here in Aus.

[agla]

If your subsoil is sand (like here), you won't need the crushed stone. If it is clay, you should use it.