[jwholden]

I was talking with a friend yesterday and we discussed the patio I am working on it the thread 'Mixing concrete is cold weather'. He asked how I went about installing bluestone and I said 3/4 process base with stone dust for the last couple inches to set the stone in.

He asked if I ever tried installing bluestone on top of process set in an inch or two of cement. He said it is MUCH FASTER than using stone dust because you set the stone down once and tamp it to level rather than lifting to add/remove stone dust. I think I saw pictures of the Roger Cook on This Old House do it that way as well. It seems to me that this method will look great when installed but become a mess once a few winters pass and be a royal pain to repair.

Has anyone ever tried this method of installing bluestone? How has it held up?

[Bill Schwab]

J.W.

One thing to consider...All concrete carcks, and it does not necessarily follow the grout lines....

[Stonehenge]

Yep yep. What Bill said. And with an inch or two, count on many cracks.

If you do it that way, I'd only offer the 'tailight guarantee.'

[Lanelle]

The only thing that method guarantees in cold climates is a job of regrouting it every spring. I work at a site with that type of installation and the repairs are nearly constant.

[PSUscaper]

If your gonna use concrete, then I think you will need a much thicker base than that.

Most wet laid blue stone starts with a 4" + reinforced slab, and then a inch or two of mortar to set the stones in.

Also, be carefull not to use the 'dab' method. Some guys take a trowel of concrete and put in on the ground at the four corners where the stone will set and then press it in.

The problem here is.....especially if you are using thinner stone, is that you create four pressure points under the stone and run the risk of the stone cracking as pressure is applied to it. Kind of like laying a flat rock on top of flat concrete but leaving a small pebble underneath it.

But............i will have to say this.

When you think about the installation of dry laid blue stone, you have to wonder if adding concrete underneath really changes anything. I mean, they are sitting on dust/sand, so really, how is concrete going to change anything. If they are going to heave, does it matter if there's concrete underneath it or not.

I will say that I would not joint the stone with concrete as one has previously stated, but have a hard time deciding for myself that if I am going to use dust in the joints, and that the concrete will speed things up, is it really a bad thing overall????

[agla]

JW is talking about using a 2" cement mud base as an installation process. The idea is to be able to set the bluestone onto the mud and bang it down to the proper height. There is no slab and there is no mortar joint. Stone dust is swept into the joint afterward. This is used to speed a dry laid installation and avoid voids beneath stones.. It is not meant to create a monolith, but to set individual stones.

I have not done this with bluestone, but it is a common technique for cobble borders and aprons where I'm at.

[BJR]

I agree with agla.

I install sandstone the same way.

We bed it into a mortar bed on roadbase. If we have cut the stone to have a 2mm joint we sweep in sand. If we have not cut the stone and it has random gaps of up to 25mm we use a small decorative, angular, gravel for the joints.

Bedding it into mortar definately speeds up the process and gives a firmer finish.

[Stonehenge]

So it sounds like you're accepting the slight cracking (except maybe for you BJR, where it never freezes...), with the idea that it's already a very thin mix. Or is it?

Is a bag of mortar or cement just mixed in with some 3/4" stone and wetting it, or are you really pouring a thin slab?

[Bill Schwab]

With the expansible, hard draining. non perculating soils we have here, the only way that might work is if we packed a 6" base and used it as screed. Interesting concept though, this has been very informative

[jwholden]

Jeff,

I don't think you're asking me, but, it sounds like the bluestone are set on top of the 3/4 process in the EXACT same way you installed your brick on top of the concrete slab. Just a little cement and tamp the bluestone in. Don't fill the joints between the slab, simply sweep in some stonedust.

When I think about this more I have seen a mason around here use a similar method to install a fieldstone patio, though he put mortar in the joints as well.

I'll have to see if I can find Roger Cooks E-mail...

[agla]

I think you only put cement mixed with sand (not concrete) under individual stones to set them on the normal dry lay type base. The idea is that it takes up the gaps and allows you to push it down to grade (rather than scaping out, adding a little here or there, and still winding up with voids). The cement bonds only to the bluestone allowing it to move with freeze thaw just as if it were all one piece of dry laid bluestone.

I caught the very end of that segment on This Old House. All I heard was Cook recapping to Tommy Silva or someone else, but the video of the work was already over.

[jwholden]

The cement bonds only to the bluestone allowing it to move with freeze thaw just as if it were all one piece of dry laid bluestone

When you say it like that it sounds like a great alternative.