Concrete mortar in flagstone patio?

[Richard]

The wife of course, brings this up after I've gotten to the point of being 99% done

Here's the setup and the question:

Base material is what my local quarry calls "block material". Basically same stuff that a concrete block is made of, rougher than sand finer than "rocks".

This block material base under the flagstones might be 4" deep in some areas and might be 1/2" deep in other areas. I know I have a couple stones that are set on even LESS block material. They happened to be deep stones in an area where it was already shallow.

Some of the flagstones are as much as 2 1/2" deep and some are 1" deep. Got a quote to lay all this in poured concrete and it was something like $6,000 so that wasn't going to happen since I could lay it in sand for free (since we already had the materials)

So... here's my wifes idea

dig up the mortar lines and get the current block material out of there. Get some concrete and do one of two things:

1. Pour concrete out, sweep into mortar lines and allow to set
2. Mix concrete and in essence, apply concrete mix in mortar lines like using an icing bag on a cake.

I told her that I feared the concrete over time, would crack and break out since the base it would be sitting on is block material that itself, might settle more over time. We then have the possible issue of expanding/contracting during the freeze/thaw seasons (not that we get a lot of freezing here)

So in essense, she wants to dig up all the grout lines, apply some concrete in there. I'm a bit dubious of how successful that might be over time.

any thoughts?

 

[Egon]

It'll look good for a while and then do as you predict.

Suggest a low growing spreading plant that has a nice smell to it for the spaces.

Wooly Creeping Thyme:
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[dave1949]

Ditto Egon's post. That would be a very retro look even if it did hold up. Maybe that's what your wife wants.

You might check into a mortar, lime, sand mixture. The addition of lime supposedly provides some flex to lessen the cracking. I don't really think that will help in the long run though. And the plants would be very attractive.

Dave.

 

[WayneB]

I would think trying to insert cement into the joint area would be a major task. The best way to do that is to have a cement base and set the stone down into it, not easy either.

We did about the same thing here with flat stone and had the same thickness differences which made setting the stones and keeping the surface flat very hard. I used stone dust in the joints. What I did was spread stone dust all over the entire walkway and then used a compactor to vibrate it into the joints. Then we brushed off the excess stone dust. It worked fine for us and has held up for about five years now.

At any rate you did a very nice job on the layout.

 

[polo1665]

I finished my flagstone patio about two months ago. My base consisted of 2 to 3 inches of gravel under 2 to three inches of coarse sand. My flagstones are the same thickness as yours (heavy buggers aren't they?).
I filled my joints with Polymeric sand made by a company called Techniseal. You simply sweep the sand into the joints and then spray lightly with water. There are binders in the sand that turn it hard when it dries. You will still have to remvoe the material you currently have in the joints. I think I posted a photo in your other thread on the subject, but I'll post another.
So far it seems like this stuff works good, we'll see how it fares over the winter. Cost is about $25 for a 66# bag. I used four bags to cover about 500square feet with joints about the same size as yours.

I don't think you want to use concrete between the joints unless the stones are laid on top of concrete already.

Mark

 

[EddieWalker]

The very best way to do it is to pour a concrete bed, let it dry and then set the rock into a bed of mortar on top of the concrete. You figure otu how thick your rock is before pouring the concrete so that after you put down your mortar bed, the rock all comes out flat. It's not a simple or cheap task to do it this way, but it's the only way to make sure it remains in position and the grout lines don't crack on you.

The next level down is to spread a layer of road base gravel four inches thick and compact it. Then set the rock on sand to get it level and then fill in the space between the rock with mortar. There are differenty types of mortar with different strengths and characteristiscs. I always have to look this up when working with it as I get them confused.

If you don't put in a solid base to support the rock, then you will have movement. Depending on your soil and climate, this can be allot of a little. Either way, the grout will crack on you. Once it cracks, water will get in and udner the the rock, and in time, you will have erossion. It's a local thing how fast this happens.

Just setting the flagstone on the soil and filling with pea gravel gives you almost the same result, but at a much lower expense in labor and material. Weeds growing in the pea stone can be an issue, or not. It's just a matter of spraying and killing them off when it happens. You won't have to fight the cracking mortar this way since the flagstones can move all they want and the pea gravel will just move around. The water will get in there if it rains on them really hard, so that's a maintenance issue that you'll have to address when it occurs.

Eddie

 

[hitekcountry]

What is it about the current setup that is objectionable, is it that the little bits of rock work loose and end up on the surface of the stone, or just the look of the material?

 

[Richard]

What is it about the current setup that is objectionable, is it that the little bits of rock work loose and end up on the surface of the stone, or just the look of the material?

Yes, it's the little bits of sand that roll around & get tracked into the house by the dogs (six of them) or us.

This sidewalk was installed by me maybe 8 years ago. I then had to pull about 1/2 of it up (along with scooping up most of the underlying block material) so we could do the addition. Once the addition was done, I had to start laying it down again. I bought an additinonal 4+ tons of flagstone and another 6 tons of block material.

Today it's essentially done (save some smaller filler pieces that need to be cut to fit) and now she's talking about ripping up the grout lines.

Although I don't think it's ever going to happen, what I really thing is going on is she's either trying to drive me insane or give me a heart attack from doing the same sidewalk repeatedly.....

I didn't really think the concrete grout lines would hold up over time and have told her that. By asking here, I get some other unbiased comments that might (and sometimes do) show me to be wrong or perhaps in this case, help substantiate my comments to her.

I think she's now put aside the idea of grouting with concrete.

Side note.... I DO think it would help if she stopped spraying the grout lines with the hose in blast mode..... she keeps wondering why we have sand everywhere and why it keeps coming out of the lines and all our lines are void of 'grout'.

I look at her with the spray nozzel or the blower and just gently shake my head....

 

[dave1949]

Ahhh.

I think the polymeric sand suggested by polo1665 is the best solution now that I know what you are trying to achieve

We have the same problem and the concrete paver supplier suggested the same thing. It might cost a bit for your wider grout joints, but that old gritty feeling inside should go away.

Dave.

 

[RobertN]

Ditto. Did this on a walkway for my Mother in Law.

If you grout those spaces, it will eventually crack. They do make for nice polymer grouts now that would last longer...

The only way for a real solid long lasting installation is pour a pad, set the rock in mortar, and grout.

Clean out some of those joints and put some ground cover in.

Suggest a low growing spreading plant that has a nice smell to it for the spaces.

Wooly Creeping Thyme:
Woolly Creeping Thyme Herb Plants | Wooly Thyme