Pavers Over Concrete - My Cousin's Method

Tommy C

Fellas,

I'm going to describe how my cousin does paver patios, walkways, and driveways. I've done it this way a few times as well, with no problems. Has anybody else done it this way...or do you guys see any problems with the method?

- Excavate the dirt to 7 inches below grade, tamp soil well.

- Spread crushed stone about 1 inch thick as a base.

- Pour 4 inches of concrete, reinforced with grid wire.

- Bullfloat it, and finish it to a smooth finish with steel trowels.

- Let set up nice overnight.

- Next day, lay pavers out in desired pattern, directly on top of the smooth slab.

- Cut outside pavers, in place, to allow for a border.

- Borders are then glued down with a small amount of thin set, to the slab.

- The edges of the borders are parged with fortified mortar (so sand stays in)

- Stabilize-O-Sand swept in and activated with water.

Your thoughts?

The only possible problem I see, is that on the end of the patio where the water is pitched towards, water can collect underneath the pavers, and be trapped there because of the parging on the ends of the pavers. If it freezes, that collected water (although it's a small amount) will pop a few border pavers off from the thinset bond.

neolitic

That was my dilemma awhile back. I've seen a lot of pavers on slabs that have popped from freeze, but who knows how they laid 'em. I know that one we took up was bedded in mortar, but no one knew how old it was.

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Tommy C

See in this method, the pavers are laid directly onto a hard slab, no cement, no glue. It's only the borders that have a bit of thinset. The borders are therefore the only thing at risk of "popping"...but it's not as if they are going to go far if they do.

neolitic

At that point I wonder what good the slab really does for you? Why not just a good gravel and sand bed, that you know will drain?

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neolitic

I'm no expert, just thinking out loud.

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concretemasonry

That is definitely NOT a recommended method!! - Your cousin probably has been lucky to get away with it for most common pavers. There are many potential problems.

What type of pavers? The most common(interlocking concrete pavers) or clay pavers?

The concrete slab subjects the pavers to the freeze/thaw deterioration and traps water that can lead to poor support. Pavers laid directly on a slab will eventually rock and crack due to uncompacted sand being washed under them.

With concrete pavers that have the greatest strength and flexibility, the recommended method for a patio is to place 4" to 6" of road base compacted to be parallel to the finished grade. Spread 1" of concrete sand and level without compacting. Lay the pavers in the sand setting bed. Install a paver edging/restraint (concrete units, plastic, steel, aluminum) securely anchored. If the edges are curved you can install the edge units either before or after sawing. Spread a layer of sand over the paver and vibrate to level the pavers and create a good interlock between the units.

This is the standard method of installation. The difference if you are building driveways, streets, airport taxiways or heavy duty industrial pavements would the the thickness and compaction of the road base. No cocnrete slabs are used in proper concrete paver installation.

If you are using clay pavers, the may be some deviation depending on the climate if you want the pavers to stand up to the weather.

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Dick

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Tommy C

Neo,

What the slab does for you, is provides a glass-like, smooth surface, with the desired pitch. You just throw the pavers on...it is very very fast. Also, the pavers will never sink, as long as the dirt below the concrete is tamped well.

neolitic

Screed the sand, and it does the same without the problems. And saves the price of the concrete.
I believe Concretemasonry.......most of all 'cause he agrees with me

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dirt diggler

yeah - your "cousin" doesn't sound like much of a paver guy


for one - why pour concrete when you don't have to??


you do know that you're supposed to tamp the stone base, right?? (You do not have a stone base - you have concrete)

sounds like your method is to just save time when it comes to your slope/drainage.

you can do this while you're setting the pavers (with a stringline).

So there's no reason to have concrete enter the picture.




I'm not even a paver guy ... but I think if you're doing this professionally (pavers) - you need to talk to some manufacturers about some training courses

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Tommy C

Concretemasonry,

I realize that the method is not what is recommended. But I'm hard pressed to find evidence that the patio/driveway/walkway would not last. The pavers that are not glued down will not pop, because they laid dry on the slab. Where are they gonna go?

concretemasonry

You can choose your installation methods, but you cannot choose your relatives.

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Tommy C

Hey Dirt Diggler,

What happened, did you have a bad day today?

Pavers are one of my specialties...I do a whole lot of pavers. And I typically do it in the standard method, as concretemasonry described. I come from a family of masons...just about every male on my mother's side of the family is a mason. My cousin, who does very nice work, started doing pavers with this method a few years back. His jobs have come out beautifully...it really is a lot quicker, too. So I did a few jobs with his method this fall, and it went well.

I came here to ask some of the professionals on this board their opinions on this method. I knew that some people would be opposed to it...but I think I can defend it, so long as there is some escape for the water on the side of the patio where everything is pitched to.

woodmagman

I have seen this done on City cross walks....were asphalt ties into the paver. I thought it may have been done like this due to the heavy transit bus traffic. I believe they screeded a coarse sand prior to paver install and plate tamped after the paver was installed....I do not recall the concrete being much more then bull floated.

concretemasonry

The first question is - What kind of pavers are being installed?

If you have clay pavers, there are several different methods depending on the application/use, type/style of paver and clmate.

Most pavers used are interlocking concrete pavers that should be installed in a manner similar to my suggestions. Look at the site for the Interlocking Concrete Paving Institute (icpi.org if I remember right). They certify contractors and have a good site with many publications on design and installation of concrete pavers.

In general, the highest load carry capacity pavers in use are interlocking concrete pavers that are installed on a compacted base and not on concrete (for aircraft and industrial straddle loaders at ship unloading facilities). Concrete causes problems with pavers and increases the cost without increasing the strength.

One of the main reason (in addition to appearance) for pavers in streets is the access to utilities without a major street removal.

Water trapped between pavers and concrete leads to stability problems and freezing problems. - This applies to both clay and concrete.

For a patio, you do not have to be as correct and can get away with unconventional methods.

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Dick

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Tscarborough

Concrete sand-interlocked pavers are designed as a flexible paving system. Putting concrete or even "stabilized sand" under them destroys the integrity of the engineering. They may or may not fail, but they are not being used for their designed purpose or even in the most economical way.

The same goes for segmental retaining wall units. A concrete leveling slab makes the first course go faster, but it is not part of the engineering (with few exceptions (mainly immersed walls)) and is detrimental to the performance of the wall.

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dirt diggler

no - i had a very good day actually

why is it someone gets bent out of shape when they post a question on a public forum - asking for OPINIONS - and when they get answers that they might not like hearing ... they become defensive



if you were an expert in what you are doing ... you wouldn't have to ask the question "do you guys see any problems with this"


For one - like i said - why pour concrete when you don't have to?? If anything, you're adding more cost to materials. You can set the slope/drainage of the pavers with a stringline.


btw - you should have more than 1" of a stone base for concrete

and a "smooth finish" is a "trowel finish"

but ... what do i know --- you come from a family of masons ....

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Vinny

Tommy, I agree with Dick and Tscarbourough. They arent designed for that way of installation and doing it another way may inevitably have a down side.

But I will also tell you, as a driveway guy, we recieve plans and requests to install pavers in a variety of methods not always per manufacturer specs. One of which recently had a spec to do the install on 2 inches of compacted asphalt glueing the pavers down with a slurry of sand and tack emulsion(a sort of asphaltic glue)

I dont think you stand a chance of destroying the pavers itself the way your cousin does it but when you set a pre engineered product not intended for install on a solid, non yeilding base, if a crack occured in the base slab it would show up on the surface as some sort of fault line.

Pavers are made so they are a foreever surface and now you cant just pull up the pavers, correct the little base defect and reinstall the pavers. Thus you have destroyed the entire purpose for using the pavers to start with.

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Tommy C

"why is it someone gets bent out of shape when they post a question on a public forum - asking for OPINIONS - and when they get answers that they might not like hearing ... they become defensive"

Dirt, I am becoming defensive because YOU were offensive. You implied, in wise-guy fashion no less, that this is MY method of doing it, not my cousins. I was simply telling you that you were wrong. I do my paver jobs the traditional way...however, this method of my cousin's is intriguing to me for a variety of reasons.

I have no problem with the others, who have respectfully offered their opinions and contributed to the forum, while disagreeing. But you came out on the offense, and therein lies the reason why I was "defensive".

A "smooth finish" is a "trowel finish"? Ah, I see that you've read your Home Depot book on concrete finishing, and memorized the correct vocabulary. I think most masons on this board knew what I was talking about when I said "smooth finish".

And Dirt Diggler, I AM an expert in what I'm doing. Please. Again...I do my paver jobs the traditional way...BUT, unlike you, I am open to new methods and ideas.

There you go...am I still sounding *defensive* to you, Dirt Diggler? If so, it is because you are being *offensive*. Consider yourself ignored - I'll continue the discussion with the mature adults who represent the majority of the contributors to this community.

Tommy C

Vinny, Dick, and Tscarborough,

I hear ya - a concrete paver system is designed to be flexible, not a rigid unit.

And I know there's no need to try to reinvent the wheel here, but I've spent many nights in bed thinking of this (maybe that's why I'm always so tired?)

OK, the patio is down. Now it's December. It rains for 3 days and 3 nights straight, the patio is saturated. Water has fully penetrated the 2-3/8" pavers, and is travelling between the pavers and the concrete in the direction of the patio's pitch. The 3rd night, it drops to 28 degrees...that water underneath the pavers freezes.

The pavers are not glued down, except for the borders. On the end of the patio that everything is pitched towards, I've allowed an escape route for the water. If the water underneath the pavers freezes, where are the pavers going to go? They won't become loose, because they are just interlocked, not glued or cemented.

Now Vinny, you posed the question of, what if the slab cracks (which it inevitably will)...won't the crack show up on the surface of the pavers? The answer would be no...don't forget, the slab is reinforced. All those cracks will remain hairline cracks, with no vertical displacement. So the pavers will remain intact.

I know this is not the traditional way that we do pavers, and it seems a bit wacky...but if done in the manner I described, I think it would be good to go.

Tscarborough

It is not that it won't work, it is that you are spending a lot more time and money and not providing any advantage over the standard design.

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