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Old 04-23-2009, 08:55 AM   #1
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Flagstone patio - concrete slab or no?


I'm going to install a flagstone patio. My question: is there any way to avoid having to pour a slab?
I'm in central Texas, where there's not a lot of rain; half of the patio will be covered, though not enclosed; there is no slope to my backyard; my existing house slab foundation is in good shape with normal cracks I think (1992 construction); soil is a bit clay-ey; and this part of the city is not subject to foundation issues.
I've heard of laying flagstone into a sand/dry cement mixture, then wetting the entire area so the cement hardens. I believe the cure time for such an approach is a week or so.
Any thoughts? I plan to be in this house for a long time.

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Old 04-23-2009, 12:42 PM   #2
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Flagstone patio - concrete slab or no?


You can deffinately set a flagstone patio on a good crushed gravel base. As a conctractor in a freeze/thaw climate, I will only do them on concrete, mostly because I feel there's less maintenance, weeds, shifting, ants, etc. Also because I'm a mason, not a landscaper, & I like the looks of grouted joints better. As a HO though, it's easier & more forgiving to dry-set the stone in gravel IMO. Start with digging down to a solid, uniform soil, add 4-8 inches of limestone gravel (if local), compact the gravel several times, water hard gravel well, allow for 1-2 inches of fine limestone screenings for fine tuning stones (depends on thickness variation between the flag your using), set stone with min. 1/4" pitch per foot. Leave a semi-uniform gap (1/2" min., 1.5" max. IMO) and fill with sand, dirt, screenings, Polymeric sand, etc. My vote would go towards the larger grit Poly sand for this, as rain can wash the others out faster, but it all depends on the look your going for.

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Old 04-23-2009, 01:05 PM   #3
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Flagstone patio - concrete slab or no?


Quote:
Originally Posted by txpatioslab View Post
.....I've heard of laying flagstone into a sand/dry cement mixture, then wetting the entire area so the cement hardens......
Any thoughts? I plan to be in this house for a long time.
If you get ten replies that say that is the best technique under the Sun, I for one would not attempt it unless I could see for myself the ten examples after ten years.

You don't want to get stuck with flagstones in a cementious base that will be expensive to redo because of unforeseen problems.

I'd take the advice from jo
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Old 04-23-2009, 01:42 PM   #4
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Flagstone patio - concrete slab or no?


Also because I'm a mason, not a landscaper, & I like the looks of grouted joints better. ... My vote would go towards the larger grit Poly sand for this, as rain can wash the others out faster, but it all depends on the look your going for.[/quote]

I too like the look of grouted/mortared joints. If I want to mortar the joints, do you think I definitely need a slab? I would like a very flat, seamless surface. The Poly sand will wash out over time, like any non-mortared filler, right?

Thanks for the responses. Very helpful.
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Old 04-23-2009, 07:39 PM   #5
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Flagstone patio - concrete slab or no?


I have a small area of flagstone set on gravel with mortared joints at my dogs kennel (yes she's spoiled!). It is set directly above/against a 2-3 foot retaining wall, so the area has settled an inch or so. The mortar/ portland has a few cracks, but is still staying together well, & it's 5 years old. On a good hard gravel base in a mid climate, I think mortared joints would do fine, as long as you can live with a few possible minor hairline cracks. Maybe TS can comment on this also, as he is from your region & I'm sure he's dry-set plenty of flag.
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Old 04-14-2010, 11:41 AM   #6
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Flagstone patio - concrete slab or no?


We currently have an old concrete slab 9x6 patio. It's already broken and part of it is a bit sunken. We live in Western WA, so we get plenty of rain, not overly hot and not super cold weather.
Have you ever heard of anyone breaking up slab into various sizes and staining it to make it look like flagstone then re-laying it to create a flagstone look? We're going to try that this month, do you have any pointers? (We don't want to send old slab to wasteland).
Our plan:
*clean slab, break up in various sizes, set it aside to stain (with semi-transparent stain), level & tamp the area, will be using garden wall block to "frame in the patio".
*Lay garden fabric to resisit weeds.
*Set garden block on parameter to frame in patio.
*Back fill the area with 3/8-crushed gravel, level & tamp.
*Add sand, level, screed, and tamp.
*Lay stained pcs randomly like flagstone.
*Fill cracks with sand.
I may even submit "before", "during" & "after" pics, wish us luck!


Last edited by bonbon; 04-14-2010 at 11:50 AM.
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