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Gardening with Stone

Flagstone patio on slope ruined by water runnoff.

8 years ago

I'm trying to build this patio on a slight slope. I spent hours using paver base to level the rock, which came in various thicknesses. I had planned to put 0.5"-1" river rock in the gaps between the stones, hoping that water runoff from the yard would not wash out the base. Before I was able to fill the gaps with rock, there was a torrential 2-day rain. Even though I had covered the entire area with tarps, the water still washed out and undermined much of the stone (labor costs down the drain :-( . What can I do to keep the rocks stable and prevent damage from water runoff? Thanks!

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Comments (4)

PRO
KD Landscape
8 years ago
Compaction is the key to a stable, reliable patio base. The photographs do not show how much pitch you have, but normal pitch is 1/8" per linear foot or about 1% for brick and stone patios. It is usually 2% for concrete.

Nothing is foolproof and perhaps you have more pitch than can be detected in the photographs. You could try again and make sure you get the stone in the gaps prior to a rain. When you compact the base rent the biggest compactor you can find/handle. I cannot see what you used for the base but it should be CA-6 which is also known as road mix. You might also consider a granular rock such as decomposed granite for the joints and not river rock. River rock will let a lot of water through and will not help stabilize the flagstone at all.

I hope this helps a bit. Good luck with your project.
User
8 years ago
You need to get rid of the "slight slope" and give the water an alternate route across the patio area. Because although you might be able to pack river pebbles into the crevices between the flagstones, water will erode the underlying packed material every time it rains and water flows from back yard to front.

A drain channel with some sort of diversion on the uphill side to send water through it would work - either a visible rill or channel through the flagstones or a couple of drain tubes under the patio and popping up further downhill could do it.
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I just built a quartzite patio in Reno, NV. I used the new product, polymeric sand and it worked great! I got the sand in 60 lb bags for $20 a bag from Home Depot. My patio is 9X27.5 and I used 5 bags. It looks like regular sand and sweeps into the joints. You then mist it 3-4 times waiting about 10 minutes between each misting. The water activates a weak polymer glue and locks the sand granules in place. We don't have much problems with frost heaves here, but if a stone moves you can pull up the sand in chunks and step on it or use a shovel to get it back to a granular stage, sweep it back in place and re-mist. Although the polymeric sand sets up pretty hard I don't think it would stand up to a leg from a patio chair, etc., so we plan on getting sled style chairs for the patio. It does do well with walking on it and the sand stays put! So far we are very happy with it. I'll let you know how it goes thru the winter. We get very little rain here but we do get snow.
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Ironically, you're not a newbie compared to most people who take on this sort of project. You also fall into the category of people who will probably be most frustrated by having contracters, as you probably have pretty specific expectations about how they should do it. I agree that the site prep is what you sound most leery of, and it isn't rocket science. Get a book on laying patios that explains site prep, levelling, and base material selection (I have one I like called Patios and Walkways, do it now do it fast do it right, by Taunton Press), and you'll see that it's well within your reach. Regarding drainage, think about where the water comes from, and where you want it to go, and slope the patio accordingly. Flagstone has gaps that the water can soak in between too, and you're not exactly in a high rainfall area either, are you? If you want flagstone, you won't be happy with pavers.
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Comments (11)
Jeff, the level is up to you. You can level the area by increasing the amount of mortar or maintain the slope. After you have laid the thin flagstone on the concrete base, and it has dried, you will grout between the stones. Be sure to use some admix (like elmers glue) in your mortar mix so you get a good bond to the old concrete pavement. On the grassy area: You are going to remove the grass down maybe 3" and add crushed stone or granite gravel, lower than the old sidewalk and depending on the thickness of your flagstone. Now tamp it down (again leveled or slopped)and sprinkle some dry portland cement on the top. In this area you want to use a thicker flagstone and you are only going to use enough sand to level the stone. When all the stone is down mist everything so that the portland grabs onto the flagstone and the gravel. Now you are ready to grout between the stones and it will look like one continuous patio. The only place that you will need edging is where the stone is not held in by something e.g. the edge where the steps are. I've actually used the thin edging for pavers that you get at the big box stores. My step comment had to do with the blue line and the lag bolt trim pcs but if you mortar the flagstone you won't need anything special there. Bailey
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To explain my reasons in general…i like a more natural look than hardscaped….A thinnish layer of gravel is easier to walk on and less likely to spread into other areas..skipping the cloth allows a 2” layer to suffice….over time it will eventually mix with the soil for a pretty solid base….after that …I keep a garbage can of pea gravel to fill in occasionally if needed…harder surfaces are more likely to “crack”…discolor..stain…but mostly just does t look “natural” to me……also an occasional spray of water will keep the dust down…as opposed to a harder surface that will require much more water for washing…a small cordless garden blower easily removes leaves and other green bits..so raking doesn’t become a big chore…pea gravel does come in different colors…so call around to see what is available …artistically the material accentuates the creatively shaped sections as well
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PRO
McCumber Fine Gardens
8 years ago
Channel the water to a dry river bed, which will add visual interest, and get it on it's way before the flagstone. Also retain the lower side of the flagstone with stone, use concrete if you need to.
Xtal in Central TX, zone 8b
7 years ago
Don't know, but can a French Drain help to redirect the water?

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