Flagstone Path - How to Fix Unstable Stones

15 years ago

We just put in a small flagstone path ourselves and the stones are pretty unstable. We did it with little research and no experience, and on a very tight budget so we cut a lot of corners. So we probably did several things wrong.

I think the main problem is that we didn't actually use flagstones. Someone was giving away granite tiles (12x12x3/8") that we liked, so we broke those up and used them as the main stones. I think they're probably just too light. But I'd like to understand what all we did wrong before trying to fix the problem.

The path is on our front yard, about 3 ft wide and 20 ft long, gently curving, and gently downsloped -- there is about a 1 ft decline over the 20 ft distance.

First, we put in benderboards on the sides of the path. We did this without scraping the underlying dirt to be perfectly flat, so the tops of the benderboards aren't even from one side to the other.

Second, we poured in several bags of moist, all-purpose sand. Because the dirt wasn't flat and tops of the benderboards are uneven, the sand depth varies from 3/4 inch to 1.5 inch. We tamped it by pushing down with a piece of wood board -- we did not use a metal tamper.

Third, we laid the granite tile pieces. Their sizes varied, but on average they are about the size of a business-size envelope. Then we filled the spaces between them (which are about 1" width) with 1/4" black beach pebbles.

Right away the stones did not feel solid. They sank and shifted when walked on. After just one day of use, several steps are already out of place. And worse, the pebbles that were between the stones are are all over the place.

So, I think the main problem is that our stones pieces are just too small and thin. But I wonder if not tamping the sand was also a problem? In a normal flagstone path, what keeps each step from shifting under the weight of a person? It seems to me that even if the sand had been packed very tight, it would eventually dry out and become fluid, and would not keep flagstones from shifting under people's weight. How does that really work?

I'd appreciate any input. We'd love to pay a professional to do it, but we just can't afford it. Thanks.

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User
15 years ago
When you are on a tight budget, the worst thing you can do is cut corners and skip the research. Right now - not counting the work you did - you are out the cost of the benderboard, the sand, and the black pebbles, and have wrecked a lot of granite tiles you could have sold or traded for some decent stepping stones.

If you started with granite 12x12 tiles and broke them, they are way too small and thin to ever stay put on a sand base, or any kind of a base. Just the pushing of your feet as you walk will shove them around. Having them on as much as 5 inches of unpacked sand doesn't help at all.

An unmortared stone path is made of 1 1/2 to 2 inch flagstones (any really flat stone will do) that are big enough for an entire large shoe to land on it, or larger - 12x18 or larger, sometimes as much as 3x4 feet. They are laid on firmly packed flat substrate (native hard-pack dirt is what I prefer), and leveled by shoving dirt around and under them until they don't rock. Then the gaps between the slabs can be filled with crushed gravel.

Go back and section by section redo the walkway by puylling out the granite shards and black pebbles, Then rake the sand out of the way and LEVEL the substrate.

For a reasonably budget walkway, set aside a few bucks a week and make a few concrete pavers using readymix and a mold. You can embed the granite shards and black pebbles in the pavers if you want, but you need to have about 2 inches of concrete for weight.

To embed the granite and pebbles, lay then pretty side down in the bottom of the mold and carefully pour the concrete over them, then level the top and let it cure slowly in the shade.

Check the HYPERTUFA forum for advice.

OR: check some of the ratty dumps along the rivers and creeks for busted up sidewalk slabs and recycle them.
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