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Discussion in 'Hardscaping' started by CNYScapes, Mar 12, 2006.
Do any of you guys wet down and tamp your stone dust before screeding?
You shouldn't be using stone dust at all. Use washed sand. Something that is better graded than stone dust.
I have always used stone dust because that is what is commonly used in my area. Do you use regular sand? If so, I would guess you keep it covered and dry? And do you tamp that?
Surpisingly, most people in my area do use stone dust as the setting bed. I use yellow mason sand.
Same here in Rochester, CNYScapes, stone dust is what the yards all carry. The tamper I rent drips water as you go, it sets up the crusher real nice, but I'm not tamping the dust-just lay my pipe down on the crusher and screed the dust then lay the pavers. Then do the final tamp to set everything up.
Masons sand is poorly graded and it's particles are rounded (not allowing it to compact well) If you tamp your setting bed, what gives you the interlock you need? You need to set the pavers into the sand via a vibratory plate compactor. This pushes sand up into the joints and in conjunction with your joint sand gives you the interlock that the paving system needs for strength and longevity.
Using stone dust is the old way that masons dry laid stone or slates for walkways and patios. Concrete sand is the best way to gain interlock on concrete pavers. As Chris said, no compacting until after all the pavers are laid, then compacting will force the concrete sand up and into the gaps between the pavers where it will initiate the interlocking process. Using the same sand, or better yet, topping with a polymer sand and compacting again will achieve proper interlock.
Compacted stone dust can also create a nearly impenetrable layer that water will sheet off of rather than percolate through. Stone dust is not recommended as a base material for this same reason. 3/4" minus or whatever you call the base in your region contains larger pieces, up to 3/4" and all the way down to dust. It is easily compacted, makes a sturdy base, but allows water penetration and drainage.
To all of you guys that use stone dust. Take a pinch of it in your fingers. Get it wet and then rub it together. You will see why you should not use to dust. It over time will dissolve. Farmers use stone dust to lime their fields with because it will slowly dissolve. If you read your paver installation guide I am sure it will tell you to use a concrete sand. They don't tell you for no reason. And you say everybody else uses that in your area, well there would be my main selling point. If you want your walkway to last forever like the pavers then you guys should start using concrete sand you will never have a call be for paver sinking again.
Yeah I hear what your saying and I've read the manuals, but you use what is available. And stone dust is what is retailed.
Personally I think that is a piss poor excuse ... they must have washed sand in your area and I bet its cheaper than stone dust/screenings.