I am installing a patio near albany Ny. I plan to lay down 6″ of gravel and a couple inches sand then the slate. Should I put down some drainage pipe or foam insulation? thanks
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How well drained is the soil? If it is a wet spot, clay soil, etc then absolutely use foam and or drainage tile. If it is well drained, then frost heave won't likely be an issue.
ditto on what Marson said. No moisture = no frost. Be sure the grade below the gravel layer is sloped appropriately.
Pretty much spot on advice.
Frost heaving requires three elements to occur: conducive soils, water and freezing temps. The first two are typically easier to solve. Conducive soils are things like clays and fine sands that have lower perc. rates and higher capillary action. Clean gravel is not conducive, but well graded gravels can be. Having a clean gravel layer drained to daylight should solve most problems. It depends on frost depth too. We have frost 9-11' deep around here, so the best we can hope for typically is to have something similar to a raft foundation so that the whole thing heaves evenly and doesn't break anything.
Rob
your slab is sitting on top of the frost level, therefore if your ground is very wet, install, otherwise its going to heave and crack no matter what you do.
One of my customers had a brick patio laid a few years ago and it heaves a little unevenly, the bricks separating slightly in a couple of areas. When it thaws in the spring everything settles back to normal. Three winters so far and every spring the patio looks like new, but who's to say that will be the case 20 years down the road. There isn't any real practial way to provide drainage without regrading his entire back yard. In his words, if he has to have the patio re-laid in 20 years, he could live with that.
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On a side note, Ants love patios with a sand bed.