I'm planning to remove my old deck, and place concrete slabs 40x40cm instead. A few questions:

  1. Is it sufficient to put a gravel on the ground and sand on top of it? I thought this should prepare a good foundation for slabs.
  2. Should I be placing slabs right to the house foundation (it's standing ~50cm above the ground)? If slabs will be adjacent to the house foundation, will there be a risk of rain water leaking under foundation?

I found this useful video https://www.youtube.com/watch?v=pqsc6zX6SEs

  • I updated question to make it more clear.
    – Mark
    Aug 12, 2016 at 19:08

2 Answers 2


I have seen this done in better and worse ways.

  • using sand as the topper is an invitation for ants to make a new home, stone dust is a better choice
  • what's under the gravel affects how long the job lasts as much as drainage. In colder areas clay soil will heave and push the slabs out of true. Leveling the slabs every spring quickly looses appeal. For slow draining soils or areas where lots of water is expected to drain a base of 6 to 12 inches 5/8" crushed gravel compacted in layers with a compacter topped with an inch to two of stone dust to level is better.
  • at all costs you want to keep water away from your foundation. This is determined by your roof. How far out do the eaves extend and do you have gutters?
  • Without gutters slabs that are slightly tilted away from the house can control water. It does become critical that the slabs continue to slope away from the house or you are worse off than if you had left the surface at grass
  • with gutters my favorite tool of four inch drain pipe with sleeve buried six inches below the surface is an excellent way to channel water from the gutters away from the house
  • thanks for you response. I'm in Canada/Ottawa, pretty cold region in winter. The house has gutters, and eaves extend by 30-35cm.
    – Mark
    Aug 12, 2016 at 19:57

3"-4" of compacted base rock, then an inch of compacted and screened concrete sand on top of that and your good to go. Brush in some polymeric sand in the joints when y9ur done

  • Thank you. Could you give some idea on how to estimate the amount of base rock and concrete sand (in cubic yards) required for the base? BTW, is the concrete sand similar/same to stone dust?
    – Mark
    Sep 2, 2016 at 12:12
  • @Mark to calculate volume take your length and width and multiply by depth in feet and divide by 27 to get cubic yards. Round up to allow for compaction. So a walk (20 ' L x 2 ' W x .3)/27 is about .4 of a cubic yard. Round up to .5. At that size it is easier to get gravel in bags. Less mess that way.
    – kevinskio
    Sep 2, 2016 at 16:10

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