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Question DetailsAsked on 8/22/2013

Does anybody use sand as a base before they pour concrete of a driveway?

I was told by one of the contractor that I needed to put a layer of sand before I poured concrete for the driveway. Another contractor told me that no sand is used because it is the cause for cracks as the concrete moves. I am confused.

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3 Answers


The contrator who said sand causes cracks as the concrete moves is wrong, it doesn't mean the other is right either. Concrete cracks no matter what you do, that is why you see regular spaces groves or lines in sidewalks, its a control joint to allow cracking to occur there rather than where it wants.

Otherwise, what is under a slab depends on the ground you are pouring the slab on, some soils don't need anything, some need a lot of help. From American Concrete Institute ACI360R-10 Guide to Design of Slabs-on-Ground 4.5 Design of Slab-support system 4.5.1 General "After subgrade soils have been classified, the general range of K values can be aproximated from Fig 4.3. Adjustments may be made on the basis of local exprience, expected seasonal changes and expected construction conditions. With this information a decision can be made whether to use the existing subgrade (ground as is), improve it (use a compactor to hammer it down)..., use a subbase and base course (gravel and sand)...".

Long story short, a good contractor will know the local conditions and help with your decision, gravel and sand are used with wet conditions or poor soil types to give drainage, support or just to level the ground for the slab and can be used in other places, common in bigger projects. Do NOT believe a contractor that tells you sand causes cracks or that concrete will not crack in some manner.

Answered 4 years ago by Kelsey


Sand is a proper levelling course for use under pavers and ungrouted brick patios and such. It is definitely NOT a proper base for a driveway - it is too mobile, has low bearing capacity, moves about under load especially if very dry or very wet, and will cause structural cracking of your driveway.

The ACI standard quoted by Kelsey is for building structural slabs - not applicable to driveways. The crack control joints he talks about is for shrinkage cracking control so it occurs in a predetermined and not objectionable location, not for structural bearing failure cracking.

The proper way to build a driveway is to excavate (depending on design load) from 1-3 feet down (generally about 12-18") depending on what your existing soil conditions are, place a structural geotextile if still poor (soft or muddy or clayey) conditions at that depth, then place and compact Subbase material (which may be a crushed rock or a gravel, free-draining, typically 2" minus) up to about 3-4 inches below where the driveway surfacing will be placed, then the top fill layer (the Base) is placed and compacted. This should be a free-draining crushed rock material - commonly 3/4" minus with less than 3% "fines" - material passing #200 sieve, and specified gradation so it compact into a tight, dense layer which will bear load without moving or further compacting. Your local building department probably has code requirements for base and subbase gradation and material types, otherwise the American Asphalt Institute and Amercian Concrete institute have recommended driveway gradation sheets on their websites. Your local streets and state highway department also specify certain subbase and base materials and this is what the local crushing plants will produce to, so if you just specify what your local road department specifies this will be "standard" construction materials.

I would guess the one contractor learned on sidewalks and pavers and never learned how to properly build a driveway, or chose sand because it is cheaper in your area. I would not go with that one.

Answered 4 years ago by LCD


I strongly disagree with statement regarding sand as a sub-base. Contractors have been using it for years due to it expansive qualities. In other words, it does not expand when it freezes. One reason it is used as a backfill or sub-grade material. As with all material, it has to be placed correctly and compacted properly. Sand needs to remain damp as well as other material before placement of the concrete. If you want to build a road, use gravel, but this does not mean you will not have issues. No one can predict the outcome of the harding of concrete. As they say, it will get hard and crack. Don't be afraid of said. It is not used simply because it is cheap.

Source: A retired building official from Michigan.

Answered 1 year ago by petey

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