How thick need to my concrete garage base be? With usual soil circumstances, 4" (100mm) concrete around 4" (100mm) clear very well compacted hardcore blinded with 2" (50mm) effectively compacted sand or ash really should be sufficient. The perimeter needs to be thickened to your minimum 10" (250mm) by ten" http://sectional-garage-leith37158.mybuzzblog.com/9377073/foundation-details-for-brand-new-concrete-garages