I checked with th Direct Lift distributor, they recommend 4" slab but the guy said that with the 4 pads, the weight is distributed well and that 4" is an over estimate to be on the safe side. As far as it tipping over, they say that if it ever tips over, the fallen lift will be the least of your worries as the earthquake will have damaged your house much worse. There are provisions to bolt it down but for me that would defeat the purpose of buying this lift. Its amazing how easy it is to move with the caster wheels.
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