11-20-2008, 05:10 AM
Depending on what you will be putting on top of the concrete slab the details will vary. The requirements for your particular concrete slab should be spelled out in detail on your building plans. Generally, all loose cinders and or a'a lava should be scraped away since cinder compacts too much. "Blue rock" which is a dense lava is frequently the preferred foundation for under the base course. Generally, it is better to not rip or doze the area you want to put the slab if you can help it. If it is "disturbed" soil, then it has to be compacted back down again. Each slab is slightly different depending on the location of the slab and what is going to be built on top of it.
Kurt Wilson