should I have a sand based foundation with cement mix or a cement solid base foundation for laying slabs onto?

For your sub base 3in scalps then compact with waker plate,for laying paving use 7 to 1 sharp sand and cement wet,never make the mortar mix stronger than the product,for pointing use 4 to 1 building sand and cement ÷ a few cap fulls of pva glue to the semi dry mix,a better bond to the smooth slab.

If your talking about a patio, lay some type 1 mot down, well compacted and lay the slabs on a wet sand/cement mix, about 4/1 use a coarse sand, such as plastering sand, hit down to level with a rubber mallet.

hi, in response to your question about the base for laying slabs onto. i always set my slabs on a wet concrete mix which is a 7:1 ratio of ballast and cement, this is then set on a compacted hardcore base or a membrane. that way i know the paving will not move. however, lots of people do use a sand/cement mix (ideally wet) and this can last! also if you look in the marshall paving book, they recommend mortar dabs, but i have found this method easy to remove when we are replacing patios. please note there are more and more restrictions on new large paving areas as drainage and flooding are very topical at the moment.

if for a patio u should allow 3-4 inches of scalping compacted the i allways lay slabs on a sand and cement mortar. to stop movement, hope this helps