Is a gravel layer necessary under sand for a paver fire pit base?

Question

I'm getting ready to start a DIY fire pit using pavers in a circular design. I've read that the first step (after the obvious digging) is to lay down around 5 inches of gravel or crushed stone. Then, lay down 2-4 inches of sand on top of the gravel. Is the gravel absolutely necessary, and if so, why?

The DIY instructions I'm following also say I should lay the sand, place the pavers, fill in the gaps around the pavers with more sand, wet the sand, allow them the pavers some time to settle, and then remove all the sand between the pavers via powerwasher before filling the gaps with polymeric sand. Why would I want to fill the gaps with regular sand if I'm just going to remove it shortly thereafter?

Thanks for the help!

Answer 1

The gravel is a good idea because reasons. Reason one being that gravel provides much better drainage than sand which will help keep the rather nasty water (rainwater through ashes is the traditional way to make lye) out of the yard or from freezing and heaving in the winter.

The second reason being that gravel compacts better than sand, and can be compacted by beating on it where as sand must be vibrated. A compacted base obviously means less settling down the road.

So while it's not essential it does add a bit of durability for the low price of a couple bags of paver base and thumping on it with a tamper. It's pretty cheap insurance against resetting pavers. But really the biggest recommendation is that you need not be concerned with the drainage and compaction properties of your existing soil.

Answer 2

You fill it with the regular sand so that the pavers remained properly spaced as they settle. Without that sand acting as a buffer you're liable to get pavers that move too much laterally and don't have enough of a gap between them for the polysand to get in.

I'm not sure about the gravel, but I suspect the answer is something along the lines of: Not strictly speaking, no, but it's probably a good idea because reasons.