Cobblewood/endgrain floor

We are wanting to use our rough sawn red pine 4x4s to make endgrain flooring for our entryway. Its a small space, probably 4’x4’ and concrete right now. Its unheated and gets a lot of moisture from snowy boots in winter.

My thoughts are cutting the 4x4s about 1-1.5” thick and wedging them in side by side with no grout in between, then putting some sort of water proof sealer like Waterlox on top. We have never done this before and I have questions…

I imagine these will expand and contract with moisture and season changes, so should I leave a gap around the perimeter? And if so, how do I keep the blocks tight together with a perimeter gap? Would lining the perimeter with something like cork be a good way to allow expansion?

What do we do between the concrete and wood blocks? Should we seal the concrete first? Or I considered laying a thin piece of treated plywood down and gluing the blocks to that.

Any suggestions are appreciated! This is the look we are going for:
https://aspensonlumber.com/unfinished-flooring/

The show that I watch use a moisture barrier and I feel you are correct about using plywood over the moisture barrier.

That way you have a good level surface and something for the glue to adhere to.

Herringbone pattern is very popular at the present time.

Here is a thread about doing the endgrain floor:

https://permies.com/t/63865/Wood-Block-Conundrum

Can you lay it down in one piece?  If you can, you could build it like a cutting board or countertop and dropped in place.

R Scott wrote:Can you lay it down in one piece?  If you can, you could build it like a cutting board or countertop and dropped in place.

I could if i glued them to a sheet of treated plywood. Whether I put the plywood in first or glue the blocks on first and insert the thing as a whole it seems the end result would be the same. But still not sure how to deal with expansion and contraction of the blocks, how to waterproof and if I need to do anything to the concrete first.