Expansion gaps between plyboard sheets under vinyl

[KeRa]

I am about to buy some 6mm plyboard sheets to put over a mixture of concrete floor and wooden access boards for getting to the plumbing in a groundfloor cloakroom (I was going to lay ceramic tiles but felt it was a bit too permanent in case I ever needed access to the pipes).

The room is only 1.25m x 2.27m but is an L shape and I will need to lay the ply in two pieces to be able to feed it around the radiator pipes. I see in an earlier post that it is suggested to leave an expansion gap between the boards. Surely the vinyl will reveal the joint line with time which somewhat defeats the object of laying it to hide the lines on the floor?

What is the best way to avoid this?

 

[big-all]

i would but it up tight
because ply is a mixture of end grain and cross grain it wont expand more than 1mm
so if you butt it up tight it will only push together without lifting

an expansion gap off 3mm can avoid any probs if its a choice
but for a fully smooth surface best to butt up