Preparing timber floorboards for safety flooring

[Restoration man]

Hello
I'm refinishing a small shower room and want to have safety flooring put down. The stuff you get in hospitals. It comes 2m wide and my room is 1.3m wide so it will be able to be laid in one piece.

The floor is original 3 inch wide strip floor boards. I had planned to sheet over with 12mm ply but I won' be able to do this in one sheet.

I'm concerned that the joins in the ply could eventually show as marks on the safety flooring?

A joiner at my work said I should leave a 5mm gap between the plywood sheets and fill flush with silicone?

Only other option I'd considered was hardie backer board?

Any advice much appreciated.

Thanks

 

[dazlight]

Why you using 12mm plywood. Are the wood strips all unlevel you are going over.
On the joints of the plywood use feather finish screed.

 

[Restoration man]

Because I thought it would be a bit hardier and help keep the floor flatter. Also the safety flooring is only about 2mm thick so it will keep the floor closer in level to the carpet of the bedroom.

The existing original flooring is quite good.

Cheers