Ply floor - one piece or four?

[cheenyweeny]

My advice is:
If you plan on putting a carpet down then you dont plan on it getting wet so ext ply and lots of f/glass would be ok but on a small orkney os flooring a rib I would expect these to get wet and use marine.
(Bayliner used sheathing ply a while back on bayliners didnt last long - seen it in half cut version in boat show years ago

JOINER !

 

[oldharry]

The differences between marine ply and WPB

Marine ply should have all laminates of equal thickness and the internal veneers should be the same material as the hardwood external veneers.

The voids where internal veneers join should not be greater than a specified width.

WPB is usally glued with the same glue as Marine ply so should not delaminate in wet conditions. But not always!

WPB does not have to comply to any particular standard of construction, and 'coreboard' is quite common, where a single thick sheet of softwood is laminated between two very thin sheets of harder facing veneers, quite often birch, particularly in the thinner grades up to 8mm. Even 12mm may have only 2 internal veneers.

No control over internal voids, which are often large enough to cause a serious weakness in the sheet.

In most cases WPB cores are softwood, which will rot within a short space of time once water reaches them.

I use 'should' rather than 'must' because there are a lot of far eastern 'lookalikes' on the market, often being sold as BS1088 or 'Marine ' grade, which do not meet the standards. A BS1088 stamp means nothing unless it is acompanied by a GENUINE kitemark. Even then 'caveat emptor'!

GOOD quality marine ply is quite difficult to source nowadays. WPB is only suitable for internal non structural work such as furniture or casings. I have used it for internal floors, but it does not last.

 

[ADLS]

Use marine ply seal all edges that have been cut by you. Either lay the floor in section or cut opening panels that are secured down. A length of timeber fitted around all sides below the main flooring sheet will hold the opening piece firm. Paint all faces of the floor and coat the top coat with a nonslip finish, a hand full of sand will surfice for this.