Hard Or Soft Ply?

[Edinaberdeen]

Hi, I am going to take up slightly bowed/loose bathroom floorboards up to replace with plywood. Then put marmox, ufh, slc and ditra on it before 6sqm of travertine.
The floorboards are 22mm but I am struggling to find 22mm ply up here only far easten 18 or 25 mm.

Would 18mm hardwood ply be better than normal softwood ply, its £55 instead of £30.
Thanks

 

[Dan]

You want WPB ply, weather and boil proof, exterior grade. IMO. The best of the ply.

 

[J Sid]

And seal the underside and edges before you lay it to waterproof it.
I would be happy with 18mm on that size floor if extra noggins are put in.

 

[Dan]

Sounds like it'll be a nice job when it's done. Don't forget the pictures!

 

[Edinaberdeen]

Hi, thanks. It will be WBP, sealed and screwed with noggins every 40cm.
Will probably get hardwood, and get some pictures when the demolition is done.

 

[Russell brown]

Far eastern ply is better than wbp in my opinion.

 

[Rizzle from the Portizzle]

here you are going the wrong way take up floor boards solid block were ply joints meet ie joins of ply 4x2 will do now fix 12mm far eastern ply screw down now soak with wood glue then cross ply with 12mm ply across other joints screw down when glue drys and pulls sheets tougher it will have four times the streght of 18mm or 25mm ply now use ditra heat or thermo net this will reduce the highet by at least 6mm take out the marmox boards plus the adhesive 8mm less so you have reduced the highte by 14mm

 

[Edinaberdeen]

Hi, excuse my ignorance but why will 2 sheets of 12mm glued ply be stronger than a 25mm sheet of ply presumably glued under compression in a factory?

 

[J Sid]

If you stagger the joints it will become stiffer and Thu improve the strength of your floor

 

[Edinaberdeen]

That makes sense, thanks.
Would the same apply to Qmark construction rated WBP 9 mm ply in glued in 2 staggered layers being stronger than 18/22 mm ply?

 

[J Sid]

I'm not a structural engineer, but I don't see why not

 

[Rizzle from the Portizzle]

That makes sense, thanks.
Would the same apply to Qmark construction rated WBP 9 mm ply in glued in 2 staggered layers being stronger than 18/22 mm ply?

i would only use far eastern 12.5mm for joist build up

9 mm wbp can be made with soft white ply and only 3 ply deep so two layers only 6 ply to flimseys

12.5mm good quality far eastern ply is 5 ply 65% stronger two layers 10 ply deep hard as nails