What type of plywood is best for strengthening floor

[Milleniumaire]

Hi,

I'm in the process of installing some Omnie TorFloor underfloor heating, having removed all my existing 18mm floorboards, plywood and tiles.

The Omnie boards are 22mm thick and are routed to accept 12mm pipes. It is necessary to glue and screw at least 6mm plywood on top of them to give the boards structural integrity, then follow their specific guidance to prepare for tiling.

I have decided to use 9mm plywood, just to give a little more strength, but when looking for plywood there appears to be a myriad of different types from different suppliers:

Hardwood Q Mark Plywood £27.08 Howarth Timber
Hardwood Faced Plywood £23.81 Howarth Timber
Non Structural Sheathing Plywood £21.66 Howarth Timber
Hardwood Plywood £32.26 Howarth Timber
Structural Sheathing £23.70 Howarth Timber
Marine Plywood £45.32 Howarth Timber
Hardwood Plywood Poplar Core FSC £30.90 Jewson
Brazilian Pine Structural Plywood FSC £16.38 Jewson
Ultipro Hardwood Plywood FSC £34.20 Jewson
Eucalyptus Hardwood Plywood FSC £34.20 Jewson
Hardwood Plywood Poplar Core FSC £30.90 Jewson
Non Structural Hardwood Plywood £23 Wickes

I believe I need to use hardwood ply, but does it matter which? Why so many different types? Is this primarily for different finishes when constructing things e.g. furniture with plywood.

In my case, it just needs to be strong and I don't care what it looks like!

Any pointers would be much appreciated.

 

[JohnD]

the hardwood ply is usually veneered with a paper-thin skin of hardwood, and the rest of it is patched together with layers of scrap softwood, glued together. I had some from B&Q like that, noticed some voids in the ends and dribbled waterproof glue down them, intending to seal them before varnishing the edges to keep damp out.

I dribbled glue down them for days, and it kept draining away into the unseen voids within. I never filled them.

In the past, I had some marine ply used for boatbuilding. At the time there was a quality specification for it, I believe this has now been superceded.

 

[Milleniumaire]

the hardwood ply is usually veneered with a paper-thin skin of hardwood, and the rest of it is patched together with layers of scrap softwood, glued together. I had some from B&Q like that, noticed some voids in the ends and dribbled waterproof glue down them, intending to seal them before varnishing the edges to keep damp out.

I dribbled glue down them for days, and it kept draining away into the unseen voids within. I never filled them.

In the past, I had some marine ply used for boatbuilding. At the time there was a quality specification for it, I believe this has now been superceded.

So, it sounds like you are saying as well as the large range of types of plywood, some is also pretty poor quality!

Based on the price, I would expect marine ply to be the best quality, as well as be waterproof, but I don't need it to be waterproof so don't really want to pay for marine ply.

 

[JohnD]

if you can get into the warehouse, look at the cut edges of the boards, where you can see the inner layers. look out for coarse timber and voids.

the vendors may have a specification that says how it is supposed to be made. It is pretty certain to be from some far-east factory and quality control/regulations compliance may fall short of what we in the EU and nearby countries have come to expect.

most ply is nominally WBP (made with glue that resists boiling water) despite which it will delaminate if you leave it outside and rain gets into the interior through the cut edges.