Went into the Lab Today!

[The D]

AAAAAHHHHH...but Dave.....

we have noggined out our floors.......then we have installed 18mm ply over floorboards.....at 200mm centres........it is as solid as a rock!!!...
we have allowed a 5mm "expansion" between the 18mm ply boards.....that we have fillled with Silicon.......

its as solid as a rock!.........

why do I need a decoupler?............afterall...they only give a guarentee against laterall movement?........

not diggin............I have to get the car ready........nite nite!

You cant always have an 18mm step at the door and you did not mention if you prime the under side and the edges of the ply you also did not mention weather you acclimatise the ply to the room it is going to be installed in. if you add moisture to the equation I think you may get different results.

 

[Colour Republic]

AAAAAHHHHH...but Dave.....

we have noggined out our floors.......then we have installed 18mm ply over floorboards.....at 200mm centres........it is as solid as a rock!!!...
we have allowed a 5mm "expansion" between the 18mm ply boards.....that we have fillled with Silicon.......

its as solid as a rock!.........

why do I need a decoupler?............afterall...they only give a guarentee against laterall movement?........

not diggin............I have to get the car ready........nite nite!

Oak beams are 'solid as a rock' but that doesn't stop them from getting the shakes and spliting.

40mm oak worktops are solid but if screwed down tight to kitchen units they will twist that kitchen out of shape with the greatest of ease as it expands and contracts.

Now even though ply is engineered to be structurally more stable than a single piece of timber, it still expands and contracts along its grain (lateral movement) You say so yourself and it's the reason you leave a 5 mm expansion gap. You can over fix ply though, so peppering it with fixings won't make it any more stable, in fact it can do more harm because those forces have to go somewhere, normally by twisting the product up (non lateral movement).

Fine do away with ply and use backerboards. The timber or concrete structure they are attached to will still expand and contract.

You won't stop a building from moving no matter how hard you try or what you build it out of. Decouplers are just another way to help combat those forces and allow the building to move without causing physical damage to decorative surfaces. Putting skrim tape over plasterboard joints before plastering or putting decorators caulk between skirting and walls before painting are just the same. It's not a guarantee it won't fail, it's a safeguard.

Whether you think decouplers do the job they claim or that it is just introducing another element open to failure is up to the person who uses them to decide. Maybe by watching the results from your test will help them with that decision, assuming they agree with how the tests were carried out holds water.

 

[Dougs Third Go]

it's fair to say that the only "cracking" I heard was Ray's ciggy lighter:lol:...keep up the good work guys

 

[The D]

at the end of the day (it gets dark)...........and decouplers "shold" be classified as "crack isolators"......because.......that is the one function that they do 100% of the time IMO,if you have any movement in a floor....you need to address it.............(a decoupler wont help!)

and if you have a solid floor.......you dont need a decoupler!!!!!!

weird! EH!

If you use ply that has been stored in humid conditions it may have a large moisture content swelling the ply, if you then fit the ply in a dry room the ply will inevitably shrink as the moisture evaporates from
the ply. Alternatively if the ply was stored in dry conditions and fitted in a humid room the ply will swell as it takes on moisture.
Over the years company’s have come up with flexible grout and flexible adhesive but that has not solved the problem yes it will sick the tile to the ply and it will do a very god job of that but will it stop a fracture appearing in a tile (some even advise you stick the tile directly to the T&G floor boards there adhesive is that flexible ) but the tile is not flexible and people that fit tiles directly to ply are running a high risk of a fracture (I was going to say a failure but it is not an adhesive failure it is the tile its self that will fail)
Uncoupling mats are designed to relieve the stress on the tile caused by this type of movement in the sub floor.

 

[Spud]

had another think about calculating the force applied to the plywood in our experiment and came up with the idea of using a torque wrench to turn the screw thread when we do the experiment , I have been looking on ebay and I can get a digital one or I can buy a conventional one from Halfords

 

[Andy Allen]

how you going to get over the benches breaking...

 

[charlie1]

had another think about calculating the force applied to the plywood in our experiment and came up with the idea of using a torque wrench to turn the screw thread when we do the experiment , I have been looking on ebay and I can get a digital one or I can buy a conventional one from Halfords

Gary, why not just ditch the clamps on the bench and apply the force with heavy weights, wont go in to details ,im sure you could rig something with some rope

 

[Spud]

how you going to get over the benches breaking...

not going to use a work bench ,I went to see Ray today and we did a trial of a couple of ideas we had and the forces involved are far to high for work mate benches,we have managed to get one design jig to seperate the ply wood and transfer a crack through to the tile but it has worked out to be a more complex than we anticipated ,that said once we have the test rig made it will be easy to complete the test and get the results and we are on the right track now

 

[Colour Republic]

I think the biggest obstacle you have is when trying to either push or pull the ply apart that you manage to keep it flat, the few ideas I came up with in my head for jigs the other day would mean the ends would want to buckle up (or down) as you did it

 

[Aston]

rob colour rep makes the valid point..buildings move throughout the year!!

ply is screwed to joists
joists rest on walls
walls are built on foundations
foundations rest on the ground
the ground moves throughout the year..expands in winter and with rain,, contracts in summer

so with that in mind, i'll keep using them when the situation demands...anyway, schluter have only modified/evolved decouplers for timber floors from what the romans first created for laying stone