Overboarding T&g

[wayne1]

Hi guys firstly like to say hi as im new to the forum so Hi.
Im in the process of preparing my T&g chipboard floor to take 12mm wbp plywood which i have primed the underside and edges of with a specific product.The area to be tiled is 30sq mts approx.I have replaced damaged chipboard with new(last owners had a rad leak) and the plumber was shy of flooring skills ;-)..I know floating floors of this nature arent ideal but gonna give it a go anyway.The chipboard is good and solid or at least as solid as it can be after repairs.Now my first questions-i plan to leave a 10mm expansion gap round perimeter of room and fill with silicone,should i leave gaps between each board of ply aswel and silicone them also,how bigger gap?.Best adhesive for my situation???.I plan to screw through into joists evry 100 mm and also through into chipboard with spax screws. Thanks in advance guys. wayne

 

[Ian]

Welcome to TF Wayne. I would advise using a cement board over your chip board instead of ply, and 12mm ply is too thin strictly speaking. What tiles are you planning on fixing?

 

[wayne1]

Hi there the tiles are ceramic due to cost implications for such a large area.Ive laid most of the ply already so what are my options,lay some more ply on top of the 12 mm or backerboard maybe?.I dont want to lift the 12 mm as ive put so many screws it looks like a pepperpot lid.Cheers.

 

[Mike Mike]

Hi there the tiles are ceramic due to cost implications for such a large area.Ive laid most of the ply already so what are my options,lay some more ply on top of the 12 mm or backerboard maybe?.I dont want to lift the 12 mm as ive put so many screws it looks like a pepperpot lid.Cheers.

Wayne, As I understand it, the British Standard says that "minimum 15mm Marine or WBP ply" be laid, screwed at maximum 300mm intervals. 15mm doesn't exist, so that means 18mm in effect. BUT, that can be laid directly to joists. So in reality, 12mm ply screwed to T&G and chipboard should be okay (I assume this is your own house, and not a customer's??), as long as there is no deflection in the floor (that is the most important consideration, irrespective of how thick the ply, or any other boarding is).

In terms of adhesive, must be cement based and flexible, I would always advise at least S1, such as Mapei Keraflex Maxi S1. Other brands also exist, so chose whatever is most appropriate for your circumstances.

I assume (given the size of the room) it is not a bathroom, right? If a bathroom, tank the floor. Regarding silicone between the joints in the ply, no, I would not do that, just leave a 1mm gap between them.

Good luck, and you know the old saying, "pics or it didn't happen", which means please upload some photos when you've finished it

 

[Rizzle from the Portizzle]

if your using 12.5mm ply over chipboard this should be 5 ply this means there should be 5 layers glued togerther this must wbp it should be red in couler before fixing soak chipboard in water proof unibond lay ply into when wet scew down every 200mm this lamnate the two sufface together when the glue drys making the floor float as one tiled many floors like this not one has failed .ps can you realy trust britsh standerds if they dont even now what size ply comes in bunch of jokers.real tilers now best been doing the job for years

 

[wayne1]

Hi guys thanks for replys,after reading through a few threads on here i decided to return the sheets of 12mm ply and have purchased at considerable cost the same in 25mm wbp Far eastern ply with a view to ripping up the chipboard and screwing the 25mm straight to joists.I had laid two sheets of twelve mm and no matter how much i tried to convince myself the floor was deflection free it really wasnt.I weighed up the financial and emotional cost of the overboarding failing in a few months time and decided why take the risk?.Can you guys please advise how best to lay the 25mm regards expansion gaps between sheets and round the perimeter at skirtings and also im thinking 60mm screws either Spax or alike.The guy in my LTS is suggesting i go for a two part weber adhesive,anybody any experience with this product?.The room is a 35sq mtr rear extension that will see moderate use.Cheers,Wayne. ps i have also purchased a Weber product PR??? to coat the underside and edges of ply with.