Laying hardwood flooring over plywood on slab

[m_ouwerkerk]

Hi, I've got a few questions so if anyone could help that would be much appreciated. I'm laying 19mm hardwood flooring on concrete slab. There are tiles fixed to the slab, and I'm lifting them up. They are leaving what looks like a cemet based glue behind (about 4mm thick) - it's hard and level. It's a nightmare to get this stuff off the slab. My plan is as follows:

1) Put down builders plastic over everything (leaving the cement tile glue in place)
2) Use Splitz anchors to fix the plywood onto the slab. As I understand it, I have to lay the boards on a diagonal, with about a 6mm gap between sheets.
3) Secret nail the boards (they are 105mm wide) onto the ply, and also use a decent glue for fixing.

Issues:
1) The ply is only 12mm thick, and I think 15mm is generally recommended. For me to secret nail a 19mm board down onto 12mm ply, the longest nail I can use is 32mm (i.e. that is the length on the 45 degree angle)
2) The boards are 105mm wide - that's possibly a bit wider than recommended for secret nailing.

Questions:

1) Can I get away with using 12mm ply (I have about 50 sheets in the garage so really want to be able to use them)?
2) Does anyone know of a secret nailer that can take 32mm nails?
3) Can I secret nail 105mm boards?
4) What glue product is best to use to fix the boards to the plywood?
5) Do I glue in the groove, and again, what product is best to use?
5) Is there anything else specifically wrong with my above plan?

Many thanks

[Tung tied]

Hi m_ouwerkerk, (http://www.woodworkforums.com/members/m_ouwerkerk/)

15mm board would be better if you can use it, otherwise you could lay the 12mm board on battens or cleats. This will get you the extra height but it may introduce some echo when walking on it.

I've used liquid nails when fixing boards to an existing yellow-tongue chipboard floor. I didn't bother with glue in the T&G slot, just used it under the boards in a sine-wave pattern. A friend of mine just used 15mm cleats between the boards and the slab in his house and it worked ok. It's a bit echoey though.

The boards will move depending upon the weather / humidity. It's good to leave about 3/8" (or 10mm for the youngsters) between the long edge of the boards and the wall. Most expansion occurs across the width.

Secret nailing??? Hmmm gun or by hand?? I'd look real hard for a gun. The nail head is not the only thing that I tend to hit:no:. (It also leaves dents in the boards if you miss. Learned that one the hard way:doh:).

Hope this helps.

Cheers

Bryan

[m_ouwerkerk]

Main thing is I want to be using the 12mm ply, so I want to know if there is a secret nailer around that accepts a 32mm nail that anyone knows of.