# Forum Home Renovation Flooring  Attaching ply to a concrete slab and laying floorboards

## The Dec

Hi Guys 
I have had a concrete slab poured for a new extension which adjoins an existing one. 
The concretors have caused me a slight problem in that the new concrete slab which was poured and is not the same height as the original. (ie; the new section is approx 9mm higher). 
Through this entire area (ie; the old and the new slab) I was thinking about secret naling 133mm * 19mm Tasmanian Oak flooring to 19mm ply. 
Given that I now have the problem of the different heights bewteen the old and the new slab.  
I was thinking off secret nailing one section to 19mm ply and then secret nailing the other section to a 10mm ply so that the floor is all even. 
Can anyone give me some advice if there is be a better option available to me (ie; should I just glue the floorboards to the ply rather than secret nail them) 
As I have read somewhere that its not ideal to secret nail wider floorboards and I am also concerned given the different heights in ply that I am going to have to use. 
Thanks 
The Dec

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## shauck

I wonder if you could use a levelling compound to get the floors to the same height?

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## Levey

I think from memory that AUS standards require 2 fixings (nails etc.) per floorboard when you exceed a cover width of 85mm? Please correct me if I am wrong  :Smilie: 
Having said that, If all of the boards are glued to the plywood subfloor it becomes more of a Direct-Stick senario, hence no AUS standards and has been done for many years, get as much advise as possable before you proceed.

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## ringtail

I'd go 9 mm ply on the old floor then the standard 16 mm ply over the lot. I think ( from memory) levey is correct re board width and secret nailing although with bostik ultraset, t&g and end matching things may have changed - consult floor supplier or go with the standard width board.

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## Larry McCully

Hi Dec, In your case the best solution is to fix down on the new area 9mm ply, then if you want to then fix over the whole of both areas 15 mm or 19mm ply. That would be the procedure that a contractor would do on a comercial or residentual building site. Make sure that you lay down a layer of black builders plastic first under the ply. This acts as a vapor barrier so no moisture from the concrete will enter the ply substrate.
Fixing the ply would be using Macism splitz concrete anchor suitable for ply thickness, dont use nylon plugs or simular.See attachment splitz_tech.pdf. 
laying procedure: Install plastic, lay down ply (9mm) drill through ply and into the concrete using a masonary bit on a hammer drill, insert pin, hammer down. Heads need to be flush with top surface or even a mm or 2 below the top surface. Use 20 pins per sheet. 50mm from the edge, then 4 across the sheet x 5 rows down the sheet at even spacings. 3mm gap between each sheet. You dont want them rubbing against each other, they squeek a little bit latter as they expand with the seasons. Have fun.

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## shauck

Larry, do you stagger the sheets?

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## Larry McCully

Yes, it is always best practice to stagger the boards, there is a good reason for it, it keeps any continual lengths of gaps away from any floor board edges. you should also lay the boards so that they are running lenght ways down the direction of the timber floor to be laid. What i mean is that if you flooring is running east to west, the ply should run north to south. This keeps the 1200 width running along the flooring edge. Does thAt make sence, i hope i explaned it logicilly enough with out to much confussion.

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## Dusty

Larry McCully??? I once knew a guy around these parts with such a name. Would you be that guy??

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## shauck

Thanks Larry. I'm not actually doing a floor like this but you never know when you might come across such a job.

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## Larry McCully

Hi Big brother, yeah its me, so good to hear your voice. I thought it was time that i fronted again. I been of the tools and in the office for the past coupla years. Still in flooring thou, as a senior estimator and tech wizard for a flooring company. That folded about 3 months ago ,so i thought i would kick into gear again. its so good to be back here amoungst friends. I had a bit orf a crash a couple of years ago and i  had to sit back and let it flow past. But as they say,you cant keep a good man down. I am looking forward in consulting alongside of you again. Il have to catch up with Gazza and the other lads. is trev still about. talk soon bro............

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## Gaza

> Hi Big brother, yeah its me, so good to hear your voice. I thought it was time that i fronted again. I been of the tools and in the office for the past coupla years. Still in flooring thou, as a senior estimator and tech wizard for a flooring company. That folded about 3 months ago ,so i thought i would kick into gear again. its so good to be back here amoungst friends. I had a bit orf a crash a couple of years ago and i  had to sit back and let it flow past. But as they say,you cant keep a good man down. I am looking forward in consulting alongside of you again. Il have to catch up with Gazza and the other lads. is trev still about. talk soon bro............

  i thought you were working for charles?

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## Larry McCully

Hey dude, that i was. But he is trying to sell randwick store, so i had to go. He is concentrating on Uniwood a lot more , and is spending big time on more product, so i was a expence he didnt need.

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## Gaza

> Hey dude, that i was. But he is trying to sell randwick store, so i had to go. He is concentrating on Uniwood a lot more , and is spending big time on more product, so i was a expence he didnt need.

  gota, no good for you. there is alot of copy cat uniwood around now with big savings, so its going to take him more work to push his stuff, he was bring in bamboo i herd. 
you back on tools or looking for another job in office?

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## Larry McCully

Which ever comes in first, I have been applying, nearly ended up with Mike from Absolute, i am thinkin about getting back on the tools. I got a couple of small ones to do. I agrree with you on the Uniwood, its comming in from everywhere.

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## Smithers

> Yes, it is always best practice to stagger the boards, there is a good reason for it, it keeps any continual lengths of gaps away from any floor board edges. you should also lay the boards so that they are running lenght ways down the direction of the timber floor to be laid. What i mean is that if you flooring is running east to west, the ply should run north to south. This keeps the 1200 width running along the flooring edge. Does thAt make sence, i hope i explaned it logicilly enough with out to much confussion.

  
Why bother sheeting the whole floor with ply? Seems like a huge waste of material and money to me.  The way I do it is to rip 50mm strips of ply and and lay them in runs about 350mm apart. (Sort of creating very thin joists.) Then fix boards to that.  A fraction of the time and cost and does a perfectly good job.

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## Larry McCully

Yes i agree to a point. I have used 15mm thick ply, but i keep the width to at least 80mm. wider battens stabilize the flooring better. less chance of squeeking. Even thou the joist systems are 45 - 50 wide, i prefer wider battens to get a more stable installation.
Any battens that dont need packing is fine using 15mm, but the min thickness ply needed to be used if you are going to pack them is 19mm. and pack at 350-400 centers.
In the old days, we would call a floor fitted on battens a " Acoustic floor" for the reasons being that floors fitted on battens produced a hollow sound, where as a ply fitted floor was more solid under foot and had no hollow sound. We used to give our clients the option if they wanted a authentic sounding floor or a quiet floor.

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## shauck

Can I ask, what is the best/easiest method to determine how you pack the concrete floor, it's highs and lows and what level of accuracy is acceptable or best practice?

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## Larry McCully

The best level and the most widly reconised even with the specifacations and the code is 3mm in 3mt. That means that the fall or rise needs not to exceed a fall or rise of 3mm over a 3mt distance. The best way and the quickest way i find is with a 3mt long straight edge and place it on the floor. When you identify the hollows or rises, then either grind back small rises or use a leveling compond to fill the hollows. There are different methods for identifying the depth and the area of the hollow. I just mark out on the floor the contact points where the concrete meets the straight edge and i write on the floor the depth of the hollow. That is where i pour the compound. Any good project starts from the foundation. If you have a good flat and sound foundation, then it is going to make your work a lot easer.Level foundations are important at the sanding stage

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## shauck

Cheers Larry. So pretty much like straightening a stud wall. I wondered if over the greater distance a dumpy or laser level was also used just to get the difference betwen highest/lowest points as well, just in case whoever laid the concrete didn't do a great job of it. I guess if it rains on it you'll see what's going on a bit too.   :Biggrin:  Although, If you are coming in at the end to do the floor, a roof is on.

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## perf

Hi Larry, excellent advice. Do you use the mushroom head and drive flush or just below? The strip method detailed further on, in your experience, which produces the better result?

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## Larry McCully

The countersunk head is the go. And drive it home flush or a extra tap to sink it down a bit below. Cant have heads that stick above the batten, causes the floor to not sit tight. 
Both systems are good, I think it depends on the individual. Some like it noisy, some like it quiet. I like both.

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## Larry McCully

Never used a lazer to find the hollows,much quicker with the straight edge and a piece of chaulk  

> Cheers Larry. So pretty much like straightening a stud wall. I wondered if over the greater distance a dumpy or laser level was also used just to get the difference betwen highest/lowest points as well, just in case whoever laid the concrete didn't do a great job of it. I guess if it rains on it you'll see what's going on a bit too.  Although, If you are coming in at the end to do the floor, a roof is on.

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## Gaza

> Never used a lazer to find the hollows,much quicker with the straight edge and a piece of chaulk

  We use laser to pack battens and work out heights for adit across large areas small areas 4mt length of alu does the job, when we pour topping we put in guide nails using laser if we are trying to make floor slope or meet a set height

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## shauck

Nice. Thanks Larry, Gazza.

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## Larry McCully

> We use laser to pack battens and work out heights for adit across large areas small areas 4mt length of alu does the job, when we pour topping we put in guide nails using laser if we are trying to make floor slope or meet a set height

  Same here, lazer is the only tool for batten levels and in some cases if you have to do flood topping using ardit Z8 or K15. But for small hollows, i am going for the straight edge. It enables me to define the outer edge of the hollow much quicker. Wher the straightedge meets the concret at the point of the hollow starting, i mark it with a x then i move down 300mm and mark again at the meet point. As you progress down the floor, a clear patten forms and then you just join the dots to see the outline of the hollow. I mark depth references as well in the hollow. I gauge the distance from the underside of the straightedge to the surface of the concrete and mark that reference on the concrete. It allows me to see the variations of depths and then i can calculate the amount of compound to use.

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