Thread: Flooring over concrete

Hi Schui,
Not an easy job you have decided to tackle;or perhaps should I say your ladyship has convinced you to have a go!
Firstly 12 - 13mm is too thin it will spring under your feet when you walk on it, also you need to place some timber joist on the concrete first otherwise the flooring will follow the ups and downs of this. If it is in a bedroom or study, pretty straight forward, however if it is in a back porch area this is a bit more of a problem.
You need joists possibly 75 x 25 ramset to the concrete every 350 to 450mm apart and your flooring needs to be approx 19mm in thickness to give you a nice sound job. The flooring can be secret nailed through the tongue or possibly glued onto the joists clamping them with a chisel as you go. Do not over tighten otherwise the may expand and buckle, which creates another task. Anyway, have a think about it and also see what some of the other forum members suggest.

Cheers,
Ron.

If the concrete is reasonably smooth then why not just lay a floating timber floor?

Pretty easy as a diy job and there's lots of different wood species available these days.

You can stick your boards down to the concrete with a product from sika.
Dyna bolt a sacraficial piece in the centre of your room and get a 6mm trowel and coat the area with product and then lay about 4-5 boards on top and and then squeeze up using another dynabolted bit and wedges or props of the wall, leave for about 2 hours and the repeat process. Do the other side of thess 4-5 boards by removing the original sacraficial bit and then work bothe ways.
This method is used all the time for exactly that thickness of timber and will work.
Putting Joist on the floor is ok but it raises the floor so much that problems eventuate like the doors and skirting, the list goes on.
I forget the exact name of the product but you get in a sausage form or a tub, not cheap but its the gear.
Scotty

Originally Posted by craigb

If the concrete is reasonably smooth then why not just lay a floating timber floor?

Pretty easy as a diy job and there's lots of different wood species available these days.

The concrete will Always emit moisture from below, this will enter the timber and of course warping will follow. there needs to be an air space between the concrete and the wood. A vapor barrier will help but you need to fasten down the flooring as Rona has suggested by applying sleepers to the flor either by Drill & screw, anchor, ram nailing or Adhesive. then using common stapling practices secure through the toungue at a 45 degree angle and lock the planking to the sleepers. Apply the next tounge & groove etc. You will loose only 3/4" of the room height by adding the sleepers. The extra effort and expense will out weigh the agony of having to re-do the task when the floor fails.

Well I'm no flooring expert but in Australia it's not uncommon to lay a floating timber floor over concrete. They just lay a plastic sheet first to act as a moisture barrier.

Here is a non-biased info sheet on floating timber flooring:

http://www.choice.com.au/viewArticle...+tile+flooring

Read you link a little closer.... It tells you to apply and secure an Underlayment (not just vapor barrier) before installing. That would serve the same as the furring strips. except for the air passage.

Yes of course I read that.

The point is that floating timber floors can be laid over concrete without any of the warping problems that you seem to be concerned about.

Which method is better? I have absolutely no idea. It does seem that your method is a LOT more work though.

AFAIK the underlay is just polysterene sheet layed over the plastic membrane.

Originally Posted by Schui

...And if so, how do you keep the timber tight together if you are glueing only? I dont really want to nail through the timber....

Schui, forget the stuff above about needing to have joists, floating floors etc (sorry people) if you don't want to do any of these. Reading your post it seems obvious that none of these are your plan.

An aquaintance of mine did exactly what you're suggesting and in MHO achieved the best results of any modern wooden floor laid over a concrete base (I should mention I've laid two houses with floating floors over concrete base - you always have a plastic moisture barrier then a thin foam underlayer - these are always sold with the floor. IMHO these sound "flappy" and fake when you walk on them). He used one of quite a few glue products designed to cover the whole surface between the boards and the concrete. This glue layer (it's used with nails I should add) serves both to fasten the boards and provide a moisture barrier and are especially designed for the job. Most wooden flooring shops/suppliers will have a version of this type of product. It results in a beautiful, solid feeling floor. The glues are designed to fill in minor irregularites in the level of the concrete slab.

The nailing technique your looking for (and mentioned by Rona) is often called concealed nailing, and has been used on tongue and groove boards to give a nail free surface for as long as anyone can remember. The nail is hammered at a 45deg angle at the point where the tongue meets the edge of the board and punched so it doesn't protrude (see below). A nail gun set up properly makes this very straight forward.

._________________
............................|__
.Board.................. /__|
.________________/|_______________________
__Glue__________/_________________________
......................../
.Concrete........../ Nail
________________________________________

You need to clamp the boards tightly together until they are nailed. There are specialist strap ratchet clamps made to clamp tongue and groove floors that are probably worth hiring that allow you to maintain the tension (you only have to nail every fourth or so row of boards).

A bit of planning, a lot of patience and time and you'll be laughing.
Have fun!

There are product manufactured just for the purpose of floating floors in the manner you speak but I must have misread the initial post as it seemed to me that you were speaking of using regular flooring as a floating floor.

The special products have interlocking joints that either pull themselves in tight and hold once in place or are made to accept a certain adhesive to bond them. They are manufactured to repel the moisture problems and maintain tight joints. Forgive me if I mis-read and spouted out concerns for you approach.

Seems we were speaking of two different products. as well as approaches.

Schui,
Over west I glued a bamboo floor directly to the slab and this was a common practice in installing these floors with the company I purchased off. I sealed the slab with a slate sealer (think it was that?) and then just used sikaflex to glue the bamboo down. Forgot to mention, the floor was scraped before it was sealed. This is an easy way to go if you are never going to replace the floor, if you have to replace the floor... sell the house because you dont want to be pulling this stuff up

Corbs

thank you all for your advice. 'Toddles' this is for you. your suggestions and advice give me confidence to try this technique. You speak about nailing. Are there nail guns that will drive the nail straight into the concrete? If not what is the easiest way to fix the timber to the slab after gluing?

this thread is good timing as i am in the early negotiation phase with the boss to (not) do exactly the same in a few rooms.

(whats wrong with threadbare carpet ?)

just to throw a spanner in the works, we have slab heating.
(this is vic - the place to be!)

any of you guys aware of constraints with floor covering over heated slabs?

my initial enquiries with retailers have met with that "pity" look as they turn away....

We used to lay 12mm ply with parquetry glue and spikes to the slab first then epoxy glued 9mm-12mm x 50 - 90mm hardwood to the ply. Small brads were used to fix down boards here and there. When floors were finished these fastenings generally were unnoticable.
These floors were pretty solid, suitable for high traffic areas such as a shopping centre, club, airport/office however it wasn't cheap. The end result was excellent and would look great in a home.