Laying chipboard floor over screed

[pcb1962]

Planning to cover a screeded floor with 8x2 t+g chipboard sheets. Question is, should I bond the board to the concrete, and if so what with? If I don't bond it I'm a bit worried about having bouncy bits in the middle if the screed isn't perfectly flat, or if the wood expands after laying. On the other hand, if I glue it and the wood tries to expand am I in trouble? I was thinking about just spreading a load of pva on the floor and laying the sheets on that, is that a good or bad idea? Perhaps a more flexible bond would be better allowing the boards a little bit of movement. (The screed was layed last year with dpc and insulation, no likelihood of damp problems). Thanks for any advice.

[kdband]

I think I'd be tempted to screw tile-battens to the floor and then lay the chipboard on top of these rather than directly on top of the concrete. This will raise the level of the floor by another 19 - 25mm depending on the battens you use though. Can't say I'd be comfortable with it just glued.

[Franko]

The last thing I'd think of doing myself is bonding the flooring directly to the screed, especially if you think you may need to lift it at some point in the future. Could you not just lay the thin foam as used under laminate flooring, it would take care of minimal discrepancies in the screed. I would think that as long as you leave expansion gaps around the perimeter, you wouldn't have a problem with expansion. Franko.

[slider]

Why are you wanting to lay boards down?

[PeterCB]

A number of reasons, primarily for load spreading. Between the screed and the slab below is Celotex insulation block. From what I could see when they were laying it, the screed is only a couple of inches thick over the celotex, and I don't feel comfortable with the load bearing ability of that construction were I to put my half-ton lathe and 300kg mill directly onto the floor as it is. So my plan is to lay 22mm moisture resistant t+g chipboard over the screed to spread the load. Also although I could paint the screed with garage floor paint it seems a bit dry and crumbly to use long term without any covering.

[Dave Plowman (News)]

Most new houses that use this idea have polystyrene sheet - perhaps 2" thick or so - between concrete and chipboard. But I'd guess that would raise the floor height too much. Not sure why you want to do this though - chipboard won't add any 'bounce' to the floor.

[The Natural Philosopher]

Lay it fully floating but glued together on a thin polyethylene foam. Leave about 1/4" gap all round at the edges.

As above, I cant see the point meself..

If the screed is insulated, lay laminate, carpet or tiles or real wood straight over the sealed concrete (PVA etc). If its not, construct a framed floor above and fill with insulation..

[PeterCB]

Load spreading - as in my note above the screed is only a couple of inches thick over the celotex block so I'm not happy about putting heavy machinery directly onto the screed, I would be worried about it cracking. I suppose the best thing would be to dig up the screed and the celotex and just put down solid concrete under the machines.

This is my new workshop, I'm not planning on having any other floor covering, moisture resistant high density chipboard will do me nicely. I have non-slip industrial mats in the main areas.

[PeterCB]

The bounce I am worried about would occur if the screed is higher at the edges than the middle, or has hollow spots, or if the boards decide to bow upwards, that's why I was thinking it would be best to bond the boards to the concrete. I guess I'll lay the boards dry and see how it feels.

[Dave Plowman (News)]

Seems it's a workshop? I'd be inclined to level the screed and use a decent vinyl for the surface. Can't really see the point in nasty chipboard.

[The Natural Philosopher]

ah industrial. Hmm. I take it there is no rebar in the screed?

Id have painted the screed meself..jolly good finish is floor paint..

[PeterCB]

Well looking at the pictures again, it seems they did put some wire mesh in, but not exactly what you'd consider reinforcement. There's a couple of pictures here:

don't know how strong that celotex is, but I don't feel comfortable about its ability to support heavy machinery with only a couple of inches of screed over it.

[Matty F]

here:

> I don't know how strong that celotex is, but I don't feel comfortable

Why not just put some thick plywood under the heavy machinery, and paint the rest of the floor.

[The Natural Philosopher]

well you can drive over celotex without compressing it much.

The mesh is where it should be.

How heavy are these things? a couple of tons?

Surely not, in a 'domestic' room.

[PeterCB]

Well if that's the case then I probably have no need to worry, I didn't think to feel how solid the celotext was before they covered it. However, now I have another concern - looking at that mesh, it appears it will have stopped the screed from filling in the gaps between the celotex, so whilst the screed over the celotex will be strong, I have large pockets of air in the floor covered by a bit of mesh and a couple of inches of concrete - or maybe they lifted the mesh and filled the gaps first.

lathe 450kg, mill 300kg

it's semi-domestic, it's accessible from the house, but it's more like an extension to the garage.

[Franko]

Why such large gaps in the celotex ?

[The Natural Philosopher]

Again the mesh SHOULD strengthen the floor to the point where its a sel supporting raft. OK its not pretensioned, but its close.

So about the same as a bath totally full of water..that's really not that massive.

AAh..

[bill]

I have a similar problem and although not identical, my thoughts on the sub ject may generate a solution.

I have a new 25m2 workshop built over a block and beam floor suspended on e ngineering block and brick foundation walls.

The floor I asked for was a poured concrete floor but the builder offered m e a 'just as good' dry screed. The screed is 75mm thick.Needless to say the floor is crumbly and unsatisfactory. I want to bolt wood working machines to the floor to prevent the consequences of an accident should the machines topple over. I tried fixing a 65mm anchor bolt into the floor and lifting it with a crow bar. The screed structure broke away as I suspected.

Short of digging it up and relaying it with concrete I am considering using a thick layer tile adhesive to bond a 22mm t&G chipboard floor to the scre ed. There are tile adhesives that will fill uneven surfaces and bond onto c oncrete floors and chipboard floors. The Chipboard would be glued along the joints to form a large single panel.

I am hoping that with a good bond the adhesion will cause the loading from any fixing bolt to spread in the screed and the screeds face to be supporte d by the chipboard over it.

I have pretty much decided to do this and hope this fixes my problem and mi ght provide some insight into answering the original post.

[Tim Watts]

Did you pay him? And why?

Even screed should be pretty solid once fully cured (a very few weeks) - so not only has he not done what was specified, he's not done it properly either.

[Tim Lamb]

Don't know about crumbly screed but beam and block may have been all the building inspector would accept.

Architects here, (Herts. chalk, clay or gravel) tend to specify B+B knowing the builder will try to convince BC to allow hardcore plus oversite concrete.