How do you build a sub-floor over a concrete slab?

[Richard Hollingsworth]

Hi folks. Thanks for reading this.

I have a woodworking shop with a concrete floor that was not pored
level. I have to shim all my WW tools to get them to sit level.

I want to build a wood floor over the concrete slab. Do I just put down
2x4s on edge and shim as needed, then install plywood over this???

Whats the BEST way to install a new floor? (Please don't say rip up the
concrete slab.....)

Thanks,

Richard H.

[Howard Johnson]

Richard Hollingsworth wrote:

> Hi folks. Thanks for reading this.
>
> I have a woodworking shop with a concrete floor that was not pored
> level. I have to shim all my WW tools to get them to sit level.
>
> I want to build a wood floor over the concrete slab. Do I just put down
> 2x4s on edge and shim as needed, then install plywood over this???

Yes, the best way would be to replace the slab, but..

If the slab is in good condition it could be covered by a new layer of
leveled concrete. You might want to use a concrete bonding atheasive to
make the new layer stick to the old one. And/or you might want to
physically secre the layers together. One way would be to use a power
nailer (22 gun) to sink some 2.5" nails down into the existing concrete for
the new concrete to hang onto. Drive the nails thru short 2x4 blocks and
then split the blocks with a screw driver and discard leaving the nails
exposed. Add new matting steel or rebar to the new layer. Be sure to use
earplugs, I about lost my hearing using a power nailer once.

As far as a 2x4 and plywood floor, I would be concerned about a) moisture
seeping up through the porous concrete and rotting the wood and b)
bouncyness or springiness. Even if the concrete floor is dry today, if you
enclose it it may get damp. You should probably lay down a plastic sheet on
the concrete first to seal the moisture. I would also use treated lumber.
If you use shims they could work come loose and you would have a mess. I
would use 2x6s not 2x4s so they could be scribed and fit to the cement below
without getting too flimsy. It will probably be harder than you think to
get the floor to come out flat and level. You might screw the plywood down
rather than nail it to make it easier to fix it someday.

[Ted Ladd]

Hi Richard, I would suggest you use 2x4 sleepers on edge first and level
them.You might have to spend a fair amount of time shimming them to get
them level to one another but the placement of your joists will be a
piece of cake and dead level. Your sleepers would have to be about six
foot on center to accomodate 2x4 floor joists for span capability. You
don't want a floor that is like a spring board. Hope this helps. Ted

[Spike99]

You could look into a gypsum-based product. I found this product
called Level-Right one while investigating radiant heat.

http://www.maxxon.com/

"Level-Right is a self-leveling, cementitious product designed for
thin-capping concrete..."

Don't forget to tell us what solution you choose and how it works out!

On Mon, 7 Feb 2000 20:44:08 GMT, Richard Hollingsworth
<william.ho...@hsv.boeing.com> wrote:

>Hi folks. Thanks for reading this.
>
>I have a woodworking shop with a concrete floor that was not pored
>level. I have to shim all my WW tools to get them to sit level.
>
>I want to build a wood floor over the concrete slab. Do I just put down
>2x4s on edge and shim as needed, then install plywood over this???
>

[dr-...@execpc.com]

I guess I would treat it like a deck. Start with a wall to wall vapor
barrier underneath, then bolt treated wood 2 x 4s to the perimeter walls
using a laser level (rented) to make sure it is level. Divide up the room
into 8 foot widths and level 4x4s to serve as the other end of the "deck",
shimming them up to level. Then use joist hangers or just screw in 2 x 4s
12 inches on center. Now that a level line of wood is established, you can
shim support the wood 2 x 4s from underneath with treated wood, toenail
screwing it so it wont shift. At this point, styro or other insulation can
be dropped into the spaces (depending on code) and then plywood screwed
down. I would screw it down so it can be picked up in case of flood or
????? (maybe you want to run pipes for a bathroom or something).
You can do the whole basement, or just one section at a time. Ingrid

Richard Hollingsworth <william.ho...@hsv.boeing.com> wrote:
>I have a woodworking shop with a concrete floor that was not pored
>level. I have to shim all my WW tools to get them to sit level.
>I want to build a wood floor over the concrete slab. Do I just put down
>2x4s on edge and shim as needed, then install plywood over this???
>
>Whats the BEST way to install a new floor? (Please don't say rip up the
>concrete slab.....)

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