[Greenbuilding] sealing plywood floor?

Tue Apr 3 12:39:43 CDT 2012

This is one of the succinct summaries of this sandwich:

---------- Forwarded message ----------
From: JOHN SALMEN <terrain at shaw.ca>
Date: Wed, Apr 20, 2011 at 9:18 PM
Subject: Re: [Greenbuilding] building floor on top of rigid foam...
(basement/garage retrofit)
To: ArchiLogic at chaffyahoo.ca, Green Building <
greenbuilding at lists.bioenergylists.org>, satjiwan at alumni.brandeis.edu

 I missed this thread somehow. I can testify that putting a floor directly
on eps foam is a great system. I have done this in a number of renovations,
new homes and a school.  The basic spec. is rigid eps board (minimum 4”)
on a level surface w/ t&g ply sheathing laminated directly to the foam with
a suitable adhesive. That is it.  The level surface does not have to be
concrete – it can be a granular base (sand).

The real point of this approach is to avoid the use of concrete or in the
case of insulating on existing concrete to isolate from moisture and to
minimize the use of unnecessary materials.

As for materials the ‘suitable adhesive’ is generally specified as a
polyurethane foam adhesive (enerbond or equiv.). If the finished floor is
to be ¾” solid wood nailed -  I specify a min. 5/8” t&g ply sheathing. If
it is tile I generally specify either a thickset mortar directly on the
foam (w/reinf.) or an additional layer of ½” ply laminated and fastened @
3” o.c.  I’ve found that most contractors get the concept pretty quickly
but the trick is that in putting down the ply it needs to be flattened and
weighted down while the adhesive sets (concrete block, buckets with sand,
etc...)

For your application I would eliminate any subfloor wood framing
(sleepers). Waste of time and material. eps boards can be ordered cut to
the thickness needed for the finished product. Using foam on an existing
slab it is nice to have additional thickness – 5-6” foam can span any
deflections or defects in the concrete. I would spot adhere the foam to the
concrete.

Essentially the finished floor (eps and ply) is a weight bearing floating
floor that can carry standard interior partition loads well. It is a pretty
nice floor.

On Tue, Apr 3, 2012 at 10:32 AM, Benjamin Pratt
<benjamin.g.pratt at gmail.com>wrote:

> wouldn't 1/2 plywood warp over time? I don't knwo the procedure.
>
> On Tue, Apr 3, 2012 at 12:28 PM, Michael O'Brien <obrien at hevanet.com>
> wrote:
> > Hi, Reuben--
> >
> > To clarify what is being finished--I'm sure it's obvious, but the plywood
> > should be exterior grade. Practically speaking, moisture won't be able to
> > pass through the phenolic adhesive between the plys. Are the two layers
> > free-floating over the sand? Is that OK--they won't move when there's
> > traffic on them?
> >
> > It seems like a hardwood would work better than a softwood like fir,
> > costlier but might hold up to traffic better, especially on half-inch
> > sheets. (I wonder if 5/8" might be worth it for extra stiffness?)
> >
> > I'd suggest coating both sides and all edges with a water-resistant
> finish,
> > while the plywood is dry. Have you looked at Miller's Evolution satin
> > exterior paint? It's reasonably priced for its performance. Miller staff
> can
> > help decide if a wood filler is needed. The satin finish would make it
> > easier to clean.
> >
> > Might be good to leave a little space between edges for expansion and to
> > stagger the joints between the two layers, to slow any moisture from the
> > sand layer.
> >
> > Is that about what you already figured out? :^ )
> >
> > Best,
> >
> > Mike O'Brien
> >
> >
> >
> > On Apr 3, 2012, at 9:32 AM, Reuben Deumling wrote:
> >
> > I'm planning on assembling a floating double layer of 1/2" plywood over
> foam
> > over sand that JOHN SALMEN described here in the past, and as this is
> for a
> > basement wood shop I'm wondering if anyone has suggestions about what to
> > seal or paint the plywood with to maximize its longevity?
> >
> > Thanks.
> >
> > Reuben
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>
>
> --
>
>
> b e n j a m i n p r a t t
>
> professor art+design
> the university of wisconsin stout
>
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