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Re: 1-3/4" roof slab (w/ 6mm RSB @.10 for S.S. and .20 @L.S.)

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I misunderstood.   I thought the expanded metal you were referring to was the 6 mm bars.
The cement plaster you refer to is what we call 'stucco' here in Florida, and it is always
considered non-structural, and is not considered corrosion protection for the reinforcing,
because of its porosity.

It's likely that the delamination I discussed previously will occur, and then the cover over the
6 mm bars will only be about 3/4".

One last comment -- if the bottom plaster is also based on expanded metal, make sure the metal
is mechanically fastened to the slab in such a way that the fastening will hold up the entire
weight of the 3/4" plaster.  I've seen this type of construction become fully delaminated due to
corrosion of the metal lath, and a 10 FT x 20 FT section of the 3/4" plaster/stucco (about 1,500
pounds) came crashing down.

Regards,

Lew
=======================

Alex C. Nacionales wrote:

> Dear Lew,
>
>   The  1-3/4" slab is reinforced with 6mm @ 4"
> o.c. short span and 8" o.c. long span.
> The 6mm steel is placed at the center of its
> thickness. The bottom slab will  also be
> plastered with 3/4"  1:3 cement plaster mix
> although the structural function of the bottom
> plaster is neglected.  Top and bottom cover is
> 1.5" which is the  minimum allowed except for
> the expanded metal which has only 1/2" cover.
>
> Thank you for your comments and best regards.
>
> Sincerely,
>
> ALEX C. NACIONALES,C.E.
> Iloilo City, Philippines
>
> Lew Midlam wrote:
>
> > In my opinion, you have a 1-3/4 thick
> > UN-reinforced concrete slab, with   1"   of
> > dead load
> > plaster on top of it.  The plaster wil not
> > provide sufficient corrosion protection for
> > the
> > metal, and in a few years it will corrode and
> > expand, resulting in delamination of the
> > plaster
> > from the concrete slab.
> >
> > If this is the case, then the dead load of the
> > plaster + the 30 PSF live load would cause the
> >
> > concrete to be over-stressed.  However, note
> > that UN-reinforced concrete is not permitted
> > for
> > this type of construction (ACI 318-95, para.
> > 22.2.2).
> >
> > My $.02
> >
> > Regards,
> >
> > Lew Midlam
> > ==============================
> >
> > Alex C. Nacionales wrote:
> >
> > > Dear Lew,
> > >
> > > The 1-3/4" slab is one way and supported by
> > > 6"x12" RC beam on fours sides. The slabs and
> >
> > > beams were poured first then the expanded
> > metal
> > > was placed on top of the slab and
> > > and cement plaster 1:3 mix of washed sand
> > and
> > > portland cement type I was applied and
> > cured.
> > > Construction is complete now. I will  send
> > you a
> > > picture if you are interested.
> > >
> > > Sincerely
> > >
> > > ALEX C. NACIONALES, C.E.
> > > Iloilo City, Philippines
> >
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