[Greenbuilding] Redoing all floors

[RT]

On Wed, 27 Jul 2011 14:29:13 -0400, Ktot (g) <ktottotc at gmail.com> wrote:

> I explained that in my initial email--less than half the required curing  
> time for the concrete. Thus moisture is trapped under the sealer

Actually, one of the reasons that sealers are applied to new concrete is  
to prevent premature loss of the mixing water (evaporation) so that the  
cement in the mix has an opportunity to fully hydrate, thereby bettering  
the chances of a good quality concrete ... so "trapped" is a Good Thing.

The strength vs time curve for concrete pretty much levels off after ~30  
days

   http://www.theconstructioncivil.com/2009/09/concrete-curing.html

so one should try and keep the mixing water from evaporating or being lost  
to the substrate during that "curing" period.

I prefer to simply keep the green concrete tightly covered with a  
protected polyethylene sheet during that curing period but a chemical  
sealer is the more common choice. ("Protection" being cut-off scraps of  
sheet goods like OSB, plywood or even gypsum board)

Too often though, for the sake of finishing expedience, the mixing water  
is allowed to evaporate too rapidly (and/or lost to the substrate , there  
being no moisture barrier used beneath) and then is followed by repeated  
soakings/subsequent evaporations after (improper at that) finishing -- all  
of which lead to poor quality concrete that is weak, dusts/abrades easily,  
much of the cement having been leached out of the mix (ie quite likely the  
whitish "blooms" than Ktot mentions).

And oftentimes, water is added to the concrete mix during placement to  
make placement and leveling easier. That too messes up the all-critical  
water-cement ratio which seriously compromises the concrete quality.


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
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