[Greenbuilding] Redoing all floors

[Alan Abrams]

adding to the comments below--in general--it has become almost an industry
standard to finish concrete incorrectly.  to achieve a strong, weather
resistant surface, the concrete has to be jitterbugged while still plastic.


this is accomplished, immediately after screeding, with a device that is a
flat, lightly framed plate of perforated aluminum, with a looping handle.
The plate is driven with repetitve vertical blows to punch down the coarse
aggregate and bring up the fines.  Hence the term "jitterbug," representing
the motion of the operator's butt as he maneuvers the device.  Then the
surface is lovingly bullfloated until it gleams. all this tends to bring up
a film of water carrying only the finest particles.

Lastly, when the film of water evaporates, the mix is hard troweled, further
compacting the surface.    what is left near the surface is mostly a well
consolidated mix of fines and portland, that (if drying is properly
retarded) will cure to a hard, durable surface.

in contrast, it is universal for the contractor to place, screed, eat lunch,
and maybe sweep with a stiff broom.  The resulting surface is a slurry of
water and portland, barely covering the coarse aggregate.  First frost, this
surface disintegrates, leaving a horrible pock marked surface that continues
to erode.  Almost EVERY sidewalk in DC is placed this way--I cannot take a
walk in my community without seeing yard after yard of this stuff.

AA





On Thu, Jul 28, 2011 at 10:33 AM, RT <Archilogic at yahoo.ca> wrote:

> On Wed, 27 Jul 2011 17:56:11 -0400, Ktot (g) <ktottotc at gmail.com> wrote:
>
>  Talking to various experts, at least 28 days should have been left between
>> pour and cure.
>>
>
> Either you or the "various experts" are confused because the above
> statement makes no sense.
> A look at the strength vs time graph (example shown in link provided in
> previous message)
> will quickly illustrate why.
>
> There is no assurance that grinding down improperly cured concrete
> (whether it be with carborundum stones or diamond stones) will yield a
> better finished surface.
>
> If the concrete was crappy concrete (ie compromised mix quality due to
> addition of water at the site, followed by improper curing) to begin with,
> grinding away the more dense surface layer (created as a result of the
> troweling process) is only going to expose more poor quality concrete.
>
> Then you'd still have to apply surface treatments in order to make the
> concrete look and wear like something other than crappy concrete. And since
> the wear layer would only be a very thin, chemical stew film, it's likely
> need to be refinished again and again and again over the years.
>
> Why bother with the time, trouble, mess , energy and expense ?
>
> I'd cover it over with tile (preferably an unglazed, fully vitrified
> porcelain or such-like) or stone (not a limestone or marble because they're
> too soft).
>
>
> --
> === * ===
> Rob Tom
> Kanata, Ontario, Canada
> < A r c h i L o g i c  at  Y a h o o  dot  C A >
> (manually winnow the chaff from my edress if you hit REPLY)
>
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