[Greenbuilding] Redoing all floors

[Andrew Pace]

Non-acid stains like soy stains or polymer stains only sit on the surface
and in some of the macro-pores of the concrete.  Acid stain works by
chemically reacting with the free lime in the concrete and the salts in the
stain, to physically alter the chemistry of the concrete, thus changing the
color.  The white you see could be a white base stain, or, it could be that
the concrete was never acid etched before using the sealer.  Acid etching
removes the ³cream² off the surface of the concrete.  This is the fine white
or grey powder that will eventually dust off the surface.  Without removing
the cream, any coating or topical stain will eventually peel off the
surface, since its only sticking to dust.

Grinding and shot blasting are two different ways to achieve the same end
result.  It its a large area, shot blasting will be more cost effective and
will require less prep before the next coating is applied.


Andrew Pace
Green Design Center®
Waukesha, WI



On 7/27/11 5:05 PM, "Ktot (g)" <ktottotc at gmail.com> wrote:

> I have been told water-based stain--which was used to get the mottled creative
> pattern that was intended (without white blooms)--does not sink into the
> concrete like acid-stain does. Either way, where the stain and sealer have
> pulled up, there's plain white. It's chalky. Numerous concrete contractors had
> no idea what that was, telling me my contractor must have done a white layer
> of stain first, which I knew was not the case. One finally pointed out it's
> calcium carbonate that chemically reacted to something (the diesel/propane
> fuel? the exterior stain that was used indoors [as I later found out]?) That
> makes sense to me as one gets white on the finger when rubbing those areas.
> The white areas are all white--the stain has completely lifted up. So it does
> not seem to have gone down into the concrete--unless there is more under the
> calcium carbonate.
>  
> Also I should have mentioned earlier much of the sealer seems to have
> disappeared. When put down it was very shiny (as it was supposed to remain)
> but now in many areas there appears to be little or no sealer (this is from
> work done two months ago), and one contractor commented the sealer is soft
> (vs. it supposedly the hardest, most durable there is per my contractor who
> clearly misled me in numerous ways).
>  
> Per the sealer tech rep, the sealer does need to be removed whether I go with
> concrete again or with tile. He seems to lean towards grinding to remove it.
> Is that the same as the shot blast you mention?

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