RichK wrote:
"dadiOH" wrote in message

In most cases, even after a few days I can rub off the mortar with
my shoe. It turns to sand. Appears hard to touch with my fingers,
bus seems to have no strength. What am I doing wrong?

How thick are you applying it? It is no good in thin layers.

Some of these were thin, when I was filling some small gaps, and
featherd out tp nothing.

Is there a practical minimum thickness, where it will stay hard?

It simply isn't possible to feather out mortar. The grains of sand in
it have a finite size...the cement is to hold those grains together
and the layer has to be thick enough to do so. How thick? Experiment
and see.

There are materials made for patching...I have never used them but
they might be more appropriate.

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What consistency is it after you mix it? It should easily stand
up...if not, you are using too much water.

Did both and had same results. Was doing it on very dry days, so
thought bit more water would be of benefit - but apparently not.

Excess water weakens concrete/mortar. The usual advice for mortar is
for it to be able to maintain sharp ridges without slumping; however,
when grouting very porous tile I often make it soupy...really runny.
The tile sucks out the excess water almost instantly and the grout
joints (about 1/2" thick) set up rock hard.
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So words of wisdom: don't make it to thin (wet) and don't apply it
to thin?

And experiment a bit.

You can improve the curing by slowing evaporation. You can do that
with a sheet of thin plastic. Misting daily will help too.
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IMO, your biggest problem is that you are expecting too much from the
material; i.e., trying to make it too thin. The strength of
concrete/mortar arises from the aggregate rather than the cement
itself. Doubt it? Mix some cement with water (no aggregate) and plop
out some an inch or so thick; do the same but with aggregate. After a
couple of weeks, compare the relative strengths.

I don't think your problem is from "bad" mortar". I don't do anything
with mortar other than laying 3000+ sq.ft. of Saltillo tile in my
house and I certainly agree that unopened bags of material can harden
by themselves from humidty in the air but in my experience in humid
central Florida it takes weeks/months for that to happen. I have
never had a problem using partial bags 3-4 weeks after opening.

--

dadiOH
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