I'm at a loss why the mortar I'm using for patching mostly at this point,
can be practically rubbed off, after setting.
I got a bag of Mason Mix Type S Mortar Mix (Commercial Grade) Quickrete.
Been mixing small amounts for patching other concrete, repointing, etc.
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?
In humid weather the shelf life of an opened bag could be measured in days.
Unopened, it should easily be good for several weeks.
Well, you might be. Old mortar isn't the only thing that can cause that, but
it's the most common. Other causes I'm aware of are:
a) not using enough water
b) using waaaaaaay too much water
c) using sea water or ion-exchange soft water (sodium isn't good for mortar)
d) water being wicked out of the mortar while it's drying (wet down the area
you're patching first - new bricks should be soaked in water)
The consistency should be similar to -- well, to fresh s**t. If it's runny,
you used too much water; if it's dry and stiff, you didn't use enough. The
mortar, I mean.
If you've been mixing it with the amount of water recommended by the
instructions on the bag, try mixing a new batch with about 1/3 *more* water
than the bag says. If that batch hardens properly, then you've solved the
problem; if it doesn't, try a new bag.
Doug Miller (alphageek at milmac dot com)
I may be guilty of several errors. Did not know there was so much to it :-)
Guys I've asked in person, including the youngster at HD, had no idea about
any of this.
Yes, bag has been open for a couple of weeks now. Been applying too thin in
places. Some may have been too thick and some too thin. Using normal tap
water. Working mostly on dry days 50% humidity, but wetting whatever I
Looks like on any time I may have made at least one error, including now
expired mortar mix.
The kid at HD didn't know? Gee, there's a surprise. :-)
That's probably a large part of the problem. Next time, if you won't be using
the entire bag at once, put the rest in a bucket with an airtight lid. An
empty drywall-compound bucket works fine, or you can buy five-gallon buckets
with lids at HD or Lowe's fairly cheap.
If you mean the thickness of the layer, there's no such thing as too thick.
Remember, it cures by a chemical reaction. It doesn't need to be exposed to
air or light. In fact, all other things being equal, the thicker the layer is,
the more likely it is to cure properly.
OTOH, if you mean the consistency of the mortar, yes, too thick equals too
dry, and too dry means won't cure.
As long as your tap water isn't softened, that should be good.
Yeah, well, it's part of the learning process. No real harm done, apparently,
except wasted time.
Doug Miller (alphageek at milmac dot com)
On Tue, 17 Jul 2007 04:56:12 -0500, firstname.lastname@example.org wrote:
Actually, I learned something interesting about the two HDs I use. The
other day I had to stop by before work to check on something, and I
ended up talking to 5 different ignorant idiots who didn't even know
what the store carried (not even sure if they actually knew the name
of the store :>). Normally I go in the evenings, though, and, so far,
I've always been able to find people who actually had intelligent
I finally came to the conclusion that for most of the people who work
there during the daytime this is just a job; most have no special
knowledge, and none of them have any love of customer service.
OTOH, for most of the employees at night, this is their second job.
The majority of the people I speak to are actually working in
construction-related fields during the day, and, at night, they work
at the Depot. These are the people I usually get help from, and I
usually get very helpful answers from them. If you are frequenting a
HD that has no intelligent people, go to a different store.
In my case, there's a store about 3 miles away I normally go to, but,
there's another store about 10 miles away that I only go to when I'm
looking for a particular person. There's this one guy there who can
figure out any problem you toss at him, and the answers are very
practical, and easy to implement; even if you're a novice.
Of course, as with any other place, there are still the young kids who
are there because they aren't qualified to work anywhere else, but I
never ask them any questions, other than, where's the bathroom; etc.,
questions they are qualified to answer :) Just choose your battles, so
to speak :) Never assuime that just because someone is wearing a HD
uniform they're an expert :)
A couple of weeks if it hasn't actually been in the wet but just 50%
humidity unless the bag were left completely wide open I don't think is
long enough to have a major effect just from hygroscopic
absorption/hydration, unless it was really old stock to start with...
I've kept bags partially used for months only closed w/ string or
similar and had no problems w/ it...
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?
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.
So words of wisdom: don't make it to thin (wet) and don't apply it to thin?
Don't apply it too thin, certainly. Pretty hard to make it too wet unless it's
actually runny -- if it's stiff enough to stay where you put it on a vertical
surface, it's not too wet.
Mortar, concrete, and plaster cure by chemical reaction between water and the
Portland cement in the mix, so if you don't use enough water, they won't
That's why the shelf life of opened bags is limited: the stuff will react with
water vapor in the air; when you go to use it, the reaction has already taken
place, and won't happen again.
That's also why you should wet the surrounding area first, and not apply the
mortar too thin: if water wicks out of the mortar into dry brick, or
evaporates into the air from a too-thin layer, there won't be enough water
left in it to react with the cement, and it won't cure.
Doug Miller (alphageek at milmac dot com)
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
There are materials made for patching...I have never used them but
they might be more appropriate.
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.
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.
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.
No one mentioned that some of the premixed mortar (and concrete) are
weak to start with. They dont contain enough of the actual portland
cement or mortar. In fact, I have found that most of them are weak.
Get some raw mortar and add it to the mix, or just get raw mortar and
sand and make your own (cheaper too). You can also add portland
cement and get a very hard mortar, but it will be darker gray.
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