Hi,
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?
Regards,
RichK
How long ago did you get it?
Using old mortar, probably. Try a new bag. If you bought the other bag within the last few weeks, buy your new bag somewhere else.
----- Original Message ----- From: "Doug Miller"
Got it a couple of weeks ago just for this purpose. Did not see any obvious exp date. Did not look to be honest. Had not idea mortar had a short self life.
Would have returnd this bag, but assumed I was doing something wrong.
RichK
How thick are you applying it? It is no good in thin layers.
What consistency is it after you mix it? It should easily stand up...if not, you are using too much water.
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.
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?
Regards,
RichK
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 harden properly.
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.
Thanks Doug,
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 apply it.
Looks like on any time I may have made at least one error, including now expired mortar mix.
Regards,
RichK
You're welcome. Glad I could help.
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.
I wouldn't expect any different. They just claim their "associates" know everything.
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.
_____________________
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.
RichK wrote: ...
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...
--
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.
Dont even waste your time asking them for advice. They're idiots !!!
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 answers.
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 :)
lazarus0
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