# Just Portland cement as a mortar?



## Waterbug

I had a person telling me that using just Portland cement and water would make a good, waterproof, mortar for laying stone. He kept referring to it as "Portland cement powder" which is not a way I've ever heard of Portland referred too. He also said Portland and water could be used to create a "paint" which could be brushed onto concrete to make it waterproof. Not a lot of details beyond that were given which makes me suspect he really doesn't know what he's saying. He said he worked with, and learned this from his grandfather who was a professional brick layer. So, I don't know, maybe this is just something I never heard of. He also used "cement" and "mortar" interchangeably which to my ear sounded like he didn't understand much.

I build water features and am not a trained mason, so maybe I'm missing something. I tried searching this site and Google, but I don't have any good search terms. "straight Portland mortar", etc. I was taught you would never use just Portland and water for anything, too brittle.

My question is am I missing something? Has anyone heard of such a mortar or waterproofing? If true I would like to learn the specifics but need a term I can search. Thanks.


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## stuart45

Waterbug said:


> My question is am I missing something? Has anyone heard of such a mortar or waterproofing? If true I would like to learn the specifics but need a term I can search. Thanks.


Try googling cement grout.


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## dom-mas

You can't lay stone with a portland slurry. It can be used as a grout as Stuart suggests.


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## 2low4nh

It can be used. I have done it. I would refer to it as a slurry mix. it works great but I should say this is for stone masons that are really good with dry laid stone work. You must know what you are doing with dry stone before using this. We have used it on several fireplaces where a dry laid look is desired but a mudded stone is needed. the slurry is back buttered on the stone and used to lay it up and then the wall gets grouted with a regular stone mud mix to fill any voids. it works great. I am not sure about using it as a waterproofer though. It might work but don't think it would last that long.


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## Waterbug

Thanks. Most of the sites I found seemed to say there were other ingredients in cement grout. Civil Engineering Portal did say just cement powder and water is a grout.

That made me wonder...I use anchor cement sometimes but always assumed there were other ingredients, and there probably are. Would just Portland and water work well as an anchor cement? That would save me some $$$ and trips to the store.


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## dom-mas

yes, portland and water are good as anchor grouts. And portland slurry cannot be used as a mortar because mortar contains sand (or some kind of aggregate) by definition. If you are using Portland slurry as a "glue" to hold dry stone together then yes, but not a mortar and if there is ANY movement in the wall it will crack and fail.


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## Tscarborough

Portland cement and aggregate alone is normally too hard and is very susceptible to cracking. Portland cement and water is a slurry not a mortar and is unsuitable for use as mortar (and is a damn poor slurry for anything other than a bond coat). Portland cement slurries or mortars are not waterproof without specific additions.

To build a stone water feature that will have water running over it or that is supposed to hold water, the waterproofing is located UNDER the stone and mortar and is usually a flexible membrane type waterproofer or pool plaster.


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## Waterbug

I never heard of using portland slurry for bonding, so thanks for that. And portland slurry was another search term for me.

And that's good news on using it as an anchor cement.


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## JBM

Ya ive used it for the backs of bluestone or granite.


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## brokensword

*cement aquarium*

Just to set the record straight, I'm the one that is relaying using cement as a 'slurry' for waterproofing. The OP is in error with a lot of what he's relaying here. 

I said one could (and has; my father built 4 cement aquariums ((not concrete; cement, as in Huron/St. Mary's 'powder' mixed with the appropriate sand and water)) and used the 'powder' mixed with water, to waterproof the insides. No other ingredients, just mixed a paste that would not sag nor run down the sides.

I think I know enough about bricklaying/masonry to realize the OP has not been paying attention. My father worked as a bricklayer for over 40 years, and I've bricked two homes, built one fireplace, laid cement-paver walks, laid conc slabs, and all are still around without having any repair to them, and this is over 27 years ago.

Anyway, I didn't like the way the OP presented the problem/solution and wished to get it straight. 

btw, I HAVE seen/torn down structures which HAVE used cement as the mortar/bond material. They WERE a b*tch to clean and salvage. Too, cement is used as the bond for the pavers as well as the firebrick in the fireplace. So, it isn't fair to say that cement is NOT used as mortar (bonding) material.


Carry on, WB; I applaud you at least trying to educate yourself. When you get your own cement aquarium built, come see me. 


Michael


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## Tscarborough

Portland cement is not waterproof alone, no matter how long it has been done. It is MORE waterproof than limestone for example, but it is not waterproof as a slurry or a mortar (unless the mortar contains waterproofing aggregates like marble dust).

Portland cement and water as a slurry is a bond coat, not a mortar. A slurry is at most 1/8", but generally less than that. Slurry used to set firebrick is also 1/8" or less, but portland is a poor use for that as well. Plain old fireclay ("a mineral aggregate composed of hydrous silicates of aluminium (Al2O3.2SiO2.2H2O) with or without free silica.") works better.

The reaction that creates the binder that makes portland cement work begins to reverse itself at 500 degrees, and that is a non-reversible reaction.

Portland cement is used as a mortar and for many other things but not alone with water for anything other than a slurry for a bond coat. The aggregate size and load has to be designed to work with the joint size.


One more time:

Portland cement and water is not suitable for anything but a bonding slurry. Even a rubbing mix has to have aggregate.


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## brokensword

*heh*

guess the aquariums in the basement of my old home are mirages, then. They were just as I described, and never leaked. There were no additional additives. He did paint the outside white, just to make it look nicer, though. You think all that oil based paint is keeping the water inside a 4' x 2' x 3' (approx) cement box? And what about the side attached to the blocks, which backed up to the laundry room? Nary a drop of water. Now, maybe he put in some magic marble dust into the mix? Nah, watched him do it and twas just the powder mixed with water.

Never said my father used 'slurry' to set firebrick, I said they were laid with cement. You know, the Huron brand variety, mixed with sharp sand.


Ah well, there goes 40+ years worth of experience!





Tscarborough said:


> Portland cement is not waterproof alone, no matter how long it has been done. It is MORE waterproof than limestone for example, but it is not waterproof as a slurry or a mortar (unless the mortar contains waterproofing aggregates like marble dust).
> 
> Portland cement and water as a slurry is a bond coat, not a mortar. A slurry is at most 1/8", but generally less than that. Slurry used to set firebrick is also 1/8" or less, but portland is a poor use for that as well. Plain old fireclay ("a mineral aggregate composed of hydrous silicates of aluminium (Al2O3.2SiO2.2H2O) with or without free silica.") works better.
> 
> The reaction that creates the binder that makes portland cement work begins to reverse itself at 500 degrees, and that is a non-reversible reaction.
> 
> Portland cement is used as a mortar and for many other things but not alone with water for anything other than a slurry for a bond coat. The aggregate size and load has to be designed to work with the joint size.
> 
> 
> One more time:
> 
> Portland cement and water is not suitable for anything but a bonding slurry. Even a rubbing mix has to have aggregate.


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## Waterbug

JBM said:


> Ya ive used it for the backs of bluestone or granite.


Is there an upside to not using sand? You still mix it thick like a mortar, or like a slurry?

And I assume the stone was laid on a horizontal surface. From what I've now read about slurry for bonding it would always be on a horizontal surface? Too loose for vertical?


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## Waterbug

Tscarborough said:


> Portland cement is not waterproof alone, no matter how long it has been done.


That fits what I was taught.



Tscarborough said:


> The reaction that creates the binder that makes portland cement work begins to reverse itself at 500 degrees, and that is a non-reversible reaction.


Fire brick mortar was really expensive...glad it was worth the cost.

BTW, I apology for inviting rudeness. I have learned a couple of things here and it's appreciated.


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## JBM

Waterbug said:


> Is there an upside to not using sand? You still mix it thick like a mortar, or like a slurry?
> 
> And I assume the stone was laid on a horizontal surface. From what I've now read about slurry for bonding it would always be on a horizontal surface? Too loose for vertical?


I dont lay much bluestone in an upright position.


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## Rockmonster

brokensword said:


> Just to set the record straight, I'm the one that is relaying using cement as a 'slurry' for waterproofing. The OP is in error with a lot of what he's relaying here.
> 
> I said one could (and has; my father built 4 cement aquariums ((not concrete; cement, as in Huron/St. Mary's 'powder' mixed with the appropriate sand and water)) and used the 'powder' mixed with water, to waterproof the insides. No other ingredients, just mixed a paste that would not sag nor run down the sides.
> 
> I think I know enough about bricklaying/masonry to realize the OP has not been paying attention. My father worked as a bricklayer for over 40 years, and I've bricked two homes, built one fireplace, laid cement-paver walks, laid conc slabs, and all are still around without having any repair to them, and this is over 27 years ago.
> 
> Anyway, I didn't like the way the OP presented the problem/solution and wished to get it straight.
> 
> btw, I HAVE seen/torn down structures which HAVE used cement as the mortar/bond material. They WERE a b*tch to clean and salvage. Too, cement is used as the bond for the pavers as well as the firebrick in the fireplace. So, it isn't fair to say that cement is NOT used as mortar (bonding) material.
> 
> 
> Carry on, WB; I applaud you at least trying to educate yourself. When you get your own cement aquarium built, come see me.
> 
> 
> Michael


You seem to be more argumentative than you have to be.......I am going to concur with TScar.......I use a portland/water mix to_ grease _the backs of coping/cap stones, where it acts as a bonding agent. I applaud your masonry experience, but for most masons who do it professionally, your experience is perhaps a month of work. I'm not going to argue that your 'aquarium' is anything other than you describe it, and I'm happy that it doesn't leak. But almost _nowhere_ is that an accepted use of a portland slurry.....There are a million products that would be better for that application, I would think that in the future, you would steer someone towards a more accepted and reliable product, your good luck notwithstanding.......


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## Waterbug

JBM said:


> I dont lay much bluestone in an upright position.


Just checking to make sure I understand. Thanks


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## Tscarborough

If portland cement slurry were waterproof, why would there be so many (expensive) admixtures available to make it waterproof?


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## 2low4nh

well if you buy iron clad type N mortar it has a waterproofing agent added to the mix.


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## Tscarborough

There are proprietary mixes containing portland cement that are waterproof, but portland cement as defined by ASTM C-150 does not define or require that as a feature. I checked out the MSDS for St Mary cement, and it has nothing out of the ordinary that would make it waterproof, I would suggest that if possible you check with your father to make sure that he didn't use an "old mason's trick" and add something to the plaster on those aquariums, like a stearate or marble dust.


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## JBM

2low4nh said:


> well if you buy iron clad type N mortar it has a waterproofing agent added to the mix.


And yet it gets darker when you hose it, weird :whistling


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