# concrete wall question



## fishhead (Jul 19, 2006)

I'm always looking for construction methods that I can do and that are cheap but effective so I've been wondering if a person could replace some of the concrete in a wall with crushed rock. I'm thinking of using 3/4" minus crushed rock.

Could a person replace 75%? 90%? of the concrete in a wall with crushed rock. Crushed rock is about 10% of the cost of concrete I think so if a person could replace it with rock it would help lower the cost of the wall.


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## Bearfootfarm (Jul 13, 2006)

> Could a person replace 75%? 90%? of the concrete in a wall with crushed rock.


Yes, if you're willing to lose 75%=90% of the STRENGTH of the wall, and risk having it turn into an expensvie pile of rocks.

You won't "save money" *reengineering proven technology*


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## Darren (May 10, 2002)

Concrete is a mixture of cement, sand and aggregate. Aggregate is crushed rock although sometimes rounded river gravel is used.


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## fishhead (Jul 19, 2006)

Is there a way to adjust the mixture to accomodate more aggregate?


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## Darren (May 10, 2002)

It really depends on what you're building and what it's holding up. Retaining walls are examples of construction that lots of people screw up. I'd do an internet search on concrete mix design.


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## fishhead (Jul 19, 2006)

I'm just going on seeing rock walls that are mostly rock with concrete holding them together.


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## jwal10 (Jun 5, 2010)

Rock walls use mortar to hold them together, Rocks are strong and the mortar is just as strong. Concrete has rock for the aggregate with cement and sand for strength, less cement, less strength.

Now if you want to use bigger rocks, they can be mortared together to build walls....James


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## fishhead (Jul 19, 2006)

Isn't mortar just a different mixture of cement?

Could a person make a wall out of mortar and crushed rock with rock replacing at least 1/2 of the mortar?


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## Bearfootfarm (Jul 13, 2006)

> Isn't mortar just a different mixture of* cement?*


You're confusing "cement" with "conrete"

(Portland) Cement is the gray powder you mix with sand and water to make "mortar"

If you add small rock (aggragate) to the mortar, THEN you have "concrete"

Don't go trying to reinvent the recipe just to save a few pennies, because you won't be happy with the results


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## jwal10 (Jun 5, 2010)

It would take more mortar (cement). Concrete IS cement, sand AND aggregate (rock). All mixed together, more rock, weaker concrete. Too much rock, no wall. Have you ever seen concrete that wasn't mixed well? The concrete falls apart because the cement didn't hold everything together....James


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## joebill (Mar 2, 2013)

there are options for saving money, and they do work, at least hereabouts. We pour concrete here, then load it up with cobbles, except on the surface where it needs to be smooth. When you talk about "crushed rock", though, I suspect you are talking about gravel sized rock which would coarsen the mix and lessen the percentage of sand which helps the stuff bind together.

There is a very old structure down the valley from me that is still intact and demonstrates what one can and cannot do pretty well. It was built, ovbviously, by using slip forms. That is, two boards around a foot apart and a foot tall, then pouring a section of wall, then moving the boards up and doing it again. Every time they moved the boards up, they piled rocks on top of the previous pour and poured concrete around them. Worked fine, EXCEPT.....Some places they put the rocks too close to the forming boards and the concrete didn't make it all the way into the cracks, so the wall is rough in places with the rocks showing through the gaps in the concrete. Other places, they used dry, pourus rock that soaked up the water in the concrete too quick and it didn't have time to cure, so the surface was weak and sloughed off, making more rough stuff.

If you are going to do it this way, it's better to do the pour, then dump wet cobbles of good, hard stone into the top of the form and let it bring the level of concrete up to the top.

All this is only in my opinion and experience. It's also in an area where the ground does not freeze an inch below the ground. We did pour a fair amount of concrete this way (loaded with rock) in the Midwest 50 years ago, and they had the devil's own time getting it out 10 years ago, so I place a certain amount of faith in it, but don't really care to argue about it....joe


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## Evons hubby (Oct 3, 2005)

fishhead said:


> Is there a way to adjust the mixture to accomodate more aggregate?


Yes, but you sacrifice strength. The standard "five bag" mix has proven itself to be about the best deal for the money/quality of product ratio. That is using 5 bags of portland cement per cubic yard of concrete. For most common concrete applications you use a 1-2-3 mixture by volume.. one part cement, 2 parts sand and 3 parts gravel. You can also gain a lot of strength by adding fiberglass and steel reinforcement. Again however these items cost money too.


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## joebill (Mar 2, 2013)

fishhead said:


> Isn't mortar just a different mixture of cement?
> 
> Could a person make a wall out of mortar and crushed rock with rock replacing at least 1/2 of the mortar?


Here, you are talking about rock masonry and if you have lots of sizable rock and a fair amount of time, you can learn it and do it very cheap and very well. It takes some time and study, but the rewards are worth it, once you can look at a stone wall you built that will ourlast you by perhaps 100 years.

You can look up pictures of stone work done by the ccc boys in big sur park in Califormia during the depression that is still doing very well. My father was one of them....Joe


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## maverickxxx (Jan 25, 2011)

If you are building a retaining wall then why don't you use gabion baskets with larger stone about baseball softball size.


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## fishhead (Jul 19, 2006)

What's a gabion basket?

I was wondering if a guy could just vibrate in some 3/4" minus crushed rock. That should eliminate the air spaces and allow the cement to fill them in.


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## Bearfootfarm (Jul 13, 2006)

> I was wondering if a guy could just vibrate in some 3/4" minus crushed rock. That should eliminate the air spaces and allow the cement to fill them in.


If you start changing the* ratios* of the mix, you change the strength of the end product.

Vibrating is done to make sure the forms get filled completely


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## hippie (Aug 21, 2012)

Bearfootfarm said:


> You're confusing "cement" with "conrete"
> 
> (Portland) Cement is the gray powder you mix with sand and water to make "mortar"
> 
> ...


The difference in cement and mortar is Mortar has lime in it and cement doesn't. They make different strengths of mortar N- Weakest, S- Medium- M- Strongest.


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## fishhead (Jul 19, 2006)

How can a rock wall be so strong when it's got a mix ratio that is skewed towards more rock than mortar?


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## farminghandyman (Mar 4, 2005)

a lot of concrete is mad of crushed rock, in some locations if it is not crushed sharp rock it will not pass inspections, 

the rock is the base, the sand is the filler between rock nd the cement is the glue,

the basic mix for general size gravel is a 5 to 1 mix, 
on concrete with crushed rock is 3 rock -2 sand -1 cement

the mix is for mortar is 3 sand to 1 cement product, (cement /lime/other)

Concrete is much like the demonstration below,



> http://www.lancaster.edu.mx/lancaster/Students/GRADUATION_SPEECH_2008.htm
> _Without saying a word to his students, he removed the lid of the jar and filled it with golf balls. When no more golf balls fit he closed the jar with its lid. He then asked his class, &#8220;Would you say that the jar is now full?&#8221; His students observed the jar and concluded that the jar was indeed full._
> _The professor then proceeded to open the jar up and started inserting marbles into the jar. The marbles started to fill the gaps between the golf balls. After sealing the jar, he asked his class once again if they thought the jar was now full. The class concluded that the jar was indeed now full._
> _The professor opened the jar a third time and started pouring in sand. Obviously, the sand started filling the gaps between the golf balls and the marbles. He then sealed the jar and asked his class a third time if the jar was full. His class chuckled and replied in unison, &#8220;Yes, it is now full!&#8221;_
> _The professor opened the jar and emptied two small cups of coffee in the jar. The liquid had completely filled the gap between the golf balls, the marbles, and the grains of sand. He then began his lecture._


if you do not have enough rock then it will take more sand and cment to glue the sand together, so the ratios are important to follow, 

I have seen if some one has large rock (3 to 6 inches across) to drop them in the forms when pouring the wall kinda like a rock wall but in a form and complete cement cover, 
the did this a lot in the 1930's during the depression, probably would not pass modern building codes,

the rock is the strong part of the concrete,


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## Bearfootfarm (Jul 13, 2006)

hippie said:


> The difference in cement and mortar is Mortar has lime in it and cement doesn't. They make different strengths of mortar N- Weakest, S- Medium- M- Strongest.


"Cement" means Portland Cement, which DOES have lime
"Mortar" is Portland Cement and Sand
"Concrete" is Portland Cement, Sand, and an aggregate (the rock in this case)


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## Bearfootfarm (Jul 13, 2006)

> How can *a rock wall* be so strong when it's got a* mix ratio* that is skewed towards more rock than mortar?


"Rock walls" are *layed like bricks*, with mortar filling the gaps
There is no "mix ratio" for anything except the Mortar

"Concrete" is poured like a thick mud
The *terms aren't interchangable*


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## fishhead (Jul 19, 2006)

farminghandyman said:


> a lot of concrete is mad of crushed rock, in some locations if it is not crushed sharp rock it will not pass inspections,
> 
> the rock is the base, the sand is the filler between rock nd the cement is the glue,
> 
> ...



That's what I had in mind with the crushed rock only I would vibrate it to eliminate as many air pockets as possible. I don't care what it's called, mortar, concrete or cement.


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## Bearfootfarm (Jul 13, 2006)

> I don't care what it's called, mortar, concrete or cement.


You need to care if you want people to answer your questions, since they are three *different* things :shrug:


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## maverickxxx (Jan 25, 2011)

To much vibrating will cause the mix to seprate. It won't wrk. When u vibrate concrete it's only for short bursts to cause air to rise to top. To much vibrating an stone all goes to bottom then a really sandy layer an mostly pure cement on the top. The reason what u want to do will not wrk is the cement an sand will not fill all the voids no matter how wet it's poured. Two it would be so diluted with water that the cement would be washed an prolly alot of the sand an would be extremely weak an prolly crumble as soon as forms where off. Also u would need to have tons of rebar in that to hold it together cause it would crack an crumble. 
Gabion baskets are a wire basket that gets filled with rock an stacked on top of each other like rectangular blocks. 
U can see them along highways to help hold slopes back along rivers also in drainage areas so water can pass through but not dirt.


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## fishhead (Jul 19, 2006)

It sounds like it would be best to use large rocks to make it easier to get the mix in the empty spaces and be careful fill in all the voids. Large rocks would still be cheaper than cement and pretty bulletproof.


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## Bearfootfarm (Jul 13, 2006)

> It sounds like it would be best to use *large rocks* to make it easier to get the mix in the empty spaces and be careful fill in all the voids.* Large rocks* would still be *cheaper *than cement and pretty bulletproof.


LOL
Go for it then, but don't say you weren't warned when it collapses on you, and you spend three times as much to redo it all


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## hippie (Aug 21, 2012)

You're confusing "cement" with "conrete"

(Portland) Cement is the gray powder you mix with sand and water to make "mortar"

If you add small rock (aggragate) to the mortar, THEN you have "concrete"

Don't go trying to reinvent the recipe just to save a few pennies, because you won't be happy with the results

Not meaning to highjack thread

Just shows how little you know about cement and mortar. 2 totally different things. You cannot just put stone in mortar and make cement cause it isn't. Concrete is cement+ sand + aggrageate + water=Concrete. Mortar is Cement + Lime + sand + water = Mortar. You can disagree with it all you want been like this for the 40 plus years I have been around it. You put Aprox. 16 shoveis of sand pur bag of mortar for type N 17 shovels for S 18 shovels for M. Concrete goes bags per yard depending on what strength you want concrete.


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## fishhead (Jul 19, 2006)

Thanks for the info.

Are rock walls very strong as far as load bearing?


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## joebill (Mar 2, 2013)

They are very strong indeed. You need to read up on them a bit, and your location probably will require a footing because of the freezing. You'll need the footing to go below the frost line, if I'm not mistaken. I'm a desert dweller, so not real bright about cold area rock masonry.

http://www.parks.ca.gov/?page_id=24877

That site shows pictures of a bridge built by my father and others during the great depression, with the footings etc. built by rock masonry, still standing and in good shape. You probably can find rock walls and buildings in your area that are even older. They will support great loads, but you need to educate yourself how to build them and how wide/deep the footings need to be in cold areas.

Lots of books out there about rock masonry.......Joe


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## Bearfootfarm (Jul 13, 2006)

> You cannot just *put stone in mortar and make cement* cause it isn't.


No one said that at all


> You can disagree with it all you want been like this for the 40 plus years I have been around it.


Most people buy "mortar mix" now
Very few actually blend their own mortar, and it's obvious Fishhead is using three different terms interchangably.

Regardless of the precise "recipe" his plan to add lots of "big rocks" to "cement" and "vibrate it" will NOT produce a desirable end result


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## hippie (Aug 21, 2012)

Sorry Bearfootfarm thought that's what you were referring to in Post#9 was just trying to right the bad info. 

*Portland Cement, Lime and Sand*
There are a *variety of mortar mixes* that the mason contractor can mix up, depending on the type of material that is being installed:



This is the &#8220;old school&#8221; method, the standard for the industry that all other methods are compared to. In order to make a masonry mortar one would proportion the materials into the mixer in this manner; 

1 bag 
94# of Portland Cement Â½ bag50# Hydrated Lime 28 &#8220;Shovels&#8221;Masonry Sand 7 to 8 GallonsClean Water

*Mixing Procedure:*



Put 2/3 to 3/4 of the water into the mixer
Add the Portland Cement and Hydrated Lime to the batch
Add the sand into the mixer, adding water as necessary to achieve the desired consistency
Mix for 5 minutes in a mechanical paddle type mixer
Amount of water required to make good mortar will vary depending on the desired consistency of the mortar. For stiff mortar use less water, for wet mortar use more water. If you do not add enough water the mortar is so stiff that it is unworkable and very difficult to use, if you add too much water the mortar turns to &#8220;soup&#8221; and you will be unable to use it

*Masonry Cement*

Masonry Cement is simply a product that has Portland Cement and Hydrated Lime already blended together in the proper proportions. In order to make a Type S mortar with Masonry Cement one would proportion the materials into the mixer in this manner:

1 bag70# or 78# Masonry Cement 18 to 20 &#8220;Shovels&#8221;Masonry Sand This varies with sharpness of sand And there nice rounded shovels. 5 GallonsClean Water 
*Mixing Procedure:*



Put 2/3 to 3/4 of the water into the mixer
Add the Masonry Cement to the batch
Add the sand into the mixer, adding water as necessary to achieve the desired consistency
Mix for 5 minutes in a mechanical paddle type mixer
Add water to achieve desired consistency of mortar, less water for stiff mortar, more water for wet mortar. 





* 

Bagged Mortar Types and breaking strengths after cured. 

Type M (2500 psi) 
Type S (1800 psi) 
Type N (750 psi
**Pre-mixed Mortar*

This is the easiest mortar of all to make. Pre-mixed mortar is a combination of Portland Cement, Hydrated Lime, and Masonry Sand already blended together in the proper proportions to make a Type S mortar. All that is needed is to add sufficient water to achieve the desired consistency, usually about 5 to 6 quarts for an 80# bag. Pre-mixed mortars are a little unique in that they require a slightly modified mixing procedure.

*Mixing Procedure *



Put 2/3 to 3/4 of the water into the mixer
Add the Pre-mixed mortar into the mixer, adding water as necessary to achieve the desired consistency
Mix for 3 to5 minutes, turn off the mixer and allow mortar to &#8220;slake&#8221; for 2 to 3 minutes, re-start the mixer and mix for an additional 2 to 3 minutes adding water as necessary to achieve desired consistency.
Pre-mixed mortars use a kiln dried sand that has a higher water demand. It takes a few minutes for all of the water to be absorbed into the dry sand, hence the need for a prolonged mixing time. If you do not allow the mortar to set and &#8220;slake&#8221;, it will feel gritty on the trowel and will be difficult to work with.

All of these mortar may be mixed by hand in a wheelbarrow or &#8220;mud tub&#8221; for those of us who do not own a mixer. A mortar hoe is a great tool when mixing by hand, as well as the obligatory square point shovel. I have found from past experience that a standard construction grade wheelbarrow is too small to mix a full bag of Portland Cement, Â½ bag of Hydrated Lime and 28 shovels of sand. It will just barely fit 1 bag of Masonry Cement and 18 to 20 shovels of sand. A standard wheelbarrow very comfortable fits 3 of the 60# bags of Pre-mixed Mortar, or 2 of the 80# or 94# bags of Pre-mix Mortar. Follow the same mixing procedures as when using a mechanical paddle mixer.


If I understand what you are trying to accomplish. No you cant replace the concrete with stone, well you can but as Bearfootfarmer said you will lose strength. Can you repair the wall by simply laying field stone in like you were doing a stone wall using type M mortar between the stone witch should be plenty strong enough I would think. . Is it top of wall middle of wall Do you have pictures of the wall to be repaired. There are a lot of different variables so without seeing pictures its hard for me to say for sure. Hope this helps.


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## fishhead (Jul 19, 2006)

Thanks for the info.

Actually I'm just trying to learn for the future in case I want to build a strong wall for a building.

If I'm understanding this I cannot use mortar to fill in the spaces between crushed rock like 3/4" minus but I can use it in between larger field stone.

My goal would be able to build a wall using mainly cheaper rocks than more expensive mortars. That would reduce the cost of the wall because rocks are cheaper than mortar so you could build a wall with say 75% rock/25% mortar instead of 100% concrete.


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## hippie (Aug 21, 2012)

fishhead "If I'm understanding this I cannot use mortar to fill in the spaces between crushed rock like 3/4" minus but I can use it in between larger field stone."

fishhead "My goal would be able to build a wall using mainly cheaper rocks than more expensive mortars. That would reduce the cost of the wall because rocks are cheaper than mortar so you could build a wall with say 75% rock/25% mortar instead of 100% concrete."


You could it just wouldn't be as strong or last very long. Here in Michigan there are many old Farm houses that have field stone basements. Some of the walls are 20+ inches thick. And when they mixed there mortar it was not bagged mortar, witch if you mix your own mortar it is by far stronger than bagged mortar but more costly. If you ever tried to break mortar from and old building you will know what Im talking about. You cant take cement away or mortar away from anything and have it be as strong. Or if you do you better add reinforcement some place. Then you spent money you saved skimping on the concrete.


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## hippie (Aug 21, 2012)

Plus remember with a wall your dealing with shear strength (sideway force) and possibly hydraulic pressure (pressure from water)


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## fishhead (Jul 19, 2006)

Thanks.


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## joebill (Mar 2, 2013)

I'll add one more thing. For mixing small amounts of mortor at one time, there is nothing as great as the tool that fits in a 1/2" drill motor that's like a paint mixer only heavier duty. mix a 5 gallon bucket of mortor in a minute or less. That eliminates a LOT of hard work and saves a lot of time.

Large batches of mortor tend to set up before they are used, so I mix smaller batches that way, to good effect......Joe


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## hippie (Aug 21, 2012)

Good point joebill for sure the easiest. Usually its 3 to 1 ratio 3 parts sand 1 part mortar and water. A bag of motar will lay approx. 45-50 block or 125 brick


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## jwal10 (Jun 5, 2010)

Big rocks and blocks are mortared (glued) together. With concrete, the materials are the glue (all bound together)....James


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