DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   Building & Construction (
-   -   concrete from mortar (

Wahoo 03-05-2008 06:29 PM

concrete from mortar
Hello, I have a bunch of bags of type S mortar laying around and I want to use them to pour a 40 sqft x 4" slab. I am wondering if any of you know a sand/gravel ratio for turning mortar into concrte? Thanks

Tscarborough 03-05-2008 07:40 PM

Bad idea. Masonry cement is not the same as portland cement, and there is no formula for turning it into concrete.

Wahoo 03-05-2008 11:17 PM

thank you, but definitly not what I wanted to hear. I would love more details on why not if you have them for curiosity sake. Anybody want to buy 15 bags or so bags of type S mortar. LOL.

Wahoo 03-05-2008 11:27 PM

And why I am at it would anyone like to tell me the proper receipt for concrete from scratch.

Bondo 03-06-2008 08:49 AM


would anyone like to tell me the proper receipt for concrete from scratch.

1, 2, 3......
1 part Portland,....
2 parts Sand,.....
3 parts Stone.....

terri_and_jj 03-06-2008 03:17 PM


Originally Posted by Tscarborough (Post 104627)
Bad idea. Masonry cement is not the same as portland cement, and there is no formula for turning it into concrete.

I think you are confused here. Type S mortar definetly has portland cement in it. the biggest difference between type s mortar and concrete is the mortar has no stones and about 3x more sand. s-mortar only reaches a compressive strength of about 1800 psi, but thats laregely because more water is added, along with the lack of aggregate

I honestly think you could turn mortar into concrete by simply adding more portland cement and stone. if i have trouble sleeping tonight and the wife won't indulge me, i'll try to sit down and calcualted the proper proportions

ncgrogan 03-06-2008 04:59 PM

Theres an art/science to making concrete..depends on what your doing with it. Is it for a side walk or a nuclear plant. Theres equations to get the right proportions for the psi you want. Then theres the admixtures. Some people spend their entire careers studying/researching concrete mixes. Don't dumb it down too much.

terri_and_jj 03-06-2008 05:06 PM


Originally Posted by ncgrogan (Post 104900)
Don't dumb it down too much.

i think he mentioned in his question that he is pouring a patio slab, not rebuilding the twin towers. we are only talking about a dumbed down exposed aggregate mix. Don't over anyalize it too much either

ncgrogan 03-06-2008 05:08 PM


Originally Posted by Wahoo (Post 104679)
And why I am at it would anyone like to tell me the proper receipt for concrete from scratch.

sounds pretty general to me

concretemasonry 03-06-2008 05:40 PM

concrete from mortar
terri - You are the one that is confused. It is a good thing that you said "I think" instead of "I KNOW".

Concrete has portland cement in it.

Type S mortar (ASTM C270) does not have necessarily have Portland cement (ASTM C150) in it. It may be Portland cement, masonry cement or mortar cement. If it has Portland cement in it, it must also have other components (fillers, lime, some fly ashes, soap, etc.) that are not necessarily acceptable in concrete, but are needed in mortar.

In addition, the sand in the mortar is too fine for good concrete, so just adding rock will not solve all the deficiencies.

Type S mortar has a required compressive strength of 1800 psi, but it is tested in a way different from concrete. It is not just because of the water. This method of testing does not give an equivalent value and gives an overstated strength by comparison. The purpose of good mortar is not compressive strength, but to have the properties of workability, ductility and bond. (ASTM C270 - Appendix)

Any good durable concrete should be 2500-3000 psi (if not 4000 psi) and not 1800 to last. It is not a question of the structural strength, but the other properties that follow with an accepatable concrete compressive strength.

A requirement of a patio slab if for it to look good and be durable. If you have freezing, a botched up mix of some Type S mortar, a few rock and maybe a little Portland cement could be a lot of work to tear out and replace in a year or so. The excess of fine sand requires more cement and water which will give you shrinkage cracks and poor durability even for foot traffic.

It is hard to beat the economy of a 1:2:3 mix if you use the right materials.

terri_and_jj 03-06-2008 05:59 PM

you obviously seem to know more about this than i do, but i will say that i have never personaly used a type s mortar that does not contain portland, that much I DO KNOW. Regardless, the only real concern is whether or not the bags HE HAS contain portland, which a quick look at the bag would easily put an end to that debate.

I am a big believer in doing the job right the first time, but for something like this, a simple pad that will require 30 total bags, of which he already has 15 bags, and the biggest problem if it fails is that it will have to be cleaned up and redone, i'd personally give it whirl. simply adding too much water to standard concrete mix could result in the exact same freezing situation you described

He asked for opinions, and my opinion is for this application it can be done with the addition of portland and stone.

concretemasonry 03-06-2008 09:52 PM

concrete from mortar
Looking at the bag will not tell you what it contains. The label only says Type S. There are also other types - Type M and Type N. The original supposedly comes from the word MaSoNry.

To meet the requirements of a specific type, the mixture must meet the proportion requirements of different combinations of cement, lime and other materials. An alternate method is to have it meet the property requirements for different uses.

Some suppliers may supply a mixture of Portland cement, lime and masons sand (not concrete sand). Most is usualy a mixture of either masonry or mortar cement and various additives to give the cement the proper workability. Strength is one method used to classify cement, but it is not the best measure. The rule is to use the weakest mortar possible and still carry the loads. This will usually permit the use of a more workable mortar.

The fine sand (masonry) has more surface area and requires more cement and water than normal concrete.

Since he has to buy additional material, I would suggest selling the bags of mortar that he has to mason and buying a prepackage concrete mix. This will give uniformity of strength and color.

terri_and_jj 03-07-2008 09:12 AM

Interesting. Thanks. i've always been under the impression that ALL modern mortars, except L mortar, use portland cement. I also was under the impression that this is an ASTM standard, so in otherwords ALL premixed type M is 3 parts portland, 1 part lime and 12 parts sand, and ALL type S is 2 parts portland, 1 lime, and 9 sand.

one question for you, and if it sounds like i am being sarcastic, please know that i am not at all, just sincerely curious. You mentioned that the sand used in mortar mix has more surface area and requires more cement. This sounds great, but i have always been under the impression that there is LESS cement and MORE sand in a mortar, vs an equal amount of concrete. so if a yard of S mortar contains 423 lbs of portalnd and 1620 pounds of sand while the average patio mix has 564 pounds of portland and only 800 pounds of sand

concretemasonry 03-07-2008 01:44 PM

Anytime you mix cement and aggregate, the more surface area of the aggregate you have, the more cement that is required to coat all of the particles and tie them together. The extra cement requires extra water to make mortar more usable.

It is difficult to compare mortar with concrete because they are designed to do different things. Mortar is desired to be workable, have good bond and have adequate strength, but the mortar strength is not too important in the compressive strength of a masonry wall (the units used are by far the most important factor). You can make a 4500 psi block prism (2 block and mortar) using 1900 or 2500 psi mortar because it is a thin layer between high strength block.

Concrete requires the right gradation (size mixture) of aggregates to minimize the amount of cement for a given strength. Bad gradations will require more cement. The cement requires water to hydrate, but also causes shrinkage.That is one of the reasons for a maximum slump (usually 3-4 inches).

In practice, concrete materials (cement, sand, aggregate) are weighed out and compensated for the water they contain, but in a plant they are batched by WEIGHT. For mortar, everything is specified by volume. The amount of aggregate is usually 2 1/4 to 3 times the VOLUME of the cementitious materials.

kgphoto 03-08-2008 12:15 AM


Originally Posted by terri_and_jj (Post 105088)
Interesting. Thanks. i've always been under the impression that ALL modern mortars, except L mortar, use portland cement.

While it may be true that most contain Portland cement, they also contain the other stuff that changes the PSI and other characteristics making it unsuitable for the slab.

All times are GMT -5. The time now is 07:56 PM.