Bricks, Masonry, Asphalt and Concrete - Use masonry cement for porch foundation?

I'm sure this question is elementary to many; however, my knowledge about concrete stops right around the fact that it is hard.

I need to provide a foundation for some porch columns (6x6 p.t.). The plan is to dig holes and pour concrete in the bottom. After cured, porch will be built. I was going to use 80 lb sacks of premixed concrete mix.

Enter the masonry cement. I have 6 bags of leftover masonry cement, a small pile of sand, and a supply of #57 crushed stone.

Will this work for my foundations? If so, any suggestions on mixing ratio?

type s will set pretty hard. type n not quite as. neither is portland but id use em. i'd go 1-1-1. the sand ratio is usually higher but thats for workability and sacrifices some strength. mix it sticky. throw in a few rods pieces if you have any.

You should be fine with the masonry cement, just mix it the same by volume (portland is 94#, type S is 75#, Type N is 70#).

Do you have masonry cement or do you have masonry mortar? You definitely do not have someting good for concrete. If you have masonry mortar (pre-blended masonry cement and sand), do not use it!

Actual masonry cement contains portland cement and the addition of lime, fly ash, limestone fines or other unknown materials. You could have any or all of the materials added to the portland cement. This will never give you the same concrete as portland cement. It will always be weaker and more absorptive. It is formulated specifically for mortar, where plasticity and workability are the goals instead of strength and low absorption.

The Types S and N referred to are for laying brick or block and not concrete. Type S and N mortars are lower in strength and have more additives for workability than Type M. These are all for mortar and not concrete.

The mix will not meet any code requirements for minimum properties, but if you are only looking for a filler under and around some wood posts, it might be usable.

Just a warning -

Dick

ConcreteMasonry, I run tests on bagged concrete on a monthly basis. It seldom breaks over what Type S will, and that is without the addition of aggregate (in the masonry). Type S masonry cement, mixed in porportion with sharp aggregate and sand will easily hit required strength values for residential footings.

Tscarborough -

Just an academic question - very interesting results

Do you test with the same methods and sample size (aspect ratio, etc.), loading rates, capping and cured in the same manner?

A short, squat mortar test cannot be compared to a concrete cylinder test because of the different failure modes. A short sample measures direct compression or even confined bearing, while a concrete cylinder actually measures the diagonal tension from a shear failure. This is the same problem as trying to compare brick, concrete block and paver compressive strengths.

Dick

The tests are done according to their respective standards which are indeed different. The point is that no matter what the test, you only need a couple of hundred PSI compressive for that application, so both exceed the requirement by several degrees of magnitude.

Agreed that it is adequate for this application, but it does really not equal the knit-picking details (if you can find them) of a code for this application.

This is the problem with the ASTM product and sampling/testing standards. You can never get any comparable results to directly compare products. Mortar and concrete have different test methods that give different results. The only way is to use composite tests, like prisms.

We made 4500 psi (f'm) hollow block prisms with 2500 psi mortar - All you need is high strength block because the mortar has little effect on compressive strength of a wall. - That makes you think!!

Dick

I have to argue daily with engineers and architects about their mis-use of C270 standards on mortar. It is stupid that masons are required to utilize a mortar that is totally unsuitable for the material being laid to satisfy a reqirement that is simply not understood by educated engineers.

I always win, because it is clear in the specification, but it is sad that I have to make the argument.

Keep up with the battle working with people (tradesmen and professionals) that are too specialized and do not look at big picture.

All you can do is hope is that they listen with their mouth shut or talk with their ears open and that they think about what you said or showed them later in on the day.

It is always easy for people to take a strong position on a narrow subject.

You are never wrong going by the code, but you may not be right.

Dick

<I have 6 bags of leftover masonry cement> (says Frank29)

Both of you guys know your stuff here but the above may speak volumes. How old is this stuff anyway? I have had people try to get me to use stuff that has been sitting around for years, laying around on a concrete floor. You could hit it with a sledge and it would bounce off. My own choice would involve something that is six months or less old and has been properly stored. A simple test for me when I pick mortar or Portland up at thee lumber yard is to roll the bag on it's side and shake it down. If the stuff shakes free readily i assume it's fresh.

As for using mortar in place of Portland for a footing that a 6" X 6" column rests on. I spose it could be diluted with some good Portland but it would make darn good backfill too.

bs5

...........How old is this stuff anyway?

It's been at my home 3 days. I had a company build a rock wall around the base of a new addition. They delivered all the material 3 days ago and built the wall over the last two days.

When they left, I was the proud owner of a rock wall, the bags of cement, and a pile of sand.

BTW, it is type "S".