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Old 06-12-2017, 03:41 PM   #1
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Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


Hi everyone,

So we are adding a small extension to our existing house. The size is 2ft out and 36ft long (the run of the kitchen and bedroom). The existing foundation is block wtih a footer. It is 4 foot in height (About a foot above the ground). The footer & rebar have been poured and is ready for block work.

Now for the mortar, looks like we have to use Type "S". Our local home store has Sakrete in stock. I am left wondering if this is the most affordable route or should I get portland, and sand and mix my own mix? We have a cement mixer on hand which would would use in either case scenario.

Eventually the wall will be parged and sealed as the old wall was as well.
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Old 06-12-2017, 06:34 PM   #2
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


You don't use portland cement. You use masonry cement. Mixing your own will be cheaper.
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Old 06-12-2017, 07:14 PM   #3
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


You can use either a prepackaged masonry cement or use a Portland Cement and lime mixture to get a Type S mortar. The same applies, with different ratios for Types M (the strongest) and Type (weaker) that are sold prepackaged.

The ASTM mortar specifications (Appendix note 1) recommend that you use the weakest mortar possible for the structural loads. - Your loads are minimal. The reason is that workability is the most important factor in the choice of mortar. Mortar is not the controlling factor in most structural situations.

In most applications filling block solid is not necessary and removes some of the advantages of concrete block (CMUs) construction. I have seen 22 story buildings built out of 6" hollow block that had only one core filled and reinforced every 4' according to the U.S. codes.

Dick
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Old 06-12-2017, 07:25 PM   #4
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


Thanks for the reply fella's! My father in-law mentioned 1 part masonry cement or portland, 1 part lime, 4-6 parts mortar sand (Not sure if that means multi purpose sand)?

Concretemasonry, since you mentioned load. As I mentioned basically adding that outside wall and adding 32 inches of extra space to the living area but we will also be adding a second floor down the road. I have rebar every 4ft and 4ft high per local code. I planned on filling every 4 feet and the corners. I'm curious as to why filling all the block is a disadvantage (Just from a knowledge perspective).

I have read a few reviews that the pre mixed mortar doesn't have good hold power because they tend to add too much sand. That leaves me with trying to figure out where to buy non bagged so I can mix it myself. Big box store just sells the premix from what I recall.
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Old 06-13-2017, 06:05 PM   #5
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


Pre-mix mud is hit or miss, and is also territorial. It's bagged regionally with local materials to save on shipping costs, so it's not the same from one area to the next. Personally, I prefer SPec-Mix over anything that Quikcrete bags, even though they're the same parent company. I'd look for this if you can find it.

http://www.specmix.com/product/portl...e-sand-mortar/

Anything we lay below grade (which will be subjected to moisture) we use Type M, as that's what it's intended purpose is. Also, to give you an idea, one 80# bag of masonry cement (like Type M) will yield ob 4-5 pre-mix 80# bags.

When grouting, I'd recommend only filling the cores with rebar as well, and make sure the grout is WET so it fills everything in well. Grout doesn't need to be nearly as strong as the mortar to serve it's purpose.
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Old 06-13-2017, 07:37 PM   #6
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


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Originally Posted by jomama45 View Post
Pre-mix mud is hit or miss, and is also territorial. It's bagged regionally with local materials to save on shipping costs, so it's not the same from one area to the next. Personally, I prefer SPec-Mix over anything that Quikcrete bags, even though they're the same parent company. I'd look for this if you can find it.

http://www.specmix.com/product/portl...e-sand-mortar/

Anything we lay below grade (which will be subjected to moisture) we use Type M, as that's what it's intended purpose is. Also, to give you an idea, one 80# bag of masonry cement (like Type M) will yield ob 4-5 pre-mix 80# bags.

When grouting, I'd recommend only filling the cores with rebar as well, and make sure the grout is WET so it fills everything in well. Grout doesn't need to be nearly as strong as the mortar to serve it's purpose.
Thanks jomama, those are some interesting points you make. According to my book for the mortar mix is:
1 part masonry cement (straight not pre-blended)
2-3 parts masonry sand.

The sand is pretty cheap and the bags of mortar are about 11 bucks. The premixed stuff at the depot is about 5 bucks, so sounds like its cheaper to mix my own. I'll def look to see what brand the local stores are selling.

Question. I called up 2 local mason supplies in the area. 1 place sells 1 ton bags of mason sand for $55 bucks. The second place sells 1 yard bags for $50. Is there a difference between these two bags? What do masons usually ask for?

My calculator application is giving this for material calculations:
42ft x 4ft = 189 blocks (8 x 8 x 16)
6 - 75 Lbs bags of masonry cement
18 cubic feet or 1 tons of masonry sand <-- this is the confusing part

Also you mentioned filling the rebar cavities. Straight cement in those holes? Do you know why its best to just seal the rebar cavities and not the rest? No basement in this area mind you.
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Old 06-13-2017, 11:14 PM   #7
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


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Thanks jomama, those are some interesting points you make. According to my book for the mortar mix is:
1 part masonry cement (straight not pre-blended)
2-3 parts masonry sand.

Not sure what you're calling "pre-blended", but by definition a masonry cement should be pre-blended, Portland cement & lime was the traditional way, and can still be found. We tend to use 3 - 3.5 parts sand to our masonry cement, but we have a little bit of experience with mortar.

The sand is pretty cheap and the bags of mortar are about 11 bucks. The premixed stuff at the depot is about 5 bucks, so sounds like its cheaper to mix my own. I'll def look to see what brand the local stores are selling.

Question. I called up 2 local mason supplies in the area. 1 place sells 1 ton bags of mason sand for $55 bucks. The second place sells 1 yard bags for $50. Is there a difference between these two bags? What do masons usually ask for?

Most masons have their own dump truck, so they probably don't but "super-sacks" or bags of sand. As a general referance, mason sand will weigh anywhere from 2500#s (very dry) to about 3000#'s per yard.

My calculator application is giving this for material calculations:
42ft x 4ft = 189 blocks (8 x 8 x 16)
6 - 75 Lbs bags of masonry cement
18 cubic feet or 1 tons of masonry sand <-- this is the confusing part


Way too late in the evening for math, but again, generally speaking, I figure about 55 8" block per batch (site mixed, not pre-mix)
that aren't backplastered. On basements, I used to figure 40-45 block per batch with back plaster included. That number can vary widely, and as a DIY'er, I wouldn't be surprised if you used twice the mortar that we do because of the additional waste attributed to the learning curve.


Also you mentioned filling the rebar cavities. Straight cement in those holes? Do you know why its best to just seal the rebar cavities and not the rest? No basement in this area mind you.
We use almost straight Portland cement and sand(torpedo sand preferably) for pilasters. We usually carry some Type N or S that doesn't have any lime in it to help to keep the grout from separating as well. The reason we try to avoid lime is because it is well documented that it will accelerate corrosion of the rebar, and any steel, it comes into contact with.

Lastly, reasons not to grout non-re-enforced block cells:

- Waste of time and materials with little to no benefit.
- Shrinkage from grout transfers through block and compromises block wall strength.
- Additional weight on the footing that doesn't need to be there. (Note where Dick mentioned above about "minimal loading". What he's getting at is that conventional wood framing weighs nothing compared to the foundation, and should be considered "lightweight". I've been known to tell framing carpenters on a new house that we spent a week getting the first half of a million pounds of house in place, it should only take them 2 days to get the next 150,000 pounds installed.)
- Maybe not applicable in your case, but the interior withe of block is a great place to control any water that leaks through, and it's harder to do that with grout in the way.
- It's a waste of valuable resources. I'm not that old,but I've lived through a cement shortage already, no sense in adding to a possible temporary shortfall of raw material for no benefit.
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Old 06-14-2017, 12:43 PM   #8
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


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Originally Posted by jomama45 View Post
We use almost straight Portland cement and sand(torpedo sand preferably) for pilasters. We usually carry some Type N or S that doesn't have any lime in it to help to keep the grout from separating as well. The reason we try to avoid lime is because it is well documented that it will accelerate corrosion of the rebar, and any steel, it comes into contact with.

Lastly, reasons not to grout non-re-enforced block cells:

- Waste of time and materials with little to no benefit.
- Shrinkage from grout transfers through block and compromises block wall strength.
- Additional weight on the footing that doesn't need to be there. (Note where Dick mentioned above about "minimal loading". What he's getting at is that conventional wood framing weighs nothing compared to the foundation, and should be considered "lightweight". I've been known to tell framing carpenters on a new house that we spent a week getting the first half of a million pounds of house in place, it should only take them 2 days to get the next 150,000 pounds installed.)
- Maybe not applicable in your case, but the interior withe of block is a great place to control any water that leaks through, and it's harder to do that with grout in the way.
- It's a waste of valuable resources. I'm not that old,but I've lived through a cement shortage already, no sense in adding to a possible temporary shortfall of raw material for no benefit.
Thanks for the in-depth knowledge!

By "pre-blended" I mean't the stuff the depot carries that does not need any sand, just add water.

So based on everything that has been stated I am going to ge 6 bags of "M" type mortar and a ton of sand. Then mix 1 part type "M" to 3 parts of masonry sand.

I will also just grout the cells that have rebar running inside of them. So if type "M" mortar has lime in it, does it make more sense to grout the rebar cells with regular premixed high strength concrete like sakrete instead?
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Old 06-14-2017, 12:52 PM   #9
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Re: Cement Block Foundation Wall - Mortar Mix Buying Bags Versus Mixing


I think I would fill the cells with concrete, not mortar. Concrete has more strength.
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