Sakrete vs. mortar

[VunderBob]

I have a couple of places in my garage foundation that need repairs, meaning I have to replace some cinderblocks; about 5 total.

When I asked about mortar at the nearest Lowe’s, the minimum I could buy was a 50 lb bag, and I don’t need that much. However, I have half a bag of Sakrete sitting in the same garage, and it should be more than sufficient (by quantity) to set the blocks.

Can bagged concrete be used as mortar if I mix it thick enough? Will I have a good joint when I’m done, or will this be an exercise in half-assery?

[beowulff]

Pre-mix concrete has “aggregate” (stones) in it. Mortar only has sand. The stones will make it tough to get a thin layer between blocks…

[Duck_Duck_Goose]

The short version: " Mortar is “sticky” so it adheres to the block, stone or brick. Concrete is designed to stand alone."

The geek talk:

The big difference between concrete, mortar and grout is in their plasticity or fluidity in the initial stage. Mortar is relatively stiff, and if a slump test were made it would have a slump of five to eight inches. Concrete is also relatively stiff with a slump varying from two inches to six inches maximum. The slump of concrete is a controlled requirement for it reflects directly to the water/cement ratio of the concrete mix. This is one major point of variance between concrete and grout. Concrete, with a tightly controlled water/cement ratio, has a relatively low slump, relatively slight plasticity and very low fluidity. This is because all the water in the concrete will stay within the concrete when it is placed in water-tight forms. All the water in the concrete mix is part of the calculation of the water/cement ratio. Also, in concrete, the forms are spread relatively far apart, and the size of member is relatively large compared to the aggregate material, which allows for easy placement. Mortar is plastic material with a low water/cement ratio and high in cement content. Mortar must be relatively stiff in order to be handled on a trowel, to be spread on the masonry unit and to evenly support the masonry units placed on it. This stiffness is required for the masonry wall to be built above without the mortar squashing or squeezing out and deforming. Although mortar has a low water/cement ratio, this ratio is further decreased after the mortar is spread on the bed and the masonry units are placed on it. Any excess water in the mortar is absorbed both down into the masonry unit on which the mortar is spread and up into the masonry unit that is placed on the mortar bed. This absorption helps create bond between the mortar and the masonry unit.

Sounds to me like the Sakrete would just squish out from between the joints and not really effectively hold the blocks together.

[VunderBob]

@beowulff

Pre-mix concrete has “aggregate” (stones) in it. Mortar only has sand. The stones will make it tough to get a thin layer between blocks…

Fair enough. I guess I’ll buy some mortar.

[Duck_Duck_Goose]

You might check at your local TrueValue Hardware to see if they have smaller bags of mortar.

[Philster]

Mortar needs to match the material it is working with. Even different bricks require different mortars, and cinderblocks needs their own. The more things expand and contract alike, the less crumbling/failure will occur.

When you get ready to repair, you should wet the blocks and joints when working with them or they are gonna suck the moisture out of the new mortar, shorten its curing time and weaken it. Could cause you to have a bigger mess.

[cornflakes]

Mortar is softer than concrete and more plastic, thanks to the lime used. It is less likely to crack the block. It’s also stickier, as was said upthread.