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Old 05-26-2011, 06:30 PM   #1
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How thick is too thick for mortar bed in block foundation wall


I'm pulling out a basement window blocking it up and moving a door basement door over. The foundation are blocks above grade and field stone below.
Between the window and the door there's about a six foot opening in the foundation wall. I put a line between the old in the opening to make sure that my new block courses are true to the old. I'm now on the top coarse just below a 4x8 sill.
If I push the block up as far as it will go against the sill I'll end up with about a 3/4 mortar bed that I need to tuck. Is that too thick? The new blocks are slightly smaller than the old foundation blocks (7 5/8 vs slightly more than 7 3/4).
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Old 05-26-2011, 09:03 PM   #2
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How thick is too thick for mortar bed in block foundation wall


I just tried it... it looks fine, just a bit chunky.

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Old 05-26-2011, 09:08 PM   #3
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How thick is too thick for mortar bed in block foundation wall


http://www.myguardian.com/code/morta...rtarJoints.pdf

It is the final shrinkage that seems to be the problem.... but usually only in load-bearing walls.
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Old 05-26-2011, 09:33 PM   #4
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How thick is too thick for mortar bed in block foundation wall


You could be trying to use the modular height block ( 7 - 5/8" high) in a wall that was made useing the fulll 8" (8" high) block that were produced in many market areas.

The extra mortar thickness is not that important except from a visual/appearance situation. Mortar has a minimal effect on the strength of a masonry wall from a design standpoint.

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Old 05-26-2011, 09:48 PM   #5
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How thick is too thick for mortar bed in block foundation wall


I found the old blocks fairly inconsistent. Some of them have a face that is 7 13/16 and a back side of slightly less than 7 5/8, while others are 7 5/8 on both sides. It makes for dropping the blocks in place and leveling them a bit difficult. The thickness of mortar was probably more like 5/8". I noticed that the original had some pretty wide mortar beds in some places as well.
I grouted 4 of the 5 courses with the top course the only ones left hollow because I have to squeeze them in under the sill. What I'm filling in is only 3 blocks wide so I'm not terribly concerned. I just don't want to do it again.
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Old 05-26-2011, 10:28 PM   #6
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How thick is too thick for mortar bed in block foundation wall


The standard specification for concrete block regarding height is + or - 1/8" has been in existance for decades. It is far to loose and contractors usually like a block that is "a hair" less in case of bad mortar, sand or joint reinforcement, since the block are usually laid to an 8" module including masonry unit and mortar.

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Old 05-27-2011, 05:32 AM   #7
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How thick is too thick for mortar bed in block foundation wall


I've worked on quite a few sites over the years where the bed joints on blockwork or brickwork have been bumped up to 3/4 or 1 inch in the foundations to reach the required levels above ground, usually because the concrete levels were too low. If the beds were too big some slate might have been used.
Although technically the joints should be no bigger than 1/2 inch, I don't think any of these foundations have failed. I have seen brickwork on load bearing interior walls on 100 year old plus with big bed joints and there didn't seem to be any problems.

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