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Older 8" CMU Block Actual Size

Older 8" CMU Block Actual Size

Older 8" CMU Block Actual Size

Hello, I have a 1967 CMU building and found the exterior wall block dimensions are actually 8"D x 7 5/8"H x 15 5/8"L as opposed to the standard 7 5/8"D x 7 5/8"H x 15 5/8"L. If a modern standard block is used to fill in some of the window openings there would be a 3/8" lip if the blocks are placed flush with the exterior walls. Is that common to find with older buildings and are custom depth CMUs then specified?

I am working with a very busy SE on adding some courses to the exterior walls and filling in some windows, etc. We just finished the interior demolition to expose the walls and ceiling, etc, and the SE will be back out soon to review everything and give direction. I find CMU construction quite fascinating so I figured I'd ask about the size difference before the review.

Thanks! - Jeff

RE: Older 8" CMU Block Actual Size

For looks, the new blocks will not match the pattern of the original blocks at each window, unless covered by a stucco-like mix. Filled in windows in old buildings always seem to stick out like that, regardless of where the blocks or bricks are placed.

So the difference in "depth" could be inside or outside to either make the filled-window a "feature" with a reveal around the old opening, or flush to make the outside smooth with the new stucco/wall covering.

RE: Older 8" CMU Block Actual Size

Fill the opening with 2 – 4” wythes of conc. blk. in the same running bond (whatever bond) pattern to match the existing, and match the inner and outer plane surfaces of the wall. Fill the collar joint with mortar or grout, and put in some metal ties btwn. the wythes. You could use a current std. 8” conc. blk. and fill the inner 3/8” void with sheet rock if your interior finish allows. There are a number of ways to skin this cat. The face shells of the new and old conc. blk. will always look differently due to age and weathering, and need some attention to minimize this difference if that is really important. In fact, current loads of conc. blk. from different suppliers will look slightly different due to ingredient and manufacturing differences. RE: the 8” thickness vs. 7&5/8”…., many conc. blk. manufacturers have some slightly different special blk. sizes.

RE: Older 8" CMU Block Actual Size

Yeah, I certainly see the old bricked up windows that are slightly inset on older buildings. That looks great to me. Looks don't matter much since it will have new interior walls covering up this work and the outside doesn't need to be fancy. Sounds like there is not a structural issue with the slightly narrower blocks as I somewhat suspected. If needed, the two layers of 4" blocks with ties and grout between is a great way to meet the old thickness perfectly. I'll see what some local block suppliers have available too.

It is indeed running bond, the adjacent half blocks would get knocked out to allow a complete tie in with the new work and horizontal reinforcement can be added at that point if needed. At least the walls are in great shape, minor step cracking in a few spots and one window has a steel lintel that swelled way up over the years and lifted one side of the wall above it by about 1/2 inch. It will be interesting to see that particular window blocked in and the lintel replaced. I would think the wall would come back down to its original position, allowing the head and bed joints to be knocked out a few at a time and repointed.

I am expecting the SE to be adding vertical reinforcements with grout to the walls to allow us to go up more courses, the walls are at about 14 feet right now. It will also be interesting to see what is under the parapet wall roof caps. I would think we will find a bond beam but I don't really know much about this stuff so I'm on a bit of a journey and having fun seeing what the SE comes up with. Thanks for the input! -Jeff

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