6 or 8 inch cmu's

by Jesse

I have a contractor that is building a house for me and he is using 6 in cmu's for the foundation (three high on a crawl space, little too no backfill against it). He stated these units have the same compressive strength as 8 in cmu's. I had an individual that used to be a brick layer tell me this was crazy. He said he had never seen a house built on a foundation using 6 in. Who is right?

Comments for 6 or 8 inch cmu's

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May 21, 2014
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starting a foundation NEW
by: Anonymous

if you are building a house 4 bed roomhouse which blocks inch is good for foundation (short) building

Apr 06, 2012
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6 or 8 inch cmu NEW
by: Charlie Cummins

Well Jess, it should of been 8 inch, but if the damage is done, hopefully your contractor did have vertical rebar every (at least 2 feet on center, a bond beam for the last course, with 2 number 4 or 5 rebar horzonal, and be sure he fills all the cells, (grout it solid) and make sure he uses 6 or 7 sack grout, OR DON'T PAY HIM.
If he does the above, it will hold anything you put on it. To learn more about building your own home, you should check out brickcertification.com, check all the links, and not have more problems like these.

Good Luck
Charlie Cummins

Jun 19, 2011
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Mason Contractor
by: Anonymous

I know you now know that 6" block is the wrong block for your foundation, unless you are building a shed. Most 6" block and 4" block are used for interior walls or exterior veneer walls. Depending on were you are located you have to use 8", 10", or 12" concrete block for a foundation. In the city I live in you don't have to use a bond beam on a house. You also don't have to fill it with re-bar or concrete on a house in this city, but it wouldn't hurt. I am a commercial contractor now all of those are required for the work I do. You have to fill it solid below grade and it has to be concrete block and concrete fill with re-bar every 2' to 4'. I hope this has been helpful to you on your project, also make sure they put a vapor barrier in under the slap good luck.

Jun 17, 2011
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12" block is the best for foundations.
by: Anonymous

First, I hope that the "contractor" was run off the job. If he was licensed, then I hope it was revoked.

Second, I hope there was a concrete footing.

Third, I would recommend using 12"x16"x8" blocks for the foundation. Make sure that the bondbeams (the channeled blocks that will hold the rebar) are up to code for your area. Then grout it solid (a special type of concrete that is used for filling the cells of the blocks (your local cement plant should know what it is)).

The 12" block grouted solid is the best way since it will have a larger base for your home to sit on. If done right, it will have an enormous amount of compresive strength and tensile strength (the rebar will enable to wall to be able to withstand more flexing and bending forces placed up it, such as during an earthquake>

By the way, I am a Journeyman bricklayer (International Union of Bricklayers and Allied Craftworker's Local #3 WA/ID/MT). The only time I have ever seen anyone using a 6" block as a type of foundation was for something non-structural (veneer work).

Oct 27, 2010
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Mason Contractor
by: Anonymous

Yes he is crazy the person told you correct I have been in the masonry business for 40 years I never heard of such. If he is using 6" block on your foundation run him off because he does not know what he doing. I could send one of my apprentices to do your foundation and they would know better, they may not know to use concrete but they would know not to use 6".

Sep 27, 2010
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6 in cmu for a foundation@#$%
by: Anonymous

That guy is out of his mind! Dont use 6 in cmu for a foundation! use 8 in cmu for a one story bilding and use 10 to 12 in cmu for 2 story and dont use lite weight they have to be concrete. and need to be grouted ever 2 feet with a bon beem on top. or every 4 feet vertical.

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