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Old 05-09-2009, 12:42 PM   #1
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cmu course layout???


I am building a small outdoor fireplace, and have a question about laying out the cmu courses. The dimensions of the fireplace are not divisible by 16", so how does one layout the courses and corners? Where should the cuts be located, etc?

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Old 05-09-2009, 12:55 PM   #2
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cmu course layout???


Is it divisable by 10, 12 or 14? They make 10", 12" and 14" blocks.

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Old 05-09-2009, 12:58 PM   #3
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cmu course layout???


No.

I already have 8" x 8" x 16" block. How does one build the corner leads in this case?

thanks
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Old 05-09-2009, 01:03 PM   #4
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cmu course layout???


Kinda depends on how far you are off a multiple of 16, how big it is, and in which directions, etc. If the balance and aesthetics are important to you.

There are all kinds of ways to make blockwork come out right, depending on your inventiveness.
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Old 05-09-2009, 01:09 PM   #5
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cmu course layout???


It is about 14" off. So, do I cut 7" pieces for each side, and make the appropriate cuts for the second course so all joints are centered? This seems like a lot of cuts. Is there an easier way? We are most likely going to stucco the fireplace, but I would like to learn how to do the layout correctly.

thanks
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Old 05-09-2009, 02:20 PM   #6
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It is about 14" off. So, do I cut 7" pieces for each side, and make the appropriate cuts for the second course so all joints are centered? This seems like a lot of cuts. Is there an easier way? We are most likely going to stucco the fireplace, but I would like to learn how to do the layout correctly.

thanks

It sounds like your only 2" short of bond. Either clip or saw 2" (right behind the first,end web likely) off 1 block per course & lay wherever you want. Just keep the piece in the same area all the way up. If you dont have something to saw the block with, a good 4" brickset chisel may be in order. Hopefully you have a few extra block though if your going to chisel, as they break somewhat easliy if your new to it.

Also, we always try to keep our pieces 11" or bigger. If you cant, & need smaller pieces, try to adjust so you can use both pieces, as in 1 sawing or chisel = 2 pieces, alot easier. Ideally, you want to keep at half bond, but you can stray 1" or 2" without problems. Good Luck!
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Old 05-09-2009, 02:51 PM   #7
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cmu course layout???


So, it sounds like it is not bad practice to make the cuts at only one corner and not the other (keep all cuts at one corner and fill the rest of the courses with full 8" x 8" x 16" cmu)...correct?

If the difference was something smaller...like 4", what does one do so the bond still looks good? Is there a general rule for dealing with these circumstances?

I have a diamond blade for my angle grinder. I would imagine that this would work for cutting the cmu.

As for reinforcement (vertical and horizontal), what do you recommend for a fireplace (about 7' tall) with a sitting area about 20" tall? Spacing of rebar and wire?

What should the distance be between grouted cells, etc?

thanks
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Old 05-09-2009, 03:59 PM   #8
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cmu course layout???


The use of reinforcement depends on the size, shape and height of the individual wall segments.

It is usually good practice to put a rebar and grout at every opening. A typical fireplace (even inside a house) may really not need any vertical reinforcement because it is such a robust structure with little ability to collect any load. The corners and relatively short horizontal dimensions give you something strong enough to resist a tank. If you were building a long straight wall 6' or more high out of 6" or 8" block you would typically put steel every 2'.

Often outdoor recreation items are not even covered by the IRC, but the west has a habit of prescriptively using reinforcement where it is not need and may be detremental.

It is always good practice to use horizontal joint reinforcement (Dur-O-Wal wire or similar) every 2 or 3 courses just for continuity, but it is not structural.

Dick
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Old 05-09-2009, 08:00 PM   #9
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cmu course layout???


Barbeques like yours are one of the reasons they make 14", 12" and 10" (sash) blocks.
They even make an 18" stretcher.
That would normally be 88" across there if just 16" blocks were used, by the way.
Well...... really it's mostly because of door and window locations and interlocking (perpendicular) interior wall connections.
Notice that each one of these walls is similarly done with five and one half blocks, but they range from 84" to 90".
NOTE: If you go buy some, the smaller blocks often come with only one cavity. That's normal. They're not selling you a reject or something.
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cmu course layout???-block-wall-14.jpg   cmu course layout???-block-wall-12.jpg   cmu course layout???-block-wall-18.jpg  
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Old 05-09-2009, 08:16 PM   #10
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cmu course layout???


Quote:
Originally Posted by figs View Post
So, it sounds like it is not bad practice to make the cuts at only one corner and not the other (keep all cuts at one corner and fill the rest of the courses with full 8" x 8" x 16" cmu)...correct?

If the difference was something smaller...like 4", what does one do so the bond still looks good? Is there a general rule for dealing with these circumstances?

I have a diamond blade for my angle grinder. I would imagine that this would work for cutting the cmu.

As for reinforcement (vertical and horizontal), what do you recommend for a fireplace (about 7' tall) with a sitting area about 20" tall? Spacing of rebar and wire?

What should the distance be between grouted cells, etc?

thanks
16" minus 4" equals 12".
You would use a 12" block if either you (or an inspector for your customer's bank, neighborhood association, etc) had a thing for only using full blocks.

And don't kid yourself that some of the high end communities don't get just that picky... and more.
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Old 05-09-2009, 10:48 PM   #11
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cmu course layout???


Quote:
Originally Posted by figs View Post
So, it sounds like it is not bad practice to make the cuts at only one corner and not the other (keep all cuts at one corner and fill the rest of the courses with full 8" x 8" x 16" cmu)...correct?

Correct, that is standard practice.

If the difference was something smaller...like 4", what does one do so the bond still looks good? Is there a general rule for dealing with these circumstances?

When your laying out the bond, flip one of the corner block the 8" way vs. the 16" way, for example. Worst case, put 2 clipped block in per course.

I have a diamond blade for my angle grinder. I would imagine that this would work for cutting the cmu.

Should work better than chiselling the block.

As for reinforcement (vertical and horizontal), what do you recommend for a fireplace (about 7' tall) with a sitting area about 20" tall? Spacing of rebar and wire?

I would tend to agree with Dick on this, Dura-Wall is cheap insurance, if you can buy it small quantity. As long as your setting the block on a good footing, vertical re-enforcement is probaly overkill, unless your going over 10 or 12 feet high.

What should the distance be between grouted cells, etc?

1 rodded pilaster in the center of the back wall, maximum.

thanks
Feel free to ask any more questions, I for one love building outside fireplaces!
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Old 05-10-2009, 08:36 PM   #12
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cmu course layout???


Maybe things in my area are a bit different. I have never seen a "factory" 14",12" or 10" long block. 18" yes they are used for certain layouts to avoid a 2" piece. Also the cuts are always in the corner. IMO a bricklayer that puts a piece in the middle of a wall is a hack. If you need to lose 2" then start out with a 14" cut. If you are building a corner the next course would be the head of the block going the other direction then the 14"piece. If it is a lead the the second course would start out with a 6" piece.
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Old 05-10-2009, 09:00 PM   #13
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cmu course layout???


Will the fireplace be surfaced with something or all of the walls (100%) exposed on both sides?

If you are building 8" thick walls (which is probably overkill), you are dealing with the wrong block supplier. In some areas, they use 6" partially reinforced block for 20 story loadbearing buildings.

For an 8" wall, a 12" long block (8x8x12) is actually a 12" 1/2 long block (12x8x8). If you need a 14" long 8" block (8x8x14), it is just a 1/2 length 14" unit (14x8x8).

If it is covered, there is nothing wrong with using split of sawed incremental units of standard 8x8x16 units. There are times when you have to cut units to fit a specific dimension that is designed.

I know of block producers that had 1200 different units in inventory, but still had to make special size units for a specific design - For colored architectural CMU masonry construction some block were sold at a loss since the price was only about $25+ per block if the quantity was sufficient. In some areas, inventory selections are minimal because of the local use of concrete masonry and only 8" block walls were common in comparison to other areas where 2", 3", 4", 6", 8", 10", 12", 14" and 16" thick block were made for walls. - the associated fittings (corners, bond beams, lintels, etc.) and fractional units were also available.

The block availability is a manufacturer and regional thing.

Dick
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Old 05-10-2009, 10:09 PM   #14
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cmu course layout???


Quote:
Originally Posted by NJ Brickie View Post
Maybe things in my area are a bit different. I have never seen a "factory" 14",12" or 10" long block. 18" yes they are used for certain layouts to avoid a 2" piece. Also the cuts are always in the corner. IMO a bricklayer that puts a piece in the middle of a wall is a hack. If you need to lose 2" then start out with a 14" cut. If you are building a corner the next course would be the head of the block going the other direction then the 14"piece. If it is a lead the the second course would start out with a 6" piece.
Stick around, Jersey, you might be surprised at what's out there in the world.

Here's a fun one for ya, using factory 12" blocks and partition blocks.
Attached Thumbnails
cmu course layout???-block-intetsection-1.jpg   cmu course layout???-block-intetsection-2.jpg   cmu course layout???-block-intetsection-3.jpg   cmu course layout???-block-intetsection-4.jpg   cmu course layout???-block-intetsection-5.jpg  

cmu course layout???-block-intetsection-6.jpg  
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Old 05-10-2009, 10:11 PM   #15
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The block availability is a manufacturer and regional thing.

Dick

It must be, obviously. From what I've heard Dick, Minnesota is one of the last areas that still see alot of block foundations, in new homes anyways. As a child, I remember hearing my Dad say block : poured was 90% : 10%. About 12-15 years ago, about 50/50. Now maybe 5% block foundations. As a matter of fact, just this spring, I heard from our large block supplier/manufacturer that they will soon stop making full 8" high block. We just completed a new block foundation, & it was obvious they're at least not spending any money on the molds. Kind of sad to see in some ways, but I'm sure it will be better for my body in the long run!

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