Replies

1. 
   Tomrocks21212 | Jul 04, 2008 05:41am | #1

   A lot depends on your soil conditions. I did a lot of building in Maryland, in areas with a lot of micacious red clay, and an unfilled 12" block wall was only good for about 7' of unbalanced fill.

   I built a small commercial building where all the 12" block was to be filled, and even with vibrating the rebar, I'm not convinced that all the cells were filled top to bottom, due to misalignment of the webs, excess mortar blocking the concrete, etc. Yes, we pumped it, with aggregate no larger than 3/8".

   I can't imagine that you'd get great results filling 8" block. I'd go with 12. And I'd fill every cell. And drill witness holes at the bottom so you can make sure the 'crete gets all the way down.

   HOWEVER...... There are certain blocks designed to be filled. In the Mid-Atlantic region, they were called "Ivany block". Various widths were available there, I think 8, 10, 12, 16, and maybe thicker.

   I wish they'd been around when I did that job, I'd have had more confidence with them.

1. 
   JohnFinn | Jul 07, 2008 10:14pm | #15

   What is the span of your longest wall?

   edit: to malibuds3

    

   Edited 7/7/2008 3:16 pm ET by JohnFinn

1. 
   malibuds3 | Jul 08, 2008 02:13am | #16

   It is basically a 50' x 30 box w/ some bump outs kind like a T shaped 2 stories. on the top of the T I will have 12" (the most back fill) it goes down to day light at the bottom of the T. #5 with rebar every 4'. a 4" perforated PVC pipe for drain and rub-R- wall waterproof. vent for radon with PVC and have gravel over a 20 mil liner no slab now. trying to watch cost.
   Thanks fellas

1. 
   JohnFinn | Jul 08, 2008 02:41am | #17

   I would steer towards the 12" block, although 10's are popular in our area too. May want to consider pilasters on at least the 50' wall as others mentioned, and if you can located beams at pilasters all the better.

2. 
   frammer52 | Jul 04, 2008 05:18pm | #2

   What do your plans specify?

1. 
   malibuds3 | Jul 04, 2008 10:23pm | #5

   The plans are for a crawl space but elevation gives me a basement. 12" is about 2-3 grand more. i think I may use 12" on the wall that has the most fill. the rest of the walls will get 8", they get less fill. thanks for the help .

1. 
   Matt | Jul 05, 2008 01:40am | #6

   Look at your code book.   I'd have to doubt that 8" block would support 8' of unbalanced fill.  

   Sounds like you have the right idea though...

   Do you really want a basement under the entire house?  How about a 1/2 or 1/3rd basement with step down footings in the area where you were planning to do the 8' of digging?  Block basements aren't my favorite...

   BTW - where do you live - ie: what is the minimum required footing depth.

1. 
   malibuds3 | Jul 05, 2008 04:48am | #7

   it is 8" (footer) and 18" down. the basement is already dug. I look into superior walls but I don't need a slab floor right now how does poured walls compare w/ block or filled block? superior was about 100$ a foot for 8' 2"

1. 
   Matt | Jul 05, 2008 02:37pm | #8

   Poured walls should be somewhat cheaper than precast but more expensive than the block walls. 

   Sounds like the wheel is already in motion and I wouldn't want to get in the way of that...

   One thing though - the basement slab helps stabilize the basement walls to prevent them from being pushed in by the backfill.   You might want to double up on the rebar sticking out of the footers, even if the extra doesn't go all the way up the wall.

   Also, for any long walls it is always good practice to add a pilaster or 2.

2. 
   john_carroll | Jul 05, 2008 07:47pm | #9

   Reinforced block walls can be very strong and are used for prisons and in seismic zones. But they have to be detailed correctly to work optimally. Here are three major concerns:

   1.) The steel needs to come up in the center of the core. This requires careful layout when you do the footings. Also, there are wire brackets to keep the steel centered as the block wall is built.

   2.) The grout needs to be specified for the job. Technically, grout and concrete are two different products--although they are often made up of the same materials. Grout must have a lot of slump to fill the spaces. It must have the proper size aggregate to ensure that it flows into every corner of the space. It needs to be richer in Portland cement than most concrete mixes because the goal is a tenacious bond between the steel, the grout and the inside surface of the block. In commercial work, the make-up of the grout, including the proportion of Portland to aggregate, the slump, and the maximum size of aggregate are typically specified.

   3.) The top of the footing where the steel emerges must be kept clean. In commercial work, cleanouts are cut into the first course of block so that mortar droppings can be cleaned up every day as the wall is laid up. After the wall is finished, these lookouts are patched prior to pouring the grout.

    

3. 
   Jim_Allen | Jul 07, 2008 05:27am | #13

   Good info there Mudslinger! Why dont' they grout early on during the wall building? Bob's next test date: 12/10/07

4. 
   john_carroll | Jul 07, 2008 06:37pm | #14

   Why dont' they grout early on during the wall building?

   I think it's because you'd end up with cold joints that would weaken the system. The blocks alone almost always have more than enough compressive strength. The steel and grout are added to provide tensile strength to resist the lateral forces imposed by the soil.

   I've scanned a page from Christine Beall's "Masonry Design and Detailing." If it comes through, check out the little drawing at the bottom of the page comparing the slump needed for masonry grout.

   
5. 
   Jim_Allen | Jul 08, 2008 02:56am | #18

   That came through fine...Thanks Mudslinger. Bob's next test date: 12/10/07

3. 
   Danno | Jul 04, 2008 05:47pm | #3

   You don't need a brick ledge do you?--when I was in drafting class, that's when we drew plans with 12" block--or in a foundation wall for a garage where the floor edge would rest on the block, IIRC. (It makes sense to me that 12" block would betetr resist inward pressure, but if you have proper drainage and backfill, there shouldn't be a lot of that.)

4. 
   mike4244 | Jul 04, 2008 10:07pm | #4

   I would use 12" block, vertical and horizontal reinforcement. Fill the block every two courses so you are assured of no voids.

   mike

5. 
   Henley | Jul 06, 2008 03:58pm | #10

   Just thought I'd point out the
   obvious-

   Those twelves are heavy! My back doesn't like them.

1. 
   malibuds3 | Jul 06, 2008 07:22pm | #11

   thanks for all the help, I hope my mason is strong "lights" cost a dime more. I think i am going to stick w/ 12" for the wall w/ the most fill and 8" w/ the others and reinforce the 12s every 4' and the 8" every 2'
   thanks again it has been a big help .

6. 
   Jeff_Clarke | Jul 07, 2008 05:19am | #12

   We use a lot of 10" cmu for this application.

   Jeff

7. 
   Nails | Jul 08, 2008 04:32am | #19

   Malibuds3.........Times they have changed....in 1972 I built 2 two story house's on 6in block and was passed by local codes. There was no rebar in it and the blocks were filled with vermiculite. Back fill was done after shingles were on and water proofing and drain tile. I occaisonally pass by these homes and have talked to the current owners they have never had any problems nor those before them.

   I'm not trying to make any point, just passing along some of my past experiences.My thoughts are for you to do what ever makes you comfortable ,no cost is to much to have that feeling.