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Surface bonded CMU's

Chris_River's picture

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We are trying to build a 9' cmu wall to support a concrete deck that will be 10' deep and 56 feet wide. There is already a solid footer in place. I have heard that surface bonded block walls are strong, relatively easy to build, and lend themselves to sporadic work times. If anyone can give us any tips, comments, or suggestions on how this works, we would greatly appreciate it. We also need the names of suppliers or companies to either use or avoid. We are located in eastern PA. Thank you for any help you can give us.

(post #171449, reply #3 of 15)

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Thnks Matt, I appreciate the comments. Yes, it's quite a wall and because we can only work on it evenings and weekends, we were trying to avoid the issue of mixing small batches of mortar in building it the more traditional way. There's no water at the site as yet, which complicates it too. Since we aren't concerned about insulation, and the area will have a stone floor, we really just need the strength to hold up the floor. That will be done with a pan, I presume - that part isn't my problem! (Yes, I know it will determine how the top of the wall is built.) Thanks for the link, at least it's a start!

(post #171449, reply #4 of 15)

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Chris, I looked into surface bonded cmu's two years ago when I decided to build a house for my family. There are several companies available but a major player is Bon-sal. They make a product called Surewall that is applied by trowel or sprayer in 1/8" layers. Their spec sheet claims if applied properly it has 5 times the lateral strength of mortared walls. Remember, the mortar used between blocks is not there for strength but primarily to level the blocks. The strength comes from the rebar and mortar used to fill the cells. Further, Bon-sal does not recommend you use their product in conjunction with a mortared wall - dry stack only. Oh yeah, after looking into all this we went with poured concrete walls - the surest bet you will get a strong finished product. Research well and good luck.

(post #171449, reply #6 of 15)

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Chris: I'm currently building a basement under my existing house (evenings and weekends) using 12" CMUs dry stacked and surface bonded on both sides. Last summer I completed two 30' walls and they wintered very well (I'm in Minnesota). While Surewall is probably most common, I'm using a product out of Canada that I purchase at Menard's. Sorry, I don't have the name in front of me. One thing you may consider, each time you mix a new bag of the stuff, it will be a slightly different color and you'll have a joint between each batch. G Sam is right in that most the strength of any masonry wall comes from the rebar and grout put in the cores. Surface bonding is much stronger than mortar.

Is this wall going to be retaining soil on one side of it? If it is, then you should consult an engineer regardless of the type of wall you're going to build to make sure it is designed to resist the loads placed on it.

Let me know if I can give you any other info.

Jim

(post #171449, reply #8 of 15)

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Hey, this is really interesting, and I do appreciate all the comments. The comments about the strength of mortar seem to match what we have learned in classes and reading - which is one of the reasons we were pursuing the surface bonded approach. We discovered Quikrete (sp?) makes something called Quikwall. Those folks are so very nice and helpful, AND their product is availble locally, which helps. We also have contacted Bonsal with Surewall-they haven't been quite as, shall we say, responsive to questions. One side of the wall will have soil (with a liberal stone layer immediately against it-want to control hydrostatic pressure since the soil has a lot of clay in it) and the other side will be open for a storage area.

(post #171449, reply #9 of 15)

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Chris:

Let's see if I got this right:

~ 76' of wall 9' high

9' of unbalanced fill!

No water on site!

Sounds like your going to need to fill the block solid with grout, and install some rebar in the webs. Maybe need 12" block. Next, you're gonna tell us that you plan to do all the mixing (including the grout) by hand, backfill by hand, and that you are going to haul all the materials to the site your self! I hope you are about 29 years old, don't have a regular job, have 3 hardworking teenage sons between the ages of 16 and 20 with nothing else to do, and know someone with a water truck that you can borrow.

Hire a masonry crew for $1.25 - $1.75 a block. Extra for the grout. This is really not a DIY project. Otherwise you are going to be on the 5-yr. plan, and you will be trading your time at about $4 an hr!

Or, why not build a wood deck? With the height of that thing, that is really what's indicated.

(post #171449, reply #14 of 15)

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We are trying to build a 9' cmu wall to support a concrete deck that will be 10' deep and 56 feet wide. There is already a solid footer in place. I have heard that surface bonded block walls are strong, relatively easy to build, and lend themselves to sporadic work times. If anyone can give us any tips, comments, or suggestions on how this works, we would greatly appreciate it. We also need the names of suppliers or companies to either use or avoid. We are located in eastern PA. Thank you for any help you can give us.

(post #171449, reply #1 of 15)

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That's quite a wall - sounds like it's 1000 blocks - give or take. Will it be filled before the concrete is poured or will you be pouring on top of corrugated metal?

Surface bonded CMU's - hmm…. I've used surface bonding cement for parge. Works great for that. Doesn't crack - it's got fiber in it. But never used it for what you are proposing. I know the manufactures say it will work to set block dry - but I'm skeptical. Especially for a project of your size. Besides, I think that you may find that the price of the surface bonding cement may approach the cost of a mason - or, sounds like you need to learn to lay block.

Here is a link for you. If you look at the bottom of the PDF doc, you will see that they offer some type in installation booklet.

(post #171449, reply #2 of 15)

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Have you considered Insulating concrete forms. Some systems lend themselves well to striping the foam after the pour. Another option would be to stucco over the foam.

(post #171449, reply #5 of 15)

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G Sam:

Above you said:

>"Remember, the mortar used between blocks is not there for strength but primarily to
level the blocks. The strength comes from the rebar and mortar used to fill the cells. "

Wow, that's Interesting. Care to expand on or corroborate that statement?

(post #171449, reply #7 of 15)

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Matt G.

That's the way I learned it, too , at least regards laterall forces against the side of the wall. Mortar in traditionally laid block has relatively little adhesive strength to resist separation of the block as lateral forces push agaist it. The parging, with fiberglas(?) strands in it provides a "skin" which supposedly holds the block together better against such forces.

I believe the process is also called "block n bond" and was developed for low cost, non-skilled housing/construction.

The one project I worked on, years ago, had a "downfall:" The manufacturer recommended mortar evry 5 or 6 courses or so, to reachieve a level top, the parging was weak across the mortared line, and showed some surface cracking, FWIW.

(post #171449, reply #10 of 15)

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Wow, that was kinda rough. On the other hand, I'm starting to see a disturbing trend around here - 9' high patios and 9" high decks??? What gives?

(post #171449, reply #11 of 15)

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Matt G,

I built my garage foundation walls out of concrete block stacked dry and the walls "B-Bonded". Before I attempted this, I consulted with my concrete/brick supplier (he has been in the business over 40 years) and he told me the same thing; that the primary uses of mortar was as a leveler, and it gives little or no lateral support. He told me the block "B-Bonded" on both wall faces would be much stronger than a normal mortared block wall.

I used corrugated brick ties as shims where needed to level the dry block. All the block were stacked dry and tight (butted tight...no gaps) so that the fiber glass would bond well. Putting mortar between rows (as mentioned by Bob Walker) creates too large of a span for the short fiberglass "hairs" to bridge across, thereby causing the joint to fail. The chopped up fiberglass mesh is only about 1/2 inch in length and can therefore not bridge gaps wider than this and hold its strength. That is the reason the block must be stacked tightly together.

The only row of block that gets mortared, is the bottom row, so that the block wall can adhere to its base.

Instead of mortaring the bottom row, a suitable construction adhesive also can be used to bond the block to its base. I went this (adhesive) route.

My wall was only 3 rows high (remainder of wall was wood frame) but has continued to hold very well. No cracks or deformities. My garage is 5 years old.

Friends of mine said they used this technique in the coal mines. Claimed it worked well and was very strong. Said you could not break the standing wall with a swinging sledge-hammer. They claim to have tested walls this way. I always thought about building me a "practice wall" and trying this sledge-hammer routine; but never got around to it.

B-Bond is also waterproof.

An excellent article on this subject was written by Paul Hanke; titled SURFACE - BONDED BLOCK. This article can be found in the book Foundations And Masonry, published by Fine Homebuilding.

Davo.

(post #171449, reply #12 of 15)

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Daveo:

Again, 9' high patios and 9" high decks - waz-zup with that?

(post #171449, reply #13 of 15)

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Matt,

I didn't say I would build a 9 foot wall out of B-Bonded brick to hold up a 9 inch thick patio. I simply was answering your question about mortar and racking strength.

I personally prefer using concrete with rebar added.

According to what I have researched, the B-Bonded block wall could possibly work, but the wall would have to contain at least 4 pilasters; each filled with rebar and concrete to the top. These pilasters would have to be tied into the main wall by setting every other course of the pilaster in a perpendicular fashion to the main wall itself. All cavities in this pilaster must be filled with concrete. There would have to be a pilaster built at each end of the wall and at the middle of the 9 foot span.

Would this wall suffice in supporting what needs to be supported? I honestly don't know. Nor am I qualified to say. Only a structural engineer could give this answer.

Davo.

(post #171449, reply #15 of 15)

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I can't tell you how many CMU "retaining" walls I have seen fallen over from the pressure of the earth. I really think you should reconsider an alternative. I really can not see a surface bonded wall having much retaining stength. THis wall should either be cast or laid of interlocking block made for this purpose. A block or wood wall should be tied into the earth which it is supporting.

Pete