Dry Stacked CMU's

 
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Old 01-27-2005, 12:56 PM   #1
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Dry Stacked CMU's


I have heard that concrete blocks can be dry stacked and surface bonded, producing a masonry wall that is superior to conventional mortar method. I live in Florida on sandy soil. I plan on building a geodesic dome home on a garage/basement (very high ground, good drainage), some of which will be below grade, due to the slope of the land. I want to do most of the work on this project myself. I'm not very proficient at laying mortared block; but I've heard of this alternative. After dry stacking the block to desired height, the walls are coated with a figerglass-reinforced cement coating. My walls will be a little higher than a standard garage/basement, to acheive a 9.5 ft. garage door opening for a boat clearance. Has anyone here used this system, or is familiar with it? Also, I would like to cover the outside of the block walls with about 2" of sheet foam, but have been told that termites like to tunnel in it. Are there foam sheets that are made with borate additive for termite protection? Would this be adhered to the block, and then covered with some sort of stuccco...or maybe even the bonding cement for the blocks? Any help on this matter would very welcome. David
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Old 01-27-2005, 02:06 PM   #2
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Re: Dry Stacked CMU's


Drift,

WARNING AND I DO MEAN WARNING !!!!!!!!!

DO NOT DO THIS IN FLORIDA AT ALL !!!!

Surface bonding cement by Bonsai can be used with dry stack CMU's. You do not want to go over three feet in hight.

If you are not able to do mason work, Please hire a professional.

Teetor......... Did lots of work in Jax, Fla. Can you tell me where someone can build agarage in Florida that has good drainage. It has been a long time since I left, but for the life of me, I can't imagine a basement in FLA.

Just wondering if this is a fun post to see responses ??

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Old 01-27-2005, 05:24 PM   #3
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Re: Dry Stacked CMU's


No, Pond, this is not a fun post. There are a few high spots in Florida. I happen to own a piece of land that is about the highest elevation in Pinellas County. I can dig down 40' or so, before I hit water. And it is good drainage sand. I appreciate your warning about the dry stacked system not being used above three feet in height. Are you sure this is correct? I heard that, as long as you fill a certain amount of full-height cells with grout and rebar, as well as horizontal bonding (forget what the correct term is), it will work. I hope to hear from some viewers that have used this system for an 11 or 12 foot high wall, to see if it worked for them. 'Course, if others dispel this method as being unsafe, then I will have to learn how to lay block the old fashioned way. David
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Old 01-27-2005, 05:37 PM   #4
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Re: Dry Stacked CMU's


Pond, I know of some places on the Atlantic ridge where a basement could be built and there is another ridge that runs through the center of the state near SR 27, north of Lake Okeechobee where it might be feasible as well but those are the only places that come to mind.
I did run into a house with one in Hobe Sound just to the south of me. I have been wondering how they put it in and how the guy fared with the 40+ ins. of rain that we had in Sept. I wonder if the house popped like an empty swimming pool or just flooded. I know that he had to of been about 4 ft. below the watertable when it was built. Yankees!
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Old 01-27-2005, 05:52 PM   #5
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Re: Dry Stacked CMU's


Well, well, well, pondman, it appears that you had trouble reading the original post i.e. "(very high ground, good drainage)". And, Teetor disagreed with you....Hmm, are you going to start throwing insults at him now? I doubt you have the stones for it buddy!
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Old 01-27-2005, 08:22 PM   #6
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Re: Dry Stacked CMU's


Decks,

Go get you some possum, Granny is calling ya, your having a spell there. Can't you tell I read the post, but was asking about high ground in Fla?

I know, High ground and Fla, goes together like Brains and DecksEtc. It's a very rair copmbination.

Reread all my posts and you will see I have spared with Teetor.

Maybe those truck fumes do get to you though, riding on top in the chair and all.

By the way I'll give you 4 a side and still kick your A$$.

Tettor,

I knew it had to be a very limited area, and still wonder why anyone would do that with the water table the way it is. A good majority of my development funds were used to bring in good solid fill to make sites buildable. But to every 80 % of bad soil there is some 20% good I guess. I for one would love to see a dry stacked basment done up to 9 ft. high and parged with the Bonsal product and watch as the ground moves around it. I want all the sheetrock repairs. It would probably keep you busy for a lifetime, providing it stood that long.

Pond

Last edited by pondman; 01-27-2005 at 08:26 PM.
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Old 01-27-2005, 11:22 PM   #7
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Re: Dry Stacked CMU's


Say goodnight Ed.
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Old 01-31-2005, 04:22 PM   #8
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Re: Dry Stacked CMU's


Well, guys, I didn't intend to start a pi$$ing contest. I only wanted some helpful advice. I spoke to the building inspector for my city. He said he has seen where it was done around here, although not common. He, did say that, since it can't be inspected to make sure horizontal rebar was placed per requirement for block walls, that the engineer could possibly call for all the cells to be filled with concrete and rebar. You see, I can do that myself. And, as long as the cost of the additional rebar and grout, and of course the blocks, stayed considerably under what it would cost me to hire it done "professionally";well, I'd rather do it myself. Not only do I enjoy the satisfaction of building things myself, I also need to cut costs where I can. Obviously, there are areas where I will have to contract out.

I've talked to several who have used this method, and they said that it is a far superior method compared to mortared blocks. And if I fill it with concrete and rebar, I'll have a fortress foundation that will surely anchor my hurricane-resistant dome home against the big bad wolf.

I've included some quotes from some of my research:

"Applied 1/8" thick (minimum) to both sides, surface bonding cements have strengths that are superior to conventionally mortared block walls and they look a lot better too (no grout lines)! Grout between blocks is NOT an adhesive. Grout between mortarted blocks is a weakness - it is only done to keep a wall plumb and level. This easy to apply, water resistant, one coat structural stucco comes in tintable white or gray, making a finish coat or painting optional. It may help to think of surface bonding cement as a "fiberglass" reinforced coating. The surface bonding cement's polyester fibers interlock to form a VERY strong wall. Once your concrete block walls have been bonded, one hollow vertical core every four feet (or less, if specified by the engineer) is filled with ready-mix concrete and a #5 rebar for an exceptionally strong heat storage mass at a low cost. The economic strengths of dry laid block begin with the inherent properties of concrete block and the fact that block can be dry stacked 70% faster than laid in mortar. Surface bonded cement block walls have greater flexural and racking strengths than conventional mortar construction, too!"
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Old 01-31-2005, 06:28 PM   #9
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Re: Dry Stacked CMU's


DRIFT, the 2 things that I would look into are the surface bonding (peel strength) and tensile strength of the product. At 1/8" your tensile strength (in PSI) will be spread over 8". If you are going to pour the reinforced cavities as I would along with a topcap, I don't forsee any problems in your lifetime.
I could argue some points, especially the flexural and racking resistance but why bother? Without any comparison data the claims are sales propaganda.
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Old 01-31-2005, 06:48 PM   #10
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Re: Dry Stacked CMU's


Quote:
Originally Posted by Teetorbilt
Without any comparison data the claims are sales propaganda.
My thoughts exactly. I started looking around and found this http://mha-net.org/msb/docs/surfbond.PDF which seems to lend some credence to the claims of superiority over traditional mortar joints. Suffice it to say that drystack block filled with bar and concrete is little less than a concrete wall - far superior to masonry. I have to wonder why, given the apparent economic benefit, the 'surface bond' technique hasn't become more widely accepted. Hmmmmm? I have to admit I'm intrigued by the simplicity and potential benefits of the technique.

Last edited by PipeGuy; 01-31-2005 at 06:52 PM.
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Old 01-31-2005, 08:22 PM   #11
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Re: Dry Stacked CMU's


Essentially what you are looking at is 'stressed skin' construction.
After thinking this over a bit, the surface bond to the block becomes the weakest link. My second concern, and a major one, is the contact surface and cohesive ability of a mortar mix and the E-Glass. The E designates electrical and is a higher quality than S-glass although in this instance I see little difference between the two as one is still attempting to bond concrete to glass.
Racking and flex will be more controlled with the more cavities that are filled. A simultaneously poured topcap could reduce this by about 30% more, off the top of the head.
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Old 01-31-2005, 08:42 PM   #12
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Re: Dry Stacked CMU's


Quote:
Originally Posted by DRIFT-O-MATIC
I plan on building a geodesic dome home on a garage/basement (very high ground, good drainage), some of which will be below grade, due to the slope of the land. My walls will be a little higher than a standard garage/basement, to acheive a 9.5 ft. garage door opening for a boat clearance.
I'd look very closely at the loads posed by 9.5' of backfill against a wall - particularly if you have long spans of wall. It's hard to believe that 1/4" of reinforced parging (1/8" surface bond cement each side) is sufficient to resist the weight of a saturated backfill (hurricane conditions). Good luck. Please let us know how things proceed.
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Old 02-01-2005, 12:20 AM   #13
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Re: Dry Stacked CMU's


Pipeguy, the highest point that will reach the back-filled wall will be up to 6 feet level at the most. This will taper down to 0 at the other end of the dome basement, where the garage entrance will be. I intend to put closer to one fourth inch of parge (the recommendation was "at least one eigth of an inch") on each surface. Also each wall will be no more than 16' long. So, with concrete and rebar in each column, I doubt that there will be a problem with wall failure. 'Course, I'm not an engineer. That's why I'm going to consult one, before I proceed, after I get my plans from the architect. The only thing I'm not sure of, is will this still be cheaper than having a professional concrete fabricator construct the walls? I still have some homework to do.
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Old 02-01-2005, 01:01 AM   #14
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Re: Dry Stacked CMU's


DRIFT, It happens that I am an engineer. Without running numbers, your "basement" will exceed code anywhere in the state provided that each cavity is reinforced and poured. The coating will only be the icing on the cake, not to mention waterproofing,
Your architect should dwell on the compression strength of the block - mortar. Be forewarned, most officials look dimly on that which they don't understand. With a dome home built on a nuveau underpinning you can pretty much expect the worst from your local (hick) building dept.
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Old 02-01-2005, 09:21 AM   #15
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Re: Dry Stacked CMU's


Hey yal,
There are a few builders in my area that have used this system, however you say grouting. I say up north they use a 5 1/2 or 6 bag peastone mix with rebar. At least a ton or more of #4 or #5 reinforcing.
I tried this on a garage footing wall, that was only three to four courses and did not really care to do it again!
I started using ICF's about four years ago and love it! Anyone can do it with some research! If you have not tried, check into. It has many benifits such as heating, cooling, strength and finishing. Don't let the inital cost scare you off.
When you look at the time and additional cost to finish a CMU wall, the ICF's have so much more going for it! :Thumbs:
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Old 02-01-2005, 03:16 PM   #16
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Re: Dry Stacked CMU's


Quote:
Originally Posted by lpsonbuilders
I started using ICF's about four years ago and love it!
Now those things are THE BOMB! I watched a couple of local ICF (Insulated Concrete Form) houses go up a few years ago and even 'borrowed' a block to see what it looked like. I think that is a very good product. Polystyrene encapsulates a wire cage and each block interlocks with those around it. Cool stuff. Embedded steel strips provide "nailers" for drywall screws. IMHO, ICF is a far better product than surface bond cement.
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Old 02-01-2005, 10:32 PM   #17
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Re: Dry Stacked CMU's


I am looking into ICF very seriously, the local systems windload to 200 MPH. That is a VERY large improvement over the current code of 120.
I have been negotiating with a local distributor to build a one car, free-standing garage just to get my feet wet, everybody is going to bend a little to get the cost to standard block construction rates. If all goes well, I may enter the shell construction business.
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Old 02-07-2005, 09:25 PM   #18
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Re: Dry Stacked CMU's


I will consider the ICF's. It sure would be a lot easier on my back! I originally considered them. However, after listening to some arguments against them, I switched. The arguments from some of the dome kit manufacturers were that an uninsulated concrete wall would be a better thermal mass or heat/cold storage unit, much like a heatsink. I was told that if the inside of the wall were insulated, I would not receive the benefit of the thermal mass. Of course, these are peple who live in Wisconsin and other sub-zero lands. Their basements are completely buried below ground. More than half of mine will be exposed to the elements. So, maybe this would be the way to go. I would still get the strength of a concrete wall, and be insulated from the sun beating on it. Yeah, yeah, that's the ticket. How does the cost of doing the ICF wall compare to a conventional block or poured wall? Do you have any recommendations for manufacturers? The foam would have to have a borate additive; for the termites here in Florida will eat a dropped 2x4 before it takes a second bounce.
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Old 02-09-2005, 12:04 AM   #19
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Re: Dry Stacked CMU's


I've hung & finished a couple of ICFs here in Mo. One was covered with siding, stucco on the other, both came out very nice, although they did under engineer the floor joists and ended up with too much deflection for the tile work in the kitchen, so they switched it to laminate flooring. I know one of the home buyers & they are very happy with the decision to go that way after 2 yrs, low utilities and no worries when the hear the tornado sirens, steel framing used as well. :Thumbs:
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Old 02-12-2005, 09:02 AM   #20
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Re: Dry Stacked CMU's


The best thing about ICFs is that since the forms are left in place you'll never see the poor quality of the concrete. ICF contractors are often reluctant to vibrate the concrete because vibrators can destroy the forms. With a high wall especially, the various webs inside the ICFs contribute to aggregate segregation when concrete is dropped through them from the top. The lightness of the ICFs is a liability if it's windy out. If your excavation floods, the ICFs will float away. The forms have to be braced and aligned before the pour. It's tough to align the usually flexible ICFs. Every ICF wall I've seen has various bows and wobbles in it. You see them even in the promo shots on ICF websites. A fully grouted reinforced dry-stacked CMU wall is little different from a poured reinforced concrete wall. The advantage is you can do it yourself in manageable units. The surface bonding cement keeps the blocks in place until grouting and then is essentially irrelevant in a reinforced wall. After all, there are proprietary dry-stack blocks that interlock and use no bonding cement. Cleanouts are not required with dry-stacked CMU. The purpose of cleanouts is to let you remove mortar droppings from the bottom of the wall interior before you grout. No mortar, no cleanouts. If you're resonably careful with the block placement, you can build a virtually perfect wall. If you're thinking of using surface bonded dry-stacked walls without rebar and grout, note that the compressive strength of the wall will be about half that of mortared hollow CMU. The problem is that mortar not only binds the blocks together, it also separates them from each other. Without mortar, the coarse irregularities on the mating surfaces of dry-stacked blocks cause point loads that can crack the block if sufficiently stressed. Grouting the cores removes much of the compressive stress on the shells and alleviates the problem. You could also grind the mating surfaces smooth. but with the time invested you might as well mortar the blocks.

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