Hi, gang! I am drawing up some foundation plans, and have a question about the dimensioning of concrete block. A block is 8″ high. Do I add 1/4″ for mortar space? So, a 5-course wall of concrete block should be designed to be 41-1/4″ high?
Thanks for the help.
Tachi
tachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
Replies
No, a block is 7 5/8" high. Add the 3/8" mortar joint and you get 8" finished hieght for each course.
Length is 15 5/8" for the same reason.
Bowz
Aha! That makes sense. Thanks!
Tachitachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
No.
Block dimensions allow for the mortar joint. Draw 5 course wall @ 40".
Tachi, is block the norm for foundations in your area?
Are you planning to lay them yourself?
Someone who does foundation work can probably pour your stemwalls for less than you'll spend for block.
Joe H
Is there a superior walls distributer in your area?
Really? Poured is less costly than block? I am surprised, but will check into that, and thank you.
Tachitachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
Tachi, guess I should modify my statement.
A poured foundation might be cheaper.
Unfortunately I suspect you will be unable to find anyone to do it for you if your area is anything like here in Southern Utah.
You are owner builder designer? You're not dealing from a position of strength when it comes to hiring the concrete work.
Joe H
Yes, I am the owner/designer/builder, and I realize that could be a bit problematical. One advantage I have is that it is in a small town environment! (GRIN) Guess I will find out when the time comes.
Tachitachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
Depends. If you lay all the block yourself, then no. However, when I was getting all the design details together for my house, I would have saved 50-60% laying the block myself, but it would have taken me all summer long. I got prices on having block laid & having someone pour my basement. They ended up being about the same. Obviously, the materials are tons cheaper w/ block, but the labor was killer $$ wise.
Anyway, I ended up going w/ superior walls - since they come furred out, insulated & have a 15 year guarantee against water... It was a bit more, but I saved the price of water proofing - plus a bunch of time should I decide to finish.
Understand what you are saying. In my case, this 'block' wall is actually just a short wall to get below the frost line for the garage. It's a large garage, though. I don't think I would want to tackle it myself. I will have to deal with it when the time comes.tachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
Yes, I am the owner/designer/builder
Check this out with the building officials first. The way it works around here, you can get a permit as a HO for anything, including building a new house.
HOWEVER, when you look at the forms, there is a paragraph where you certify that you will perform ALL of the work yourself and not hire any of it done. So in effect it is impossible for the average HO to act as GC.
Local requirements may vary.
DG/Builder
Oh, boy. That's good to know. Thanks.
tachi
Family in Tucson, business in the Far East, and heart in the Colorado mountains!
There is an alternative construction technique with CMU called "dry stack". It does not use the mortar but rather stacks the CMUs dry and then coats them with a special coating that provides strength (the mortar doesn't actually provide much, if any, strength to a wall). There are a number of explainations of the process on the Internet. With dry stack, the length of a wall would be different than one using mortar between the blocks. One interesting, if very long, exposition on a DIY house project with dry stacked CMU is at:
http://www.texasmusicforge.com/gimmeshelter.html
I know I'm biased, but I'll explain something to the folks in non-seismic country. The mortar used in seismic zones 3-4 is at least type S - 1800 psi minimum and does add the the engineering value of block versus dry stacking them, of course. The proponents of the the plastered-on coating say it doesn't only because in the geographic area for which they write, block is rarely reinforced for residential applications. So, of course, a dry stacked but solidly grouted and reinforced CMU wall is stronger. DUH!
I been following the other web site too, on dry stacking. I have always been a believer of filling the cells with a pea gravel concrete mix.. So I thought I could add on to the shop with stack block. Ploblem would be filling an eight foot wall that is only just setting there.. BOB thinks I,m an idiot
Hey all:As the owner of the website with the "interesting and very long exposition" mentioned in this thread, I thought I might check in to answer any questions. The site CaseyR so graciously mentions contains a lot of info about dry stack block, but is intended to document the DIY house construction experience in all its grit and glory. I usually posted photos once a week to allow would-be DIY Demigods a chance to look over my shoulder and follow construction in more or less "real time."The old Dept. of the Interior manual on dry stack block is a bit outdated, but still the bible for dry stack block construction. It states that a properly constructed dry stack wall with surface bonding cement is six times stronger than a mortar and block wall. No mention of seismic zones in there, so I'll have to leave that to the experts.I *can* say that I've smacked my walls with a fork lift, accidentally dropped a huge dead oak tree on top of the house and regularly build trash fires up against the walls to shield them from wind - all of which is documented on the website - with no harm to the house other than a few scuff marks. That's a pretty emphatic endorsement of the structural integrity of a dry stack CMU house. The annual wildfires here and out west, coupled with my emergency response work in Mississippi immediately after Hurricane Katrina, make this type of construction look like a better and better decision.Best regards to all,Tio Ed
Austin, Texas
El Rey de Sweat Equity
Really enjoyed your website - as far as I got, anyway, which was about half way through. You mentioned on the part I read about using a fabric netting to reinforce the surface bonding cement. What additional info can you give me regarding materials used for such reinforcement. My impression was that you were using a stretchy material that would not seem to give a lot of additional strength.Thanks
There is a page on the site where I used a bag of the pre-mixed surface bonding cement on the walls as a test and was thoroughly unimpressed with the results. The nylon fibres tended to clump together giving me a bumpy look to the wall and the coverage was smaller than advertised on the bag. It occurred to me that the strain and stress relief for the concrete was only as good as the distribution of nylon fibres. In trying to find a good alternative source of nylon or polypropylene fibres, I stumbled across the nylon mesh netting sold in fabric stores.As documented on the web site, unrolling a section of this fabric and smoothing it on the walls got me a wonderfully even distribution of fibres and it tends to cling to the surface of a cement wall without any additional support. I troweled in a mix of 1 part Portland to 4 parts fine #4 sand by hand (using heavy rubber gloves) and got *much* better nylon fibre distribution and a smoother finish appearance at a significant savings over the bagged stuff. Again, as documented in photos on the website.As an experiment, The Wife scooped out a small bowl-shaped depression in one of our sand piles and began layering cement and nylon mesh and produced a bowl that we use for watering the dogs. It's watertight and certainly sturdy, so I feel safe in saying this technique has a lot more uses than just surface bonding cement.Nylon fibres in surface bonding cement are mainly there to reduce cracks during the curing process of thin cement layers, not for structural rigidity. There is a photo on the website of a handfull of the commercial nylon fibres used as an admixture by cement professionals. The stuff's not a whit different from the nylon used in the nylon mesh used in a typical bride's veil. The Romans (history's master engineers) used chopped-up horse tail hairs in their cement to do the same thing we use nylon fibres for and their structures lasted for centuries. You can buy bolts of this nylon mesh net fabric for around $27 USD at Wal-Mart fabric departments. Be prepared for some funny looks, a few questions about your wedding plans and/or sexual preferences when you buy the stuff...Best regards,Tio Ed
El Rey de Sweat Equity
Edited 3/26/2006 9:26 am ET by Tio Ed
Are you sure you're reading that correctly? They had those same paragraphs when I applied for my permit, but you had to sign them specifically.
I had to sign a line that said I would oversee all construction & one that said I would perform all electrical & plumbing work.
If I DIDN'T sign those paragraphs, I would have to provide license #'s for my electrical, plumbing & framing contractors. The main reason for those paragraphs is so that a person acting as his own GC doesn't just grab joe schmoe off the street who will wire his house.
Yes I am sure. Repairs are one thing. They don't want some yahoo to play GC without a license by building spec houses one at a time under the guise of building "his own house".
DG/Builder
Our state requires that you can only build 1 house every 5 years w/o a license.