Building a foundation in stages?

[OlJarhead]

Here's a question for the pros:  what are the cons in building a SBC foundation (Surface Bonded Concrete) in stages?

My thought of late is that I want to try building an SBC foundation (poured footing, dry stacked cinder blocks, surface bonded and filled with concrete and rebar etc) under my cabin but want to do it in sections.  I was thinking that I could build the first 8 foot section and leave rebar sticking out of the two ends (one at 90% to the wall) so that I could attach new rebar to those and pour the next section later.

I could draw this (probably will) but wanted your thoughts on doing it like this.

Thanks!

[OlJarhead]

The shaded out area (lighter) is what I think will be left off in order to build the new section onto the first one later.

So the idea is that you build the footing with rebar sticking out, then dry stack the blocks so they work away from the area you want to complete and can be added to later, then bond the surface of the blocks and pour full of concrete leaving rebar sticking our where needed.

Come back later and start the next blocks and footing and work them together.

Might be too much to ask?  but it's what I'm hoping I can find a way to do.

[rick91351]

I don't know why you could not do such especially with the footing or footer depending where you all are from.  Once upon a time code was 30 times the diameter of the rebar was what a 'legal length' in a rebar joint.  So number 4 rebar would be a minimum of 15 inches   I would not make my cold joint straight as pictured but would taper it out in the form.

The rebar joint had to be tied with soft wire.  (Tie Wire in the hardware store)  The joint had to be wired at least three times equal distance apart.  Last footing I did or helped with we used those rebar twist ties and with the little twist tool with a handle WOW you could flat mend a lot of rebar in no time with those.  Back was hardly sore.  Hands actually worked the next day......

[rick91351]

I wish to add a disclaimer I know absolutely nothing about block foundations.  Footings for stem walls and block were both poured alike as far a setting and pouring minus the verts and the brackets we used to hold the stem wall forms.   

I have been around block foundations.  I have helped grout them but never helped with the construction nor know anything about block code.  That said having cold joints in blocks may be a absolute DO NOT DO!  I would not guess on spacing of VERTICALS AND HORIZONTAL rebar and size.  Might have to talk to a block layer or an engineer on that.....         

[archimedes]

I did a building that way.

You do have to mortar the first row of block to the footer though,  then dry stack above that.

I machine mixed the concrete for the footer,  so I did it in stages.   I used a piece of 2x wood with two holes drilled in it to block off the footer form (to keep the concrete from running out) but allowing the rebar to protrude.  I later put SBC over the cold joint (this may have been over kill).  I never had a problem with it afterward,  and I owned the property for another ten years. 

I am in FL.  So no frost heave and very well drained sandy soil.  Take if for what it's worth.

[Squirl]

Great idea.

The blocks will still be in running bond pattern which is one of the most important steps to locking the wall together.  A good layer of the SBC tying the two sections together should be just fine. Buttering the side of the blocks at the joint will help to make that section just slightly stronger than the other part of the wall.

Rebar is only required depending upon seismic location or eveness of backfill.  The general rule with 8" block is it is required if you are putting in over 5 ft of uneven backfill or in seismic category D or greater.  Other than that it is optional, but never a bad idea.  All the handy dandy charts you could ever want to read on rebar.
http://countryplans.com/smf/index.php?topic=12374.0

Technically speaking SBC walls have greater flex and tensile strength than traditionally mortared walls.  They have almost double the strength of holding sidewall pressure, but have about 33% less compressive strength.  The de-rated compressive strength isn't any major issue.  It is still rated at 400 psi which is more than enough for most three story houses.

The footing is a mild problem to overcome.  Rick mentioned about the cold joint.  The rebar and some concrete bonding adhesive should be able to overcome that.  CBA has some adhesive strengths greater than the strength of the concrete it is bonding.  It should be fine.

Technically speaking footings can be fully grouted masonry or crushed stone, a well adhered concrete joint shouldn't be the end of anything.  People make home additions all the time the same way.  I have been reading a lot of masonry books recently (almost a dozen).  Almost all simply state to drill a hole in the previous footing, epoxy in rebar, and just pour the new footing to the old.

From the code "Where minimum footing width is 12 inches, use of a single wythe of solid or fully grouted 12-inch nominal concrete masonry units is permitted."  If you just mortared 12" blocks, you would still be up to code standards.

Personally, I might want to get the footing out an extra half block so that you get an extra layer of block in running bond over the footing joints. It shouldn't be a major issue though.

[Squirl]

This is more of a personal ramble than probably answering your question.

So far, I have found masonry to be far more forgiving for the novice DIYer than any other medium of construction.  I don't lump concrete work into that. 

When I made a mistake cutting wood, that was another piece for the scrap pile.  If I did that on a 2x10, that was an expensive mistake.

If I made a mistake mortaring blocks, with a $10 cold chisel and a hammer, I could fix almost any mistake with only a few cents worth of mortar.  I also had a few hours to notice my mistakes before the mortar set hard and I could fix them without much trouble.

I didn't have to worry about shooting a nail through my hand.  I didn't have to worry about cutting off a finger.  I wasn't covered in itchy saw dust.  I didn't have to worry about falling off a roof. 

That's it.  Next time I'm building a house like Speedfunk and Drainl.

[OlJarhead]

Thanks Squirl!  I'm not exactly sure what you were saying about the footings though 

The blocks are 8x8x16 and I was planning a footing under them 8" deep and 16" wide.

[OlJarhead]

http://www.concretenetwork.com/concrete/footing_fundamentals/footing_dimensions.htm
Found that on footings.

Can't seem to find anything on the Load-Bearing Value of Soil in my area (which is a lot of rock -- some as big as a house) but I suspect it's pretty high.  Probably could get away with 12" footings in that case.

[OlJarhead]

http://www.concretenetwork.com/concrete/footing_fundamentals/why_soils_matter.htm

According to this I'm in the 5000 to 6000 Load-Bearing Pressure (pounds per square foot) category!  This suggests I could go as little as 6" wide but frankly I wouldn't want to and besides, it would be hard to put an 8" cinder block on a 6" footing! lol  But nice to know that I could do a 10" footing and be plenty strong.  Not sure that would be wide enough to work with though.

[OlJarhead]

This helps explain what an engineer said to me a year or so ago when I was working on plans for my root cellar.  He told me that in my soil he'd probably just go with an 8" deep footing for the walls based on the soil and the depth of the walls.  Though he also said, of course, that he was just guessing by looking at the soil.  My assumption is that he looked at the soil and went:  rock = strong.  but what do I know? lol

[Squirl]

Soils are slightly de-rated when it comes to design criteria. The concrete network stuff is more specific than the ICC.

TABLE R401.4.1 PRESUMPTIVE LOAD-BEARING VALUES OF FOUNDATION MATERIALSa
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_4_sec001.htm

I would guess normal design criteria would be 2000-3000 psi.

Not a big difference though.  You did conventional stick framing which is light frame design.
http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_4_sec003.htm

A lot of designs go with 16" because it accounts for the worst soils (clay).  12" is the minimum and will cover most buildings in most soils, but not all.

Most big box retailers only sell 8x8x16 but construction supply places will sell 12wx8hx16L. Technically for the footing, you could mortar 12" blocks together and fill them with grout without rebar and it would still evenly distribute the load of the house to the earth.  Rebar is so common, even when code doesn't require it, because the strength to cost ratio is so drastic.  Rebar is cheap.  $7 for a 20 ft #4 piece.  The strength and stability gain compared to the price is so drastic, people use it anyway.  I have spent a little time reading concrete engineering books and perusing code charts.  In almost every instance it is simply cheaper to add more rebar to concrete to gain strength rather than using more concrete.  Like adding rebar and keeping it a 6" concrete wall is cheaper than leaving it out and increasing the wall width to 8".  Block is a little different, but not much.

More is usually better, but at some point over designing can just be a waste of materials.  In remote locations, the costs of adding more materials may be different.

[kinshollow]

This is a really interesting idea for how to pour a concrete footing in stages. I have terrible soil and need a 21" wide footing, and thus had given up the idea of machine mixing the concrete myself as hopeless.

[JRR]

I believe my jurisdiction requires footings to be three times block-width .... 24" in your example.   But I remember re-bar overlaps only had to be 12 diameters.  Both details deserve further review with your local legal-heads.

[roadtripray]

I'm planning on using a cement block foundation, but I will be doing the traditional mortared block.  However I am interested in your approach to make sure I didn't miss considering something that I should have.  What are the advantages to doing it your way?  (bonded dry stack with grout and rebar)

And for those of you who have done something like this, how many block per hour/day, etc is a novice able to lay?  I know this will vary from person to person, but just trying to get an idea how intense of an endeavor this would be.

Thanks,
Ray

[OlJarhead]

I'm planning on using a cement block foundation, but I will be doing the traditional mortared block.  However I am interested in your approach to make sure I didn't miss considering something that I should have.  What are the advantages to doing it your way?  (bonded dry stack with grout and rebar)

And for those of you who have done something like this, how many block per hour/day, etc is a novice able to lay?  I know this will vary from person to person, but just trying to get an idea how intense of an endeavor this would be.

Thanks,
Ray

Stronger and easier to build

[Erin]

It is indeed easier to build! 
I dry stacked our basement almost entirely by myself (5'6" woman).  We also poured concrete into every 5-7 cores of the blocks, for additional strength.
In hindsight, we should have poured them, THEN surface bonded.  As it was, as the interior concrete cured, it moved the blocks just the tiniest hair, but enough to cause cracks in some spots that had to be patched.

[OlJarhead]

It is indeed easier to build! 
I dry stacked our basement almost entirely by myself (5'6" woman).  We also poured concrete into every 5-7 cores of the blocks, for additional strength.
In hindsight, we should have poured them, THEN surface bonded.  As it was, as the interior concrete cured, it moved the blocks just the tiniest hair, but enough to cause cracks in some spots that had to be patched.

A site I was reading about SBC showed pouring them first -- also seemed that they poured them all but I've read you can fill them with other things like dirt even though I'm uncertain if there are certain compositions that are best.  I believe it has more to do with insulation then strength because of the surface bonding.

[Erin]

The SBC is probably more than enough, but we decided to fill some cores for the same reason we built pilasters; better to overbuild than under. 

[roadtripray]

Is there a source that helps with estimating how much cement is needed for filling the blocks with grout with such a method?

Thanks,
Ray

[OlJarhead]

Here is a question:  I was unable to excavate close enough to the piers under my cabin in order to get the slab deep enough under the cabin in order to build the cinder block walls / foundation up directly under the walls where I wanted it to be so I got as close as I could (about 3-4 inches under the wall) and decided to take a different approach.  My approach (depending on feedback I get) will be to complete the cinder block wall to 8" above grade and then pour a footing beside the cinder block wall and tied into it.  My though was that the wall will carry some of the weight of the cabin at this point but the footing will also carry some.

I realize this is NOT ideal but in this location it's about all I can do.  The remainder of the footings I'll pour 16" x 8" centered under the wall such that a 'pony' wall can be constructed on top of the foundation to fit directly under the wall.


This was my original plan:  excavate the 'room' location for my composting toilet and batteries and then build the SBC cinder block walls up to 8" above grade and then a pony wall from there to the floor of the cabin -- this would allow me to easily match the wall to the cabin floor height above the foundation wall as well as allow me to pass sewage pipes etc through the wall and then insulate it.  I planned on 6" thick walls.

So, thoughts?  Am I crazy?  Would this work?  Should I pour the foundation on top of the SBC wall rather then beside it?

I'm also assuming that I'll need to tie the footing to the wall with rebar but beyond that am uncertain what should be done.

[OlJarhead]

Is there a source that helps with estimating how much cement is needed for filling the blocks with grout with such a method?

Thanks,
Ray

Not sure actually.

[Erin]

Is there a source that helps with estimating how much cement is needed for filling the blocks with grout with such a method?

Yep.

I always go Google for a calculator when I'm figuring this stuff.   I know I've seen one that calculates how much is needed by entering the height of the column needed to fill a core...  As well as one that calculates for an entire wall.