Poured Foundation in parts.

Squirl · July 14, 2011, 11:58:16 AM

So I am leaning toward a poured solid foundation in pieces. Here is the plan for critique. I have run into a few snags. I have been not been able to find a single rental organization that will rent concrete forms. So I would have to build them. This would not only be a massive cost, but a massive waste of material. My estimates for 3/4" plywood at $20 a sheet for 1200 square feet is $800. My estimate for the fasteners for this are $6 per linear foot for 100 linear feet or $600. So around $1400 in forms. My estimate of concrete is 10 yards at $100 per yard or $1000. For a total of around $2400 for this option. What irks me most is the massive waste of the plywood.

My current plan is to pour it by hand. (I am well aware this is a lot of work) I was hoping to build two 8' wide x6' tall forms for a total of around $120 on the forms. I would hold the forms in place with 2x4's in a triangle with soil pins in the bases. I would use 2-2x4s with a hole cut out for the horizontal rebar on the edge clamped together pipe clamps. I assume they would hold the weight of the concrete based on the rate of pour. Because it will take me time to mix and pour from the bottom to top, the bottom will begin to harden as I get higher, taking the pressure and weight off the form. The rate of pour will be fast enough though that there will still be a wet bond between the concrete. Similar to the concept of slip form concrete pouring, only without moving the form.
I would leave a keyway on each side and use concrete bonding adhesive between the concrete panels. Like this: http://www.quikrete.com/ProductLines/ConcreteBondingAdhesive.asp It is listed with a shear strength of 1250 PSI. Since concrete has a compressive strength of 2500 psi and its tensile strength is rated at a small portion of that, I thought that this would be stronger than the concrete is normally for sideways force. It shouldn't have almost any sideways force anyway since there will be a maximum of 1 ft of unbalanced backfill. The cost of this would be 10 yards of concrete at a 6 bag mix or 60 sacks at $10 a sack or $600. Sand and Stone are a fixed price of $300 a load of 12 yards delivered, or an additional $600. I would have lots of each left over for projects. So a total of around $1400. Can anyone see any problems or code violations with this other than the massive amount of time and labor? At $1000 after tax difference in cost time starts to stop being money and money becomes money.

Alan Gage · July 14, 2011, 04:38:24 PM

Have you priced having a crew come in, set up the forms, and do the pour? It's nice doing things yourself but maybe the cost wouldn't be so bad since their forms will be reusable. They might be in and out in just a couple days.

I've never worked with concrete before and considered mixing it by hand and pouring my own for footings but in the end formed them up myself (only 8"x16") and had someone who knew what they were doing help with the pour. I also had them lay 2 courses of block and then do the slab pour once I placed all the foam.

It was a little more than I wanted to spend but I'm very happy I did it that way. With them knowing what they were doing things went fast and smooth and I couldn't be happier with the results. It ended up costing me $3000 in labor, which was more than I anticipated, but it probably would have taken me an extra 3 weeks to do it by myself and lots of headaches. Now that concrete is done I'm moving along with framing it myself, which I find much more enjoyable.

Good luck,

Alan

July 14, 2011, 05:26:45 PM

I would certainly get a bid from a couple guys.

Having been around concrete for several years. (Drove ready mix truck) Seen a lot of stuff and I was always helping the contractors and DO IT YOURSELFERS. One thing to keep in mind your mistakes and boo boo's are now set in stone.

archimedes · July 14, 2011, 05:29:30 PM

I recently got a price for a 20 X 30 basement, 8' walls. It included excavation, forming, concrete, rebar, 4" basement slab, waterproofing and backfilling - $10,000.

Squirl · July 14, 2011, 05:43:11 PM

I have done a little concrete work, but never a full foundation myself. Part of the reason for doing it is the experience. Thank you for the suggestions, but I will be attempting it myself. $10,000 would be a half of the price of the entire house. Does anyone see any problems with mixing and pouring it in small 4-8 ft increments? A post and pier foundation is not even on a full perimeter connected footing and is not connected. I figured this would be better for stability, chance of shifting, or chance of sinking.

July 14, 2011, 06:01:10 PM

I'm not sure I understand why you abandoned the block foundation idea. I think that would be easier for a DIY.

I built a small cottage on a crawl. I dug and formed the footer myself. Put the rebar in myself. Mixed the concrete myself with a rented mixer. Then layed three courses of block. I was a lot of work but not technically challenging. Plus it was the first time I had ever done concrete work.

Squirl · July 14, 2011, 08:10:13 PM

I didn't abandon it. Block would just take more time, labor, and money. I also think this would be stronger. I started two threads to explore the concerns and procedure for each method. I would still have to mix yards of concrete. I would have to set, measure, cut the blocks to fit. So, in my original estimates, it would take just as much rebar, almost as much concrete, the block, more cutting and fitting. So far this option is in the lead. I also have some experience pouring concrete and none with block. If I am correct in my current explorations of drystack not needing the added work, time, and materials of the rebar infill. It would catapult block into the lead.

I've explored and abandoned all other methods.

Don_P · July 14, 2011, 09:25:33 PM

I poured the lower part of my shop walls somewhat similarly. On 3 sides in the rear I wanted a 5' tall poured wall as it was cut into the bank. I made a set of slipforms about 10'x 2' tall out of boards and wired them together. I poured a 1' bond beam to cap it. I hand mixed and used as many of our many rocks as could be put into a fairly wet mix. I made extensive use of an old sawzall without a blade. The nosepiece will sink a rock or vibrate the form. I built the wall 12" thick and under a residence that would probably need to be 16" thick if they're sticklers.

I don't have a problem with your proposed wall, Superior precast walls come in panels that are glued together... the sill is bolted every 2' and the floor diaphragm is well connected to the sill (their install guide is a free download).

UK4X4 · July 14, 2011, 10:34:15 PM

"I recently got a price for a 20 X 30 basement, 8' walls. It included excavation, forming, concrete, rebar, 4" basement slab, waterproofing and backfilling - $10,000. "

Daaam your obviously not in Colorado my quote was 26K for a 48X32 above ground with footings

Presently I've concidered a prefab sat on drained gravel- 1 day install but 24K for just the prefab walls

I've been wondering about making my own plywood molds and doing them on the ground and then place each one seperately

Thats all the prefab guy is doing !

July 15, 2011, 06:10:32 AM

Thanks don_p. I was looking to make sure my math and assumptions on the rebar and concrete bonding adhesive were accurate. Or if I was missing anything, because I had never done a pour in multiple parts. More sill bolts is an excellent idea.

UK4X4

If you are building your own forms you can find all those fast forming clips the contractors use here:
http://www.awardmetals.com/product_rapiform.htm
http://www.dhcsupplies.com/concrete/conmiscellaneous.htm

I like the first link because it shows all the specifications of how to use their products to build a concrete form, such as spacing and load calculations.

JRR · July 15, 2011, 10:57:34 AM

I have done a little of all of it ... concrete by hand, by ready-mix, block, stone, ... but so "little" that I'm no expert in any. I understand the need to do-it-yourself. Some times it's money, or site access ... or just a "need". I would recommend the footing to always be done by ready mix delivery. I have done them singlehandedly ... it just takes preparation. Proper depth and width of the hole ... cleanliness, virgin soil, no organic inclusions, reinforcement, etc, etc. Good weather. I like to have an abundance of rebar in the footing and a number of rebar pieces stuck vetically in the wet concrete along the center of the planned wall location. If using block for the walls, some of these vertical re-bar pieces may not fall in exactly a useable location ... just ziz-wheel them off!

Block wall construction is certainly the easiest for me. I like to use regular mortar lay-up and finish the surface with surface bonding cement. I just find using mortar faster for me than dry stacking ... and the block spacing is "standard". Extra steel reinforcing can be included in horizontal joints and vertical cores as needed.

Your plan for DIY concrete forms may be just fine, but I would recommend using more simple vertical slip forms. Much cheaper and simpler forms. Decking wood works just fine. Almost any treated wood can be used. Each pour is much less in the vertical direction and more controllable. Plan to make each pour only a few inches vertically each time, up to a foot or so ... but make the pour as much of the wall perimeter as you can manage at one time. Going up just a few inches at the time causes much less force to be applied to the forms ... much better chance the form will survive and not blow-out. Having to move the form upward is going to eliminate the wet-on-wet bonding (which isn't important in my book anyway) .... but who are we kidding, you are gonna have too much going on to make that happen anyway!

Whether block or concrete wall, be sure to have a mechanical motor driven mixer. I like the tiltable rotating drum type. I'm on my second one.