pt post footings

Cody · December 18, 2007, 06:43:34 PM

Hello everyone,
I am planning a new project coming up 16 x 24 shed/ guest house. I built the last house on a slab and I hate it. (The slab that is) This one I am going to use 4x6 post. They are already in the ground but need to come out since they are not square. I also realize I need some big footings due to very poor soil. (shelby loam) I would like to build footings from concrete block instead of poured concrete is this possible?? I know they make a 16 x 16 x 8 block but it doesn't exist around here (rural) so I was thinking of (2) 16 x 8 x 8 blocks side by side with two more on top in the opposite direction filled with rebar and concrete. It would look like a cube with a post anchor on top. Is there any concern with footings being too big? It might look like overkill but blocks are cheap and easy to maneuver and might cut down on the amount of mixing needed. Any thought on this . . .
Thanks a bunch - Cody

glenn kangiser · December 18, 2007, 08:14:35 PM

May not be a concern, but blocks are rather weak and doing it that way you have 4 individual cells on end that may or may not have any problems. Possibly if you could get a rebar loop in the center to tie everything together?

Just thinking -- maybe others will have better ideas.

December 18, 2007, 08:18:28 PM

If you have poor soil I don't think 16x16 is big enough but then I don't know for sure what you mean by poor. I think you'd be ahead by cutting a nice tight hole to your desired size and depth and pouring in 8 to 12" concrete with a rebar # in the middle of the depth. You won't be out much more concrete than your original plans and you won't use any blocks.

ScottA · December 18, 2007, 08:21:07 PM

Oh and FYI one 80# bag of concrete will fill 3 blocks.

glenn kangiser · December 18, 2007, 08:30:22 PM

I think Scott's idea is good -- with rebar it would probably be stronger than the block cells and use no more concrete as he said - then just extend the post the other 8 or so inches. Probably cheaper than all those blocks too. The hole can be the form

December 18, 2007, 09:21:12 PM

I'll throw in my 0.02. I have fretted with pole foundations for 6 months and I have found that concrete is a poor choice.
First, it doesn't drain so your posts won't last as long ....and

Second, it doesn't usually go deep enough to stabilize in loamy soil.

I would use gravel. I went 1 foot below the anticipated bottom of my hole and poured in driveway gravel well compacted. I used gravel dust to pack around the sides of the pole. This gives you the added benefit of being able to pour some type of preservative around the pole once in a while. An oily preservative also kills termites.

Redoverfarm · December 18, 2007, 10:36:10 PM

Cody have you considered using flue blocks. Then fill the inside void 8"X8" with concrete and rebar. I just finished laying this type of arraignment for a porch. The flue block are 16"X16"X8"(actually 15-5/8" X 7-1/2"). Of course you should pour at least a 8 or 10" footing 24"square for each. Once completed you could parge the face and add stone (or cultured stone)to each. More than enough for the size of your structure.

Cody · December 19, 2007, 08:39:40 AM

Thank You everyone for your response. The reason I am having trouble with this is because I dont have anyone who can hand dig 2 x 2 x 40" holes. and I cant (Im having a baby next week) The local dirt guy has a 12" auger, which I already tried, no wiggle room and very small 12" footings wont work. He also has an excavator. He can dig me two (or more) 24" wide trenches 15 feet apart, 24 feet long. ideally I would fill the trench with concrete and put my brackets in wet concrete where they need to go. BUT Its too cold for that amount of concrete and too expensive. so that is why Im having trouble figuring this out. To make it more pressing if I dont get this done by the time the gound starts to thaw, its muddy and unworkable for months and I need to be out of my rental by june or sign another lease. ( Same thing as last year) So trying to build spot footings in a trench might be a new one. Thank you for ANY ideas. - Cody

Redoverfarm · December 19, 2007, 09:06:35 AM

Cody do you have someone available to help on the footings? I doubt that even if you get the fooings dug that you will be able to continue. As an alternative to digging a continuing footing you could just dig the 24" width footing to the right depth and then form up the trench to narrow it down to 24" long from the steep side. Not sure what "excavator" you are using but even if it is a large machine and he ends up digging a 36"-48" long footing the forming will bring it back to what you can work with. Just be sure that the top of the footing(concrete) will work with your grade. If using block one can be higher or lower but have to be in 8" incriments.

Good Luck

glenn kangiser · December 19, 2007, 10:30:17 PM

You could also do as Redover mentioned - individual digs to depth and only put 8 to 12 inches of concrete in the bottom then come up with a foundation grade post - back fill with gravel or use sonotube and some rebar and bring only an 8" or so pier up- or as you first mentioned -use blocks on the bigger base of concrete with rebar after the excavator does the digging for you - cross a few bars in the bottom like a tic-tac-toe the bend an L on the bottom of some and run them up through the blocks to tie it all together.

I've seen what you can do but this time of year it is still a pretty tall order.