Digging foundation beams prior to setting forms?

[Chuck K.]

Looking for some advice on how to dig foundation beams for my shop prior to setting up the forms. This would allow me to use my backhoe to dig beams then set forms and spread sand, lay steel etc.

I know very little about pouring concrete so am all ears here.. My hope is to save some money by putting up forms, digging beams then hire out concrete finishers for the actual pour. From my observations usually the forms are set then the beams are dug by hand which is out of the question for my back and stubborn gumbo soil. The slab will be 64'x60' this would be a lot of hand digging as I may have to go down to virgin soil, I have raised the lot ~20"

Has anyone dug beams first then put up forms and spread the sand? If so how did you keep the sand out of the freshly dug beams??

Thanks for any help.. Chuck.

 

[Alan L.]

For a slab on grade the problem with digging the beams before putting up the forms is that the stakes that hold the forms tend to cave into the beam ditch when you drive them in. I have seen it done however.

 

[jimmer2880]

I'm not trying to convince you 1 way or another. But, I recently put up a 32x32 with a 5" slab. I did all the prep-work for the slab including spreading the stone. Now that the slab has been poored for over a year, I have 6 cracks in it and am not very happy. But, the concrete guy won't back it up because he didn't do the prep work.

If/when I do it again, whomever pours the slab, does the prep also so that they have nobody to blame.

 

[Egon]

Dig and form your beams and then just pour the beams. They don't need much finishing. Then get the slab area prepared for the pour.

Then let the contractors go for it for the final pour.

Make sure you got the required rebar for joining the beam and slab in place.

 

[MarkV]

If you built grade up 20” make sure it is well compacted.

MarkV

 

[EddieWalker]

I'm assuming that when you say "beams" you are talking about footings? The ditch that is dug around the perimiter for a foundation to support the load bearing walls?

At 64ft by 60ft, it sounds like you are building a metal shop? or are you buying some very expensive, very long wood trusses to span that distance? or are you using beams to support the load of the roof, which will require additional footings inside the pad?

Who said that you have to set the footings on "virgin soil?"

Do you have an engineer or city code requiring the depth of your footings and if so, what are they? Most homes that I've built and worked on here in East Texas only have a footing that's one foot deep with half inch rebar in it that's tied to 3/8 rebar on 2ft centers for the rest of the pad that's 4 inches thick.

It's not possible to give you advice without more information.

Eddie

 

[BB_TX]

Are you planning beams across the middle also? I had a 40'x60' slab poured in 2000. They put perimeter beams as well as beams front to back and side to side across the middle. I also have black gumbo with bad expansion/contraction problems. The land sloped from the right front to the left rear a difference of maybe 18". Have only minimal hairline cracks in the slab.
Can't help on digging the beams. I did not see them do it, but I can't imagine they did it by hand. I went out most evenings to see the progress (I do not live on the land). As I remember, the beams trenches were not there one day, but were the next. And those trenches were dug pretty deep.

 

[rural2]

In 30+ years of construction I have never seen footings intentionally dug after the forms are set.
For monolithic pour... Dig footings, set edge forms by hanging form from vertical stakes, brace and line form by "kicking" additional stakes at apx. 45 deg. angle back to bank, use shovel to clean footing prior to setting re-bar, pour concrete, remove vertical stakes from footing before concrete sets up.
Stem walls... Same as above except add another form for the inside face of the stem wall and add U-shaped "jacks" or "scabs" in between vertical stakes to keep form from spreading while concrete is poured.
It's not hard to do. It's is not easy to get it right either... Concrete waits for no one! So make double sure the forms are where they are supposed to be and at the right elevation before it gets there. Oh yeah, if you are not vibrating the concrete tap the forms with a hammer or whatever to get rid of the air pockets "honeycomb" against the form.
Good luck

Looking for some advice on how to dig foundation beams for my shop prior to setting up the forms. This would allow me to use my backhoe to dig beams then set forms and spread sand, lay steel etc.

I know very little about pouring concrete so am all ears here.. My hope is to save some money by putting up forms, digging beams then hire out concrete finishers for the actual pour. From my observations usually the forms are set then the beams are dug by hand which is out of the question for my back and stubborn gumbo soil. The slab will be 64'x60' this would be a lot of hand digging as I may have to go down to virgin soil, I have raised the lot ~20"

Has anyone dug beams first then put up forms and spread the sand? If so how did you keep the sand out of the freshly dug beams??

Thanks for any help.. Chuck.

 

[ToadHill]

For forms you may want to look at pre-formed styrofoam forms. They are not only easy to assemble but they give the walls some insulation as well.

 

[GT2]

Like Eddie said, if your talking about the lower footing; My concrete guy backhoed out the ditch to full depth then just cleaned out the bottom with a flat shovel ( not much digging at all). He then set 2x10 or 12's to make the bottom forms. Then he built the stub wall forms right on top of the footing forms, added re-bar and did a two stage pour one right over the other.

 

[Chuck K.]

I should have stated that I am putting up a 40'W x 60'D metal building/shop with either 16 or 18 foot eves. Along one of the 60 walls will be a 24 wide lean to. The overall slab will be 64 x 60.

Here is what it will look like, or so I hope



If I dig and pour the footings/beams flush with the ground first then set forms, bring in sand rebar etc. would the slab adhere properly to the footings or would one want the slab to float on beams? A monolithic pour means footing slab all one continuous pour right? This type of prep and pour would seem to be more difficult. I do plan on cross beams as the engineer suggested/

I hope KHD did not mind of me showing his pic. it is what I had in mind;




I found a neat forum on cement, slump, paste, fly ash, ag mix, water reducer, etc. etc.
There is a lot more to concrete then I ever expected. I want to do it right if I can. I did a rough calculation and came with about 133 yards of concrete would be used in beams and slab. I do not want to waste 10 -15,000 dollars in concrete and materials if I screw up.. Maybe with this kind of money at stake I should leave it to a professional but I like to learn and have the satisfaction of doing it myself.

I have a civil eng. Neighbor who is drawing up plans required for the city permit he indicated he would like to go down to virgin soil meaning beams would be ~2 deep and 18 wide (width of my B/H bucket). Purchasing a smaller 12-14 bucket may be justified to save money on concrete? A friend offered to have his engineer perform a soil density test, a backscatter test was done and compaction came back greater than 95%. The fellow who has to fill out all the documentation took an unexpected leave of absence and do not know when he is coming back. Should have know it was too good to be true to get this for free so I may have to pay someone in order get the project going again.

Thanks for help and patience. Chuck.

 

[EddieWalker]

Chuck,

Sounds like you have a solid plan and design. Metal buildings have different requirments then wood ones for footings on a foundation, and it's nice to see you addressing that.

From what you have said, you don't have any experience pouring concrete. This in NOT the time to learn. Concrete is miserable,difficult and unforgiving.

Make one small mistake, and you live with it forever. Amatures make hundreds of mistakes on finishing it off. YOU WILL MESS IT UP if you do it yourself. I have some experience with pouring pads and will do 1 and 2 yards pours on my own without any problems, but after that, it gets to be too much to do without help. On a pour your size, you will need a crew of half a dozen or more!!!

If it was me, I'd contact a cement contractor that you trust and is highly recomeneded. Again, imagine what you will feel like after spending all that money and you end up with an uneven surface that looks like cr@p?

When I need a large pad poured, I like to do all the prep work myself. Level the pad, set the forms, dig the footings and install the utilities. That's all pretty basic work and something that jaut takes a little time and allot of measureing. It's not really something that you need to hire out if you can read a plan and take accurate measurements.

Then I call up my concrete guy and he comes over to inspect what I've done and get an idea of what he'll need to do the actual pour. He charges me $500 for the labor to do the pour and his cost for the concrete. He'll bring a crew of workers who all know what they are doing, along with all the tools for spreading and smoothing the concrete. He'll arrange the delivery times on the cement trucks and have it so they arrive when he's ready for them and have them unloaded and spread in just a few minutes.

It's very dificult to spread concrete over a large area and get it level. It's even harder to do this AND get a perfect finish on it. It's impossible to do this your first time and it's also impossible to do this without an experienced crew. I'm a contractor here in Texas. I make money on what I do, not what I hire out, but there is no way that I can do what they do.

Seriously, don't try to pour this yourself. YOU WILL REGRET IT.

Eddie

 

[rural2]

I can only assume that the engineering is correct. I learned a long time ago not to second guess competent Engineers, Architects and Designers. However your footings and grade beams @ 2' thick are pretty thick for the structure size. So I can only assume your soil conditions warrant this.
Yes, "monolithic" with reference to concrete placement means no cold joints thus dictating a single pour. I would suggest consulting whoever is doing your structural engineering as to whether or not you even have an option for the placement. Actually a monolithic pour, in your case, may be quicker, easier and cheaper since less form work is involved and the concrete crew will only mobilize one time.
In my experience 98% compaction is minimum. 95% may sound or seem adequate, however I can tell you I personally have not knowingly authorized concrete placement on less than a 98% + compacted sub grade. I have had to go down to native soils may times to make it happen. A possible option may be to simply excavate to native, then backfill with a "lean" cement mix. Again consult your structural engineer and crunch the $$$ numbers to determine if this would make financial sense???
From reading your second post I get the impression you already know what you need to do as far as tackling this project yourself.

 

[firemanpat2910]

I agree with eddie. this is not the project to learn concrete on. I did a walk way at my parents house that was 3' x 20 never again. I wont roof a house or pour concrete. some things are best left to the young bucks that know what they are doing.

 

[BB_TX]

I also agree with Eddie. I watched them pour my 30'x40'. There were 5 or 6 guys and they worked their butts off while the trucks were pouring and some time afterward getting it smooth and level. Then they spent probably another hour or more floating it and finishing it. They were young, but they were beat by the time they finished. And they do that every day!
Also my metal building plan called for a drip ledge around the perimeter of the foundation. Don't know if you plan on that or not.