footing below grade

[dabill]

Thank you for your prompt response, however I believe I have not expressed myself adequately. My question has less to do with the slope of my proposed footing than how to make a trench footing level. The slope is only 6" across the appox. 27' of footing.
I am allowed in this part of the country to dig a trench 12" deep and have a 6" thick footing without forming. So, keeping the bottom of the trench level will mean one end will be 18" deep.
My question is: how to ensure the top of the footing is level across the entire distance if I do not use forming? Is it enough to have a string as a guide? Does concrete seek its own level? Does it require a certain mixture? Hope these questions are easier to understand.
Thank you in advance.

[Rich]

Ok.. that make more sense now. So essentially you will need to make sure the whole footing is below grade. To make sure the footing is level across the top you need to use a level. A builder's level is proferred where you can set it up and not have to move it for a time. A string will not cut it in my opinion. Concrete will seek it's own level to a point (unless you use a superplasticizer or some other admixture) then it's up to you to give it it's level.

[mreynolds]

I just did a trench footing this summer and I must admit it is the first time I ever did such a project. My excavator was very helpful is this case. Since he had his transit set up to dig my footer, when he finished we set rebar pins down the center of the trench every 3-4 feet so that the pin head would equal the top of the footer. Once the concrete got there, we poured it a little on the wet side. By attaching a screed board to an extension pole, we were able to screed the concrete from the side of the hole without even going in. It turned out pretty slick.

[Rich]

Excellent idea. If you don't mind I'll add that to the tips index that I am just getting started.. URL is http://tips.construction-resource.com - like I said it's brand new.