Replies

1. GBA Editor
   Martin Holladay | Apr 29, 2015 05:53am | #1

   C Darwin,
   Your first obligation is to satisfy your local building department and meet code requirements in your area.

   If you live in a rural area without inspectors, you can probably do whatever you want.

   It's true that you can make a solid, long-lasting wall out of mortared stones. How long-lasting such a wall will be depends on your skill. My own basement walls are over 8 feet high and are built with mortared stones. I built them in 1980, and they haven't moved 1/4 inch since the day they were built. But there are lots of stone basement walls in Vermont that have failed catastrophically.

   If you build stem walls for your garage, you don't necessarily need forms. But there are lots of ways you can mess things up without forms. Your excavation might collapse or cave in; you might end up with a large, unexpected void that requires a lot of concrete to fill. So I advise you to use forms.

   For a garage slab on stem walls, the quality of the material inside the walls (under the slab) is as important, or more important, than the quality of the stem walls. Ideally, the material inside your walls consists of gravel that is a good mixture of crushed stone and fines, and that has been carefully compacted in a series of shallow lifts. Your top layer should be at least 4 inches of crushed stone without fines.

2. Expert Member
   MALCOLM TAYLOR | Apr 29, 2015 11:42am | #2

   You may be able to dig a 42" deep trench that will not collapse, but it will be considerably wider that the 8" you need for your walls, so it will end up using a lot more concrete. It will also have an uneven exterior surface which may make it susceptible to front heave by giving the frozen soil a purchase point.
   Mixing your own concrete stops making sense at a remarkably small amount. I'd say in most situations less than a cubic yard. You end up with an inconsistent strength, load joints between pours, and a job that takes days rather than hours. It can be very fulfilling work, but usually doesn't save any money. I don't mean to discourage you, just want you to know that you are getting into.

3. 
   charliedarwin | Apr 29, 2015 01:29pm | #3

   I did not know frost could push up a jagged cement pour.
   That requires a very smooth rock wall--pretty hard.

   So I guess pour concrete myself.
   To get walls straight, can I just put in Styrofoam on both sides and leave in ground?
   Or will it break down and possibly let walls buckle in/out?
   I could poke in rebar anywhere I want then into the cheap white Styrofoam?
   I would just like to leave foam in ground and then pile dirt against foam before pouring.
   Pouring I would take a whole day?

4. 
   rocket190 | Apr 29, 2015 10:08pm | #4

   Mixing your own concrete would be idiotic. It takes sixty 60# bags of dry concrete mix to make one cubic yard of concrete. At $2-3 per bag your material only costs are much higher per cubic yard than what it would cost to have ready mix delivered.

   I like DIY, so I know where you are coming from, but it'd make more sense to build the forms. Fwiw, you can buy icf forms, but again, after buying forms and concrete, it's almost always cheaper to have a professional do it.

5. 
   rocket190 | Apr 29, 2015 10:10pm | #5

   Another simpler option would be to pour a concrete footing and then lay up a block wall.

6. Expert Member
   MALCOLM TAYLOR | Apr 29, 2015 10:45pm | #6

   C. Darwin,
   You can cobble together forms out of any manner of things you'd want to try. Poke rebar through them wherever you desire. Unfortunately, the chances of you ending up with anything resembling what a builder would do is fairly remote.