Thursday, November 11, 2010
The top of the footer forms have to be the same level or elevation all the way around to form a level base for the concrete blocks. That is easier said than done. Our forms are old and slightly warped so we did the best we could and will fix the rest with the mortar that goes under the first and 7th course of blocks. There are different ways to setup the footer forms so that the building is square. There is the 3, 4, 5 method, batter boards and the pytagoras formula I found on p. 52 of "Earth Sheltered Houses". Having tried the math solution before when getting the lines square for the trench excavation, we thought we'd try another method. Just put up the corners and see if we can get it right by chance. We'd resort to math if we had to. So we formed the corners of the outter footer form track, put them generally in the right place and moved them around till their diagonal measurement from one corner, across the house to the other corner, was the same. That worked for us! Then we staked them with rebar so they didn't move around as we screwed the remaining boards together.
We hammered in short lengths of rebar about an 8th of an inch from each corner and ran string so that it would be easier to get the forms straight. Using a transit is so incredibly easy and a fun job. We originally tried getting each piece of wood at the correct elevation, then screwed the next board in - thinking that the whole run would be too heavy to lift repeatedly. That didn't work so well, screwing in the next board almost always changed the height of the prior board. Having the whole footer form track, outer track first, screwed together then lifting (or digging down as the case may be) each section we were working on was much easier.
We've seen where people have attached rebar to a footer form with nails and moved the rebar up or down to get it to the desired height. Maybe it's just our very rocky sub-base, but that didn't work at all for us. Pounding the rebar into the ground for one was incredibly hard and for two made getting the form to an exact height almost impossible. It also almost always messed up our square or elevation. Using different sized rocks which are all over was much easier to temporarily get the inner and outer tracks to their correct height. We also used little wooden legs in some areas. Then we jammed rocks in under big spaces under the forms all around the track. Since we made sure the pad where the footers are was basically level first, there weren't any huge gaps under the forms. We did this by using the transit and shooting all around the pad and correcting before the footers were put up.
After the outer track was at the same height all the way around, we could use the level to get the inner track close to the correct height. We then did shoot the inner track with the transit to double check. It's better that the footer forms be level with each other for a nice flat base. So using the level, I'd hold the board of the inner track up till the bubble read level with the outer track, then would lift it up a hair more than I needed to. Jeffrey would screw on little wooden legs (or we'd use rocks). When done and I let go of the board, it would read level.
To brace the footer forms against the weight of the concrete that will be poured in, we pounded rebar a couple of feet from each corner and every place two boards join together. We are using 2 foot length rebar pieces so that they can be pounded down below the top of the forms. Pounding that rebar in was not done in one day, this was very labor intensive. Having the rebar below the forms (in most cases) will make it easier to use the top of the forms to screed off the concrete.
Some pieces of rebar would just not go down anymore and we'll just work around that. We may do some additional bracing, however pounding wooden braces into the ground as is suggested in the books just isn't happening at our site. If thin rebar doesn't want to go in, there is no way wooden stakes are going in. We'll use boards and concrete blocks at ground level. We thought about putting a bunch of dirt around the forms, but then it would all have to be removed to install the footer drains.
In the drawings, the house is symmetrical with an interior mass wall being exactly in the middle and two sheer walls on either side of the house lining up exactly, I've learned that exact and perfect are two words I need to let go of on this project. They are all close enough. The footer has plenty of room on either side of where the blocks will go to make minor corrections.
Next we'll pound rebar in vertically where the cavity of the concrete blocks will be and lay 3 courses of rebar horizontally. That will be another post.