Step 4, Structures

If you have any major structural work to do (such as making a bunker or a generator box) then now would be an excellent time. If you have already decided on a spot for your solar panels/windmill then this would also be the moment to dig any trenches and pour foundations.

Making the structures, especially the bunker took up the largest part of the whole project.

The Bunker

We started the work on the bunker by picking a spot not too far away from the house (to keep cable lengths short), in the side of a hill on our terrain. Using a small backhoe attached to a farm tractor we started digging a hole 18x18 ft, carting off the dirt that came out of the hole with the bucket on the tractor. After about half a day of work the backhoe broke, the top hinge snapped. We borrowed a much larger machine from the place where we got the backhoe attachment to finish the work.

I was very disappointed when the backhoe attachment broke (a Wallenstein GX 900, they're not too hot on engineering over there, this was the second failure (another hinge snapped a few weeks earlier) so we returned it to the factory and I will never buy a Wallenstein product again) but in the end it was probably a blessing in disguise because now we could run both the tractor and the backhoe at the same time (and it dug quite a bit faster than the small one).

After digging the hole we set four concrete blocks in the ground to mark the four corners of the bunker. I spent quite a bit of time on making sure they were absolutely level because they were to form the 'reference' for the rest of the structure. If the floor isn't level you will have all kinds of trouble later.

Next we nailed a simple square of 2x6's, laid it on the four corner blocks and put vapour barrier in the square. The reason for this is that you slow the curing rate of the concrete, which makes it much stronger. Also we placed 5/8 rebar, a double row at the edge where the walls will be, and wire mesh across the whole surface, standing on pieces of wire roughly halfway the form (so about 3" off the ground).

Then we poured the form full of concrete making sure that each batch is properly hydrated. We placed 5/8 rebar 'angles', about 1' long on each side pointing up into the the space where the walls will be, and we embedded a key made from a tapered 2x4 roughly an 1" and a half out from the edge. Later, when the walls will be poured these keys will be removed and they will ensure that the walls can not move relative to the floor. Because this will be an underground structure these measures are neccesary to deal with the pressure of the soil and the groundwater, but even if you are building aboveground it is probably good practice (even if it is a little bit more work).

In the picture you can see the concrete mill we used, an oldie I found in a barn on our terrain that was still restorable. Along the edges you can see the rebar (except the slot on the right where the door is planned) and the 'keys'.

Read the instructions on your bags of concrete as to the specific mixture requirements, use small gravel without clay as 'aggregate'. Make sure you wear your oldest clothes and gloves, concrete is very corrosive. Immediately after doing anything with concrete make sure you wash all your tools with plenty of water.

After pouring we 'screed' the surface, that is, we used a long 2x6 and dragged it across the surface until it was nice and smooth, filling out uneven bits and trimming off excess.

We let the floor solidify for two days before we continued, this time with setting the forms for the walls.

That was actually quite a bit of work, and the system that we used (it's called snap-tie) uses an awful lot of lumber to give the forms the required strength.

At the spot where the door was planned we put a plywood form to prevent the concrete from being poured there (more about that later) and we placed small pieces of 2" PVC tubing where cables have to go in or out of the bunker. Better to put them in before pouring the concrete than to have to drill trough it with s 2" bit later !

After making sure that the forms were level and straight we called in the concrete truck to pour the concrete in to the walls.

Now this is where I made a major mistake ! While we were pouring the concrete into the wall I forgot to keep an eye on the doorframe, and halfway through the pouring we saw that the concrete had collected on one side of the door, with almost nothing on the other and the whole frame had been pushed out of shape !!

It took us over 2 hours to get the pieces of the doorframe out of the form (without taking it apart, that would have been a real disaster) but eventually we managed to get ALL the pieces out and we continued to pour, without a doorframe, so later we would have to cut it in.

This is where I made a second mistake, if you interrupt a pouring you have to really mix the old and the new concrete or you will end up with an ugly scar marking the break in the pouring. Mixing can be done by poking sticks or pieces of rebar into the concrete as it is being poured on top of the older layer.

The driver of the concrete truck deserves special mention here, his name is Larry, from Lyons in Sault Ste Marie Ontario. He helped us every way he could to rescue the form and when we finally succeeded I think he was as happy as we were. There *are* lots of nice people on this planet, you just have to find them :)

After the concrete truck had left we finished the top of the wall levelling it and embedding keys and rebar similar to what we had done while constructing the floor.

here is a picture of what the bunker looked like just before we removed the outside forms, and here is another one just after the forms were removed. Notice the seems between the differnt boards that make up the forms and the 'snap-ties' sticking out of the fresh concrete. Also you can see that despite our efforts the top is a little bit irregular and the total absence of a doorway :(

Before we could continue our work we had to cut a doorway in to the bunker. After asking around a bit we found that you can rent a concrete saw for about $30 per day. We decided to make the cut after the concrete was 3 days old, solid enough to not have the piece above the door come down on us and soft enough to make the cutting a bit easier. Well, it wasn't that hard, but oh boy that saw makes a lot of noise ! After making a few cross cuts (very precise work, the cuts have to meet up exactly through 6 inches of concrete) we smashed out the remainder using the sledge hammer, taking care not to damage the edges of the whole. We succeeded more or less in that, one piece got caught between the gap and the wall and ripped out a small piece from the edge.

After the doorway was in place we could start working on the form for the roof of the bunker. A poured slab 'lid' on a bunker is easier said than done. The form will have to hold up all the weight, it has to be pretty tight or there will be concrete drips all over the place and it has to be exactly level. The form we built was made on a bed of 2x4's, supported by countless vertical 2x4's interconnected at three levels to stop them from sliding.

From the 'roof' side we placed rebar and nailed a 2x8 frame around the edge, connected with 2x4's to the frame that was still sitting around the slab at the floor.

Then we poured concrete into the form, mixing it with the old mill like we did the floor (no concrete truck this time, it depends very much on how much you need if it is cost efficient or not to call in the truck, quality wise (or strength) there is no difference, it is a lot faster with the truck though!).

Halfway through the pouring of the roof the mill gave out and we had to finish the job by hand (in the dark !) and I think both Chris and myself must have cursed that mill to hell and back for giving out when it did (and we probably were equally glad that it didn't give out earlier).

The next morning the result looked like this, notice the little vent pipe placed in the concrete before it hardened to allow gases to escape from the battery room when it is operating.

I left the form in place for 5 days (call me a coward, but I really didn't feel like having a 2 ton concrete necklace), and then removed the inside supports and the plywood and plastic. The result is an amazingly smooth ceiling, it even shines ! After removing the outside form we gave the whole thing a layer of foundation coating a tar based goo that you can put on with a roller. Then we pressed thick black plastic into the still wet coating.

After all that work you have something like this. We added drainage around the outside at the base of the bunker, a weeping tile and a trench was dug to a lower laying point to get rid of the water streaming down from the hill during rain.

Note that the backfilling is not complete, I left that until all the cables are installed, no point in having to dig the same soil up twice ! When all is ready the bunker will be covered with about 2 ft of soil.

The Tracker Foundations

The trackers are freestanding structures with 10x10 ft of surface up to 15 feet above the ground. Clearly an area like that is going to have all kinds of forces acting on it in a high wind and it is very important that they are anchored solidly into planet earth (and if not you will either lose a lot of money or you'll be the proud new owner of a satellite).

We dug a large hole with the backhoe and placed a standard oil barrel in the hole and filled it up with concrete.

In the still wet concrete we placed a piece of wood with four threaded rods sticking out of it (the rods are welded together with some rebar at the bottom). When the concrete has 'set' the wood is removed (it just keeps the whole thing from sinking) and the post will be securly bolted down on the threaded rods.