CSI - Concrete Surrounding Insulation

Have you heard of CSI? No, not Crime Scene Investigation. I'm talking about CSI for building walls? Likey, you should not have, because I just made it up. Essentially it is the title I am giving to my basement walls that my wife and kids and I created using concrete and EPS insulation. So here is what Concrete Surrounding Insullation (CSI) looks like:


You may have heard of ICF, which stands for Insulated Concrete Forms. ICF usually come in some type of block of Styrofoam or EPS that one can stack to form the house walls and then pour full of concrete. The blocks are already engineered to fit together and provide flexibility with corners, curves and other wall features. The form becomes part of the final wall and provides a great R-value for insulating a home. Though I have not tried it, I think two people could easily setup the walls. But there are a few issues that I have with it that deterred me to try something different.

1. Price - the blocks are pretty expensive
2. Finishing the inside - You need to still finish the inside with another material
   
3. Finishing the outside - You will probably want to finish the outside with another material
4. More price - Even after the blocks being expensive, you still have to pay for the above interior and exterior finishes

So in a quest to try something different, Shirley and I decided to try pouring our own concrete walls with insulation embedded inside or sandwiched inside. And that is the more commonly know term, "Sandwich Walls". Both inside and outside surfaces could be used as finished surfaces instead of having to add other materials! Our goals were to come up with a system that two people could assemble and pour without too costly of an investment in equipment. As a result, we went to Construction Material Wholesale in Birmingham to purchase plyform, a plywood with a black coating on both sides to protect from water and provide a smooth finish to the concrete. We bought:

1. 16 - 4'x8' sheets at about $33 a sheet
2. 2"x4'x8' at about $27 per sheet
3. #4 rebar in 20' lengths
4. 100 - 1/2"x2' threaded rods with two nuts and two washers per rod
5. 1/2"x10' PVC pipes
6. 1"x2"x8' treated wood boards (0.75" thick)
   
7. 2"x4"x10' treated wood boards

We did the following to prepare for the first pour:

1. We drilled holes in the plyform panels to optimize the load of the concrete pressure on the forms. The horizontal spacing was 2' in the 8' length of the board (1', 3', 5', 7'). We used 16" vertical spacing (8", 24", 40") for the holes.
   
2. We cut EPS panels and doubled them up (4") to fit between two plyform panels.
3. We cut PVC peices into 5" and 2.25" lengths.
4. We made straps from the 1"x2" boards and drilled wholes in them to match the vertical spacing of the plyform holes.
5. We assembled the formwork in place by putting threaded rod through first plyform, a 5" PVC, a strap, the 4" of EPS, another strap, a 2.25" PVC, and then the other plyform.
6. Once all 12 holes have threaded rods through, we put the 2"x4" boards laying across the rows of threaded rod on each exterior side of the plyforms.
7. Then we placed another set of straps on the outside of this.
8. Finally, we put washers and nuts on and tightened everything up to make it rigid.
9. We tied rebar on the 5.75" side within the wall cavity both vertically and horizontally.
10. We repeated this process, placing the next set off the end of the previous.
11. Once the wall is formed, we put end caps on and braced it up with some metal stakes at the bottom and some 2"X4" at the top down to the ground.
12. We framed a door opening inside the forms.
13. We put nailers and keyways in the form cavities.
    
14. We poured it full of concrete to a height of 48".
15. We let the concrete sit a day or two and removed the 2"x4" boards, the rods, and the forms.
16. We cleaned the forms up some.

We did subsequent pours:

1. We reassembled the forms with the bottom set of holes in the plyform lined up with the top set of holes from the previous pour and repeated the process to result in an additional 32" of height.
2. We repeated again (including door and window openings) for the final 32" of height to add up to 48"+32"+32"=112"

It took a good bit of time to form up for each pour. The higher we went, the more time consuming. There were a few things we learned along the way and would do differently if we were to do it again. First, we would ensure that the juice from the second and thrird heights did not run out onto the lower heights. Second, I would drill the holes in the plyform a little more accurately (I drilled through several at once and some of them shifted a little). This made it difficult occasionally to lineup the forms. Third, I would create a better gutter on the top for the next pour to lock into.

Overall, we are satisfied with the result, and saved about $7,000 fomr the price quoted by a company that pours solid concrete walls without the insulation in them. This picture peers through one window to the back walls.


I built a set of scaffolding brackets that I can fit into the threaded rod holes to support a set of planks for walking around. It gives me an idea of what the view should look like on the back deck.


That is the short of the story. It took us a period of 5 months to do it with me working full time in the prison, going to our kids' soccer games, and battling the freezing weather since November. We are now getting ready to frame the floor deck and go up higher :)