Aug/091
Building a Deck, Day 4 – Pouring Concrete
DAY 4 – Pouring Concrete
Not nearly as fun as you would think – even if you think it might be the slightest bit fun. Bags of pre-mixed concrete are extremely dusty, so a mask is a must, unless you would prefer to have a mustache made of cement.
SO, how much cement will you need? The formula is rather simple. Take the radius of the tube in inches (which is ½ the diameter), multiply it by itself, then multiply it by Pi (3.14), then multiply it by the height in inches. So, an 8” tube that is 4 ft in length would be 2411.52 (4*4*3.14*48). Divide this number by 1728 – the amount of cubic inches in a cubic foot – to find out how many cubic feet of cement you will need per tube. That means for an 8” tube that is 48” in length, you would need 1.40 cubic feet of cement (figure on 1.5 cubic feet to be safe). In my case, I was planning on cutting the tubes to 40” and leave the last 8” as a wider earth-formed footer to my pier. The holes I dug were about 12” wide, so I instead would need a total of 1.68 cubic feet per hole – 4*4*3.14*40 = 2009.6 / 1728 = 1.16 cubic feet for each tube plus 6*6*3.14*8 = 904.32 / 1728 = .52 cubic feet for each footer. I rounded that up to 1.75 cubic feet when buying my cement, which is how I came up with 12 bags (Quikrete says their 80lb bags will produce approximately 0.6 cubic feet of cement).
<RANT>
So, Home Depot, I’m calling you out. When you see a guy grabbing one of those platform carts, strolling over to the bagged concrete section, don’t just stand there and watch. Better yet, when you ask him, “How’s it going?”, and he replies “Good, but these bags are heavy,” don’t just pass him buy on your way to the break room. I know, foolish me, I forgot to say the magic words, “I could use a little help here,” but for f*** sake, it is implied. I wasn’t dressed like a construction worker, I didn’t have 4 buddies helping me out, it was me by my lonesome on a Monday morning, loading 12 bags of concrete onto one of those flat pull carts, then huffing them out to the parking lot where I again had to load them onto my trailer. No help what-so-ever. Shame on me for not asking for help? Shame on you for not offering.
</RANT>
During my trip to Home Depot, I decided to further punish myself by renting a cement mixer from their rental department. My previous rant is almost negated as the guys behind the rental counter were awesome. They fully explained the ins and outs of the new-style mixer (plastic barrel, very lightweight) and that you had to hose the entire thing out before using to minimize the amount of release-agent they spray in the tumbler. I’ve only mixed cement one other time in my life, and it more like helping mix cement, as I was probably only 10.
Once I got everything home, I made sure to wrap the cement tubes in plastic before putting them in their holes. This theoretically will help prevent water from seeping into the cardboard tubes from the outside and then freezing in winter, causing a mini-frost-jacking effect. I suppose if you are required to use rebar in your piers, you probably have less to worry about. We have a relatively high water table with clay soil in our area with that holds water like a high-school grudge, so I want to do everything possible to keep water away from these piers. After wrapping the tubes, I set them in their holes (8” tubes made my Quikrete – seem as good as the Sonotube brand) and leveled them off, making sure to tack them to some scrap lumber I had to prevent them from shifting, fired up the mixer, and started mixing some cement!
Mixing and pouring cement is not an easy task. It seems easy enough…just add water. But getting the right consistency so that you can pour/slide it out of the mixer while not having it turn out runny is delicate balancing act. I followed the recommended water amount that Quikrete provides on their bags, but found the cement not nearly wet enough to work with (it was almost clay-like). After tampering with the amounts, I found the best method was to just add water with a garden hose, 1 second of flow at a time, until the cement was about the consistency of oatmeal. This would allow me to tip the mixer over the hole and run about ¾ of the cement out of the barrel, leaving me with only ¼ of the original mix that I would have to slide out with a shovel. I had to mix 11 ½ bags to fill my four 8” tubes (~40” in length with an 8” earth-formed footer that was ~12” in diameter). Oddly enough, completing the pours by myself took just over 2 hours, much faster than I originally thought. I happily returned the cement mixer to HD to take advantage of their 4 hour rental window, rather than being charged for the full 8 hours.
Before my concrete cures too much, I needed to insert a single J-bolt into the each form. This will allow me to later add a post mount to the peir, and allow for a little bit of play. I decided against the wet-cast post mounts for this specific reason – once you set them in place, they’re in and they don’t move. If you realize after the concrete cures that you’re alignment was off by 1/2″ or so, or that you’re mount is slightly twisted, you’re screwed. You have to work with what you’ve got at that point. With a J-bolt, I can align the bolt with my strings (which when put back in place should show the center line of my posts) and if it happens to be off by a little, no big deal! The post mount that accompanies the J-bolt allows you to slide it up to 1″ in either direction from center, not to mention that it simply slips over the bolt, so you can rotate it 360 degrees, ensuring that you’re posts are not skewed in relationship to each other (extremely important when trying to mount the beam on top).
