Happy Bastille Day, also brother Bill’s birthday-big celebrations for him in Paris every year. I was going to call this Concrete Commonsense but it seemed redundant. Concrete, that Roman miracle of burned limestone that enabled the Pantheon to stand with the largest masonry dome in the world for 2000 years is truly gravel superglue. That being said, what more can I add?
- One never “pours” concrete, one “places” concrete. If it is so soupy that it “pours”, it is too watery to be strong. Adding water has to be precise, because the mixture is one of cement (often used incorrectly to describe, synechdotally, perhaps, the whole compound; and yes it is a compound, not a mixture, where the water has to be precisely enough to hydrate without extra to make it too slippery, or as aforementioned, soupy), water, and washed sand or gravel. If you don’t get the mix right, you will have cracks and breakage. And let it cure properly, usually in a 28 day time frame (there must be a parallel with rehab programs there, but I won’t touch it here!). Sun, rain, and uneven evaporation (particularly caused by those pesky “vapor barriers” of poly under) will curl the final product.
- Wash your sand or gravel. I have seen large lumps of sod and dirt in finished concrete walls when the forms were stripped, how embarrassing. Avoid cold joints, if you schedule your placement around noon, and the driver for the second load stops for lunch you may spend a lot of time grouting, or worse, re-“placing”. I have seen 40′ gravelly seams across the back of a basement wall- fortunately not a retaining wall. (And if you are using your basement wall as a retaining wall, design it that way! Spend the money on a structural design with all that #5 rebar, counterfort footings, and 30 times the diameter laps.)
- Formwork is where the money is. I remember Doug Gay, a local hero concrete man discussing having to “get physical” with the formwork in complicated multi faceted designs. Each corner adds a minimum of 3% to the overall cost (and that runs right up through the building, and no, that does not mean that a round building costs 12% less). Rectangular foundations are what is to be expected, everything else is optional- and those 30 degree angles can be the bane of construction progress and commonsense! Allons enfants!