When you need only a small volume of concrete for a project like a sundial, ready-mixed 30 kg bags are a good option. One bag usually costs less than $15, depending on the formula. The most common bagged product is concrete (a.k.a. stone) mix. Available at your local building supplier, it’s a just-add-water recipe with enough cement, sand, and crushed stone in one bag to make half a cubic foot of concrete. (Generally, all 30 kg bags of mix will produce that volume.)
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Sand mix contains cement and sand but no crushed stone. It is used anywhere you need concrete less than 5 cm thick or, because it spreads thinly, to fill cracks in old concrete. Made with a finer sand (and no crushed stone), parging mix is sticky enough to smooth over the vertical face of concrete blocks and poured concrete. Mortar mix is for laying blocks or bricks, or repointing masonry. A 30 kg sack should be enough for 12 concrete blocks (or 33 bricks).
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There are other, special-use concretes, the most popular being quick-setting mix for fence posts. This mix sets so quickly you need to straighten the post as soon as you add water to the mix in the hole.
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Quick-setting concrete for construction is both stronger and a little slower to set than fence-post mix, making it easier to work with. It’s an option for spring and autumn work, when you want the concrete to cure before there’s any freezing weather.
This article was originally published in the August 2025 issue of Cottage Life magazine.
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