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I finally figured out why my edges were always crumbling
For years I thought a sharp trowel edge was the key to a clean finish, so I kept mine razor thin. Last month on a big patio job in Phoenix, the foreman saw me struggling and said, 'You're rounding it off before it's ready, that's why it's tearing.' He showed me how to let the concrete set up just a bit more before hitting it with the magnesium float, and to keep a slightly thicker edge on my trowel. The difference was night and day. How do you guys judge that exact timing for your first pass?
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the_lucas1mo ago
Forget waiting, just keep it wet and work fast for a smoother finish.
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the_stella1mo ago
Exactly, that wet edge is everything. Trying to blend a dry section always leaves a visible line. The trick is to have your next batch ready and move quick before the first one sets up.
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Keep it wet and work fast" sounds good in theory, but that's how you get a weak surface. If you hit it too soon with the float, you're just pulling up water and fines. You need that initial set so the paste holds together. Rushing the first pass is what causes the tearing the original poster was talking about. Letting it firm up a little gives you something to actually work with.
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