What do you do when you’re ready to start snapping chalk lines for the walls on a new slab, but the slab is wet and more rain is on the way? You could answer, “Head for the nearest coffee shop.” But that’s not it.
I go to the local rental yard and get a “weed burner.” It’s simply a 5-gal. propane tank with a 6-ft. hose and a torch nozzle. Next, I use the burner to dry a 6-in. wide path on the slab in the general area of a wall. Then I snap the wall lines and spray them with quick-drying lacquer (it comes in an aerosol can). After a couple of minutes the line is there to stay, regardless of rain or constant sweeping.
—Gil Meador, Jacksonville, OR
Edited by Charles Miller
From Fine Homebuilding #47
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Do you think we're not supposed to notice that the same tips keep cropping up ?
Excellent. I've struggled to keep chalk lines on all sorts of things outdoors for years especially this time of year. Many years ago, while I and my crew were doing a large room addition on an old home, we found an big cardboard oatmeal container in the owner's garage. Inside a red powder which we recognized immediately. Red lead. We loaded up our chalk boxes and used that stuff for months in framing, masonry and concrete projects. Turned out it was poisonous and I haven't seen any since, but, man, those chalk lines were permanent.
That might really screw up any silane barrier for controlling curing.
Why not just snap some disposable twine and leave it in the concrete? No renting fancy gear. No damage to the concrete from disturbing the curing process. But really, are you saving any time? You can't erect the walls until the concrete has attained sufficient strength. ..So, you snap some lines and then go to the coffee shop?? The spray lacquer is a good idea though.
I've been doing this for many years
@Suburbanguy I would hardly think of a weed burner as fancy gear. It's just a simple tool like a cigarette lighter. I purchased one mainly so I can melt snow from the tops of walls, roofs, floor joists etc.You said " You can't erect the walls until the concrete has attained sufficient strength" What does that have to do with the rain or wet concrete? the point is when you are ready you need a torch. The concrete does not have to be completely cured to build on. It is hard enough by the next day. Yes, there would bee a few scratches here and there, but that would be about as relevant as wained lumber or subfloor plywood sheathing with all it's surface flaws.
Aquanet hairspray or similar is a cheaper alternative than laquer and works the same. Try striping a parking lot with red chalk and Aquanet. Those lines can only be mechanically removed.
Only drawback I see is that this is bad idea if the home will later have stained concrete floors.