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A couple of weeks ago we had some brick-pavings re-cemented around our driveway. Now all of the grass on the lawn that runs alongside the bricks has gone very orange. I assume it was where the cement/sand mix was brushed onto the grass to clear up after the work.
I read that cement is high in alkaline. Would that have been the cause, and can grass recover naturally or should I purchase some kind of treatment, as opposed to scarifying it out and re-seeding?
I suggest you wait and see - the other risk with brushing a cement sand mix onto grass is the sand itself might be high in salts, particularly if it wasn't washed sand. If it is a salt problem, that will sit in the soil for a while, possibly some months depending on quantity, until there's been sufficient rain to flush it all away. Given the type of work you've had done though, its unlikely there's a large amount of salt in the soil; even so any attempt at reseeding won't work till the salt's disappeared, so wait and see for a while seems to be the best option. YOu might even find the grass recovers on its own eventually.
I agree that the caustic lime used in masonry is likely the culprit. Depending on how much was washed onto the grass, it could kill the grass, rather than just cause a temporary die-back. However over time it will react with CO2 in the air and turn into calcium carbonate, which is alkaline, but not caustic. A pH test will tell you if you need to make any adjustments. Depending on what kind of grass you have growing, you are looking for soil pH in the 5.0 - 7.0 range.
pH7 to pH7.5, so perhaps slightly biased toward alkaline? Do you think that's worth treating or leaving for the rain to wash through?