Rain on newly-poured concrete?

[Al-W]

Can anyone advise? After I pour some concrete (like a 4" thick pathway) for how long must it be proteced from rain?

Many thanka, Al-W

[Bob Minchin]

You want to avoid the surface being pock marked by rain spots. The concrete will still go off under water as it is a chemical change.

[The Natural Philosopher]

i..e about 4-6 hours at this time of year.

just lay plastic sheet or at the worst, bin bags over it weighted down with stones or something

[rick]

as long as the fines are not being washed out, once it has started to cure it can be fully immersed without issue

[Tim Watts]

I'd give it a day for moderate rain. As soon as the cement is mechanically stable, you should be OK.Heavy rain on unset concrete will wash the cement out of the surface and risks leaving it friable.

[NY]

It will probably also leave "stream beds" on the surface where the water has run in rivulets rather than running evenly over the whole surface.

[Al-W]

Thanks to all for the additional advice posts. One thing: Is it a good idea to use mortar plasticizer to reduce the amount of water needed? I want goo d strength, and am using rebar, because I may need to build a low wall alon g one side of the path and the underlying ground is kind of sandy in places .

Thanks again, Al