How long till new sand-cement render can be skimmed?

I need to do quite a lot of patch repairs (mostly where I've chased out elctrical cable runs) on an internal wall which had been previously sand- cement rendered up to 1m, presumably due to s damp problem at some time in the past. No sign of damp now, but I'd rather do the repairs properly with similar sand-cement basecoat to avoid potentially compromising things. One area is about 2'x3' though. I've got a plasterer booked to skim the whole room afterwards.

Question - how long should my repairs be left to cure before overskimming? I've been googling and advice seems conflicted as to whether it should be left for weeks until it's bone dry, or done within a day so it's deliberately still damp!

I'm on a rather rigid schedule, in that I have the plasterer booked to start here on a Wednesday (I doubt he'll be skimming till Thursday though), and I was hoping to do my stuff the previous Sunday (I get back from holiday on the Saturday). Will that work? Or do I need to do it tonight after work, which I *really* don't want to do but is the only other realistic option, giving a gap of 2.5 weeks?

Thanks

Reply to
Lobster
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In my recent experience patching up an old garden wall, an inch depth of render will be dry enough to take the next layer in 48 hours. Do it tonight, albeit in a slap happy fashion. Doesn't have to perfect, but it needs to be dry by Wednesday :-)

Reply to
stuart noble

Either will work, but they work in different ways. Finish coat can be applied direct in 24-48 hours and will bond into the cement. After that, the cement will have set too much for a direct cement bond, and it will need to be done as for a reskim - PVA'ed first, which ideally wants the cement set a bit more, and the wall drier.

If you have a plasterer for more than a day, why not get the plasterer to do it?

Reply to
Andrew Gabriel

On 06 Oct 2014, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) grunted:

Ah OK - makes sense. Does that mean though that I'm Ok doing it just

*outside* that 24-48 hr window (ie, in my case it would probably be 4 days.

Well yes, the obvious answer! Just that I've already got this guy booked with a fixed quote (which I already think is pretty high) and don't want to start renegotiating. Plus I can easily do this bit myself (ie for the cost of materials); I'm just not sure about the timing.

Thanks

Reply to
Lobster

Just reread the OP, and given that it's just patches, the wall is going to have to be PVA'ed anyway, so you might as well do it ASAP. It will probably dry faster than if you were rendering a large area too.

Note that if the sand/cement render is to protect against damp, it will have had a waterproofer addmix added to the mix. You can buy combined plasticiser/waterproofer addmix (note that you only use it sparingly). If you don't use that, you might find it tracks enough damp though to show the patches afterwards.

Reply to
Andrew Gabriel

perfectly OK to skim damp, but dont DECORATE till its properly dried.

skimming works by setting, paint works by truing, more or less.

Reply to
The Natural Philosopher

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