# how soon can i grout slate after rain?



## scotzilla (Mar 1, 2011)

we had some rain two nights ago. Its been dry but overcast since. THe slate is dry but i can tell the mortar bed is damp. When can i finish grouting?


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## oh'mike (Sep 18, 2009)

I fixed the title for you----Mike---


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## joecaption (Nov 30, 2011)

Slate is by far one of the most poris stones there is. I seal it before even installing it. Even thin set or grout can stain it.


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## scotzilla (Mar 1, 2011)

joecaption said:


> Slate is by far one of the most poris stones there is. I seal it before even installing it. Even thin set or grout can stain it.



i noticed that, its been taking a while to grout as you have to spend more time wiping it before you let it set up and leave a haze.


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## RWCustom (Oct 15, 2012)

You always want to seal natural stone prior to grouting using a deep penetrating sealer, or enhancer sealer if you want the colors to pop like the stone is wet without the shine. This keeps the dye in the grout from soaking into the pores of the stone and altering the color of the stone. This of course depends on the type and color of the stone, as well as the type and color of the grout, but regardless it's just a good habit to get into and will save you a lot of frustration in the long run. Slate can be a pain to get clean as it is and a proper sealing job prior to grouting makes a huge difference. As with any portland based grout you want to use the absolute minimum amount of moisture possible when you wipe it down to avoid diluting the color or making it splotchy (watered down in spots). Pre-sealing gives you the best chance of getting the best results and it makes grouting slate a lot easier, so it's a win any which way you look at it.


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## RWCustom (Oct 15, 2012)

I got majorly sidetracked in my previous post, sheesh!

Anyway, it'd be best to not grout over a wet "bed". If the parts of the mortar that you can see are wet then the stuff you can't see is drenched. Slate is like a sponge, literally, and the moisture/vapor will definitely affect the grout curing process. If you grout the slate with the setting bed being saturated with water then at the very least you can expect splotchy grout joints, and worse case scenario would be a weakened joint due to too much moisture/vapor while it's trying to cure.

On another note it's getting below freezing in various parts of the country at night, so I REALLY hope the weather remains above freezing for you. Wet slate and freeze/thaw can translate into some major delamination/flaking issues.  If you grouted before sealing you'll have to wait 72 hours before applying an exterior stone sealer. Once it is safe to seal it, get it sealed asap.


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