Depends on the stone and application we have the worst freeze thaw in the country we stay around 32 degrees so it mY freeze thaw several times a day vertical stone. No problem limestone caps steps tend to  disappear. Indiana limestone windowsills seem to be the worst. If it's blue stone good slate sandstone leave it alone
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On Mar 4, 2015, at 12:19 PM, Fred Hueston <fhueston@gmail.com> wrote:

Showers are another story and should be sealed.

On Wed, Mar 4, 2015 at 1:15 PM, Baird Standish <bairdstandish@gmail.com> wrote:
Fred, what do you think of sealing the insight of a shower?


________________________________________
From the desk of
Baird Standish
Managing Partner
Facility Specialists, LLC
15 West Highland Ave. Suite E
Philadelphia, PA 19118

On Mar 4, 2015, at 12:25 PM, Fred Hueston <fhueston@gmail.com> wrote:

Over the years I have been asked over and over again should exterior natural stone be sealed, and my answer has almost always been, NO. There are several reasons for not sealing exterior stone not to mention all the failures I have seen that can be traced back to sealers.

The following are my reasons for not sealing exterior stone:

1. Internal Moisture- I don't care how dry you think the stone is there is always internal moisture within the stone. This moisture can become trapped in a sealed stone and cause it to flake and spall. Now some of you are saying but I am using a stone impregnator this is vapor permeable(it can breathe). The key word in that sentence is vapor. Impregnators which are vapor permeable will allow vapor to escape, not liquid water. Due to the fact an exterior environment will go though not only temperature fluctuations but also humidity fluctuations causing vapor to condense into a liquid. This liquid will attempt to escape the stones pores and hence will cause pressure and the stone will flake or spall.

2. Freeze Thaw - In locations where the temperature drops below 32 degree Fahrenheit the liquid described above will freeze. The frozen water will expand causing the stone to again spall or flake.

3. Soluble salt migration - Most exterior stone is set on some type of substrate. This substrate can be a slab, directly on the ground, sand, brick or concrete wall etc. These substrates contain soluble salts which will penetrate into the back of the stone carrying these salts in a liquid form. This liquid will than migrate to the surface. If the stone is sealed than it will become trapped and the stone will flake or spall.

4. improper application- I have seen numerous failures where the sealer was not applied correctly. Leaving sealer on the surface, applying the sealer while the stone is still wet, applying the sealer to soiled stone, etc. are all improper applications.

I am using the word sealer above which is referring to stone impregnators or penetrating sealers.

--
Frederick M. Hueston
www.stoneforensics.com
office             321 514 6845      
See my specialty products at  www.godrfred.com
 
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--
Frederick M. Hueston
www.stoneforensics.com
office             321 514 6845      
See my specialty products at  www.godrfred.com
 
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