On Monday, 28 January 2019 18:37:47 UTC, wrote:
On Monday, January 28, 2019 at 12:40:45 PM UTC-5, tabby wrote:

During normal operation, damp seeps in from the ground & evaporates from the surface. If the surface is sealed that evaporation stops, and the stone gets wetter. Try it for yourself, place 2 stones or tiles onto the earth & cover one with plastic sheet, weighing it down all round. Damp is one of those topics on which misinformation abounds.


NT

You do not understand how an exterior stone walk is bedded, do you? Done properly, there will be 4"- 6" of stone, 4" of sans, then the topping. Which, unless it is concrete, is seldom grouted solid. Not 'never', but seldom.

Private stone walkways are not usually constructed that way.

The entire 'system' moves and shifts with temperature, substrate expansion and contraction due to moisture and so forth. But, even when cut into dense clay, there is little or no need for evaporation through the top. In high moisture conditions, the entire system below the surface will remain damp and saturated. Transpiration is both too slow and to imprecise to be of concern.

What is necessary is to prevent differential freezing from the top down - that is what destroys grouted pavers.

not just differential freezing, any freeze/thaw cycling when too much water is present causes spalling.

And that is why *EITHER* great care is taken to match the grout density to the paver density, *OR* the surface must be rendered impervious to moisture. If one is lucky enough to have a mason trained in the fine art of grouting, then that is the ideal.

Now, if this were to be an indoor application, then you would be absolutely correct - either a vapor barrier must be installed below the top layer (which also becomes a "paper" joint) or the top layer must be left unsealed. Note that indoor applications are seldom exposed to freeze-thaw cycles. That is why all if this suddenly becomes much more than a casual exercise.

indeed, though indoor construction is not the same as outdoor, except for a small number of historic properties


NT