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Question DetailsAsked on 2/27/2016

How do you seal a basement with sandstone mortor?

The foundation if made with rock with sandstone mortar, the sand constantly is "shedding" where there is sand on the floor
How do I seal the basement or what can I seal the foundation to prevent the sand from shedding

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1 Answer


Not sure what you mean by "sandstone mortar" - unless you mean just normal mortar, which his about 1/2 sand. Generally, if the mortar is "sanding" it is a lime mortar (as opposed to cement based) and is breaking down due to moisture - so sealing the inside just traps the water and promotes the softening and disintegration. In that sort of case, if you tape a piece of plastic sheeting over the wall (say a large plastic garbage bag or dry cleaners garmet bag cut and folded out and tightly taped on, in a day or two you will get visible condensation or even running condensation on the bag - that is indication of significant water migration through the wall.

For that case, exterior waterproofing is what is needed - for a rock foundation repointing the mortar if needed first. Then if wall is in poor but acceptable (does not need total rebuilding) condition placing a concrete wall structurally tied to it on the outside, if in good condition other than the mortar flaking just the repointing. Then a bitumastic sealer sprayed or troweled on the entire outside surface to above ground level, overlain by waterproof membrane in many cases, and french drain as applicable, then backfill. Plus repointing on the inside with a water resistant (not waterproof) latex modified mortar.

I would say find a reputable Masonry contractor to look at it and advise on the condition of the wall and the repointing - if he says the outside needs excavation and waterproofing then you will likely need a Basement Waterproofing contractor for that part of the work at least.

Answered 4 years ago by LCD

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