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Should I spray foam a cobblestone foundation?

The interior of my cobblestone foundation needs to be repointed. No stones are loose, but there are deep pockets in a lot of areas.

As part of a complete gut and remodel taking place this spring, several professionals have suggested that instead of repointing with mortar, that I could simply have the insulators spray the stone with foam as they are insulating the walls and ceiling.

The exterior of the foundation looks fine. The area in question is a crawl space with a dirt floor and a large cistern that is no longer in use. The house is located in Rochester, NY, and was built around 1900.

Is this a good idea? Does the foam have enough strength and durability that I wouldn't need to repoint with mortar first? My research has turned up both sides of the argument. Are there any concerns with ants or rodents? Any guidance is very appreciated.

Asked by Jesse Watras
Posted Sun, 03/09/2014 - 18:07
Edited Mon, 03/10/2014 - 05:05


1 Answer

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If no stones are loose, and there is no evidence of recent water entry (for example, a conical pile of "fines" or silt underneath a large gap between stones), then I think it would be fine to install a layer of closed-cell spray polyurethane foam on the interior of your crawl space walls. Closed-cell spray foam can, indeed, help consolidate an old stone wall.

If you had loose stones, my advice would be different. In that case, I would repair those areas with mortar and small stones.

For more information, see Building an Unvented Crawl Space.

You might also be interested in reading these two articles:

How to Insulate a Basement Wall

Fixing a Wet Basement

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/10/2014 - 05:40

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