Stacked Stone/Rubble Foundation

[TRAK.Structural]

Anyone have any experience with repair mortars for old stacked stone/rubble foundation walls? I have a situation where a contractor is wanting to keep existing foundations for a home that is having some work done on the wood floor framing. The foundations are stable and mostly in tact so I think this is reasonable but I am considering trying to add some sort of parge coating to more or less provide some extra insurance. The existing stone and mortar will still take all the load, but I'm hoping there is something out there that can help to contain/confine these walls from breaking loose, any ideas?

 

[gte447f]

I would literally do nothing unless there are areas that are loose and crumbling or otherwise need repair.

 

[masonrygeek]

Just remember that any time you put a parge coat, shotcrete or coating on the masonry wall, you change how it deals with water and how it can dry out. So there are structural solutions to this problem, but don't forget about absorption, drainage and evaporation. I like fixing the joints (repointing) and just keeping an eye on it.

 

[TRAK.Structural]

Just remember that any time you put a parge coat, shotcrete or coating on the masonry wall, you change how it deals with water and how it can dry out. So there are structural solutions to this problem, but don't forget about absorption, drainage and evaporation. I like fixing the joints (repointing) and just keeping an eye on it.

Good points. Wouldn't repointing have the same effect though, considering that matching the existing mortar is not realistically going to happen?

 

[XR250]

Just remember that any time you put a parge coat, shotcrete or coating on the masonry wall, you change how it deals with water and how it can dry out. So there are structural solutions to this problem, but don't forget about absorption, drainage and evaporation. I like fixing the joints (repointing) and just keeping an eye on it.

Seems like coating it would help keep moisture out of the wall. Is this really going to be an issue on a rubble stone foundation wall?
Maybe more of an issue on a multi-wythe masonry exterior wall?

 

[masonrygeek]

For a foundation wall, the water could be coming from many different directions, especially if there is not foundation waterproofing. If the water is coming from the soil side, then putting on a non-breathable coating then you may end up trapping water in the stone. With most rubble stone walls which are so rough you may have a hard time applying a continuous coating.

For the repointing you could slow down the evaporation and that's why it may be necessary to measure the water vapor transmission of the repointing mortar. Maybe more important for a historical structure, but a little overkill for a residential stone foundation. See NPS Preservation Brief No. 2: https://www.nps.gov/orgs/1739/upload/preservation-brief-02-repointing.pdf (see p. 4).