Stone Foundation Wall Repair

[Banks]

Okay, I've looked through and only found one topic for this that helped me out a little, but I still have questions. I'm specifying a repair for an existing stone wall foundation that would involve replacing the loose and deteriorated mortar and retuck pointing with new mortar. This is for an old farm house, and I don't think aesthetics play any issue.

Here's the question - do I need to use a mortar that resembles the composition of the original mortar, or can I go with a portland cement based mortar. I know with historical brick restoration you use the lime based mortar because you want something similar to match the soft brick, but these are tough stones so I don't know if it's really required.

Thoughts?...

 

[dik]

Yes... you want to use a high lime mortar that is 'soft' and undergoes plastic deformation. Check my brief article on SlideRuleEra's site...

Dik

 

[dcarr82775]

I agree, you need to use materials similar to what is there already.

 

[Ron]

Well...I would agree with dik and dcarr except for one thing...it is a stone foundation. For old manufactured brick, I agree that the mortar should not be significantly stronger than the old mortar...that's because it can cause surface flaking problems with the brick; however, with stone, the same problems do not occur.

Make the mortar as strong and durable as practicable, assuming you have competent stone materials to which you will bond.

 

[dik]

Ron:

With the softer mortar, you get greater plasticity of the wall. Strength is not normally an issue with the large heavy stone walls. You can have reasonable strength and durability using 'modern' materials.

Some of the earlier walls have failed because there were not enough hydraulic impurities in the lime used. With newer mortars, there is a greater purity to the lime and, hence, little hydraulic capability... the reason for adding cement or masonry cement...

Dik