Here is a question for all you stone foundation veterans: My stone foundation is in mixed but OK shape - there is one large 1/4-1/2" crack, and a number of gaps large enough to fit a few fingers, but with a decent sized cavity behind them. The foundation has a lot of old lime mortar, plus a modest amount of portland cement patching on certain walls. I understand the prevailing wisdom about how portland cement should not be used to seal up an old foundation that already has lime mortar because it will trap the moisture and degrade the remaining lime mortar.
Now... I am looking to do a couple things:
1. Get the big cracks and cavities locked up tight to keep the wall sound. (Planning some drainage improvements on the outside, but want to feel good about the state of the foundation before I start digging out there...)
I am wondering if squeezing grout into the larger cavities (particularly the crack) might be most effective in those locations because a runnier grout plus gravity will go places that no mason's tool can. I'm thinking that if used strategically, my foundation will still breathe fine
2. Do some basic re-pointing in the areas that have crumbling mortar (some of which is portland based). Any downside to using lime mortar in areas where the portland is starting to break away?
3. Re-morter the junction between foundation and sill (and POSSIBLY laying a new bed of mortar for the sill in a couple sports that need sill work). Do I go for pure strength or something with a little more plasticity to get along better with my ever-settling foundation?
Go with Lime mortar, grout bag injection is acceptable just do not get the mix too thin. If your foundation is shifting the lime mortar will give with it and lime will self heal minor cracking, whereas portland just cracks. Removing as much of the previous portland repairs as possible is advised.
I'm looking at the same issue in the near future. The small portion of my foundation that remains visible has been worked on in the past with Portland based mortar, the removal of which seems nearly impossible. The "Over splash" is between 1/16" to 1/4" in places. I'm thinking about using a grinder to gently remove as much existing mortar as possible and then using a large beaded tuck pointing tool. I'm not looking forward to the previous pointing job effecting my finish product but what can I do? I had thought about Ram Setting metal lath over the foundation and parging it, it's that ugly! In the end I guess an ugly pointing job's preferable. Any suggestions are greatly appreciated....