What kind of mortar for repointing?
Hi all!
I've spent probably ten hours on repointing subs for the past couple of years, and I'm royally confused. (Below, I'm numbering the premises that I've been told, for ease of feedback on whether they are accurate.)
Here's the problem: my house foundation (100+ years old) has fieldstones with large voids in the mortar (big enough to put my arm in).
My foundation also has occasional spalling brick with gaps in the mortar.
- From what I've been told, the foundation is going to take on some water no matter what. (Is this true? It might be.)
- Thus, I should want the infiltrated water to slowly wash away the mortar (which is easily repointable). This is much better than having infiltrated water cause fieldstones to crack or bricks to spall (both of which are much harder to replace).
If the mortar is harder than the fieldstone/brick, so the story goes, then the water will go through the fieldstone/brick, freeze, and crack it. (I'm in a very cold climate.) Old brick, so the internet says unhelpfully, is somewhere between 220 and 4500 PSI.
Thus, many Reddit threads, and limestone salesmen, have insisted that I MUST use natural hydraulic lime (NHL) to repoint both foundations. They insist that any amount of portland cement is a disaster, and that I must use the same material as was originally used (presumably lime).
- They also say that NHL is self-healing, because it cures with water rather than with air. That sounds good, if true.
But whenever I talk to anybody at a masonry supply store, they look at me like I have two heads. They've never heard of anybody patching with NHL. (And I can only find one place in the entire northeast that sells NHL.) They tell me that I'm wildly overthinking the problem. Am I really better-educated on this than all the masons in my city?
And if NHL 2.0 has a compressive strength of 290-1000 PSI, why is that any softer (and thus better) than Type N (750 PSI) or Type O (300 PSI)?
Is it any different for fieldstone than for brick?
Any help would be greatly appreciated! (I want to do it right, but if I had just spent those ten hours of research on using portland cement like everyone else, I'd probably be halfway finished the job already...)