The next big push in our renovation is finishing the basement and opening it up to the garden. Before we get started though, I’ve been wondering if we should repoint the rubble stone foundation first. In fact, I’m actually losing a little bit of sleep over whether our poor neglected base will crumble right out from under us and back into the pile of rubble it came from. Check out the photo below and you’ll understand my anxiety – large communities of house mice would fit nicely between the chinks.
How did it get like this you ask? Well, the previous owners made a party room downstairs in the 1960′s which was lovely for them but meant the walls were covered by paneling when we bought the house – paneling that trapped moisture and caused the 150 year old mortar to crumble. Our plans involve removing the back foundation wall, replacing it with windows and excavating a foot in the back half of the basement floor for more head room in the new space (the current 6.5′ works for me, but isn’t for everyone, especially when ducking under the even lower main beam). With all the demolition planned, I’m thinking strong walls are a must.
I’ve been checking around to find someone to fix it and am beginning to realize it’s going to be EXPENSIVE to have it done correctly and thinking hey, how hard could it be to do this? Soo…
A little research yielded this nice link to Old House Web and explains why it’s important to treat historic buildings with care when re-pointing. It turns out the mortar they used before the early 20th century was different from the portland cement we use today. While not of any great significance, being from 1864, our place qualifies as historic and is definitely a candidate for old-style mortar.
So what is the right kind of mortar and why is it important? What I learned is the stuff right out of the bag from Lowe’s is not it. It’s way too hard and not porous enough for historic work. It lacks the flexibility of old mortar and can actually damage the foundation. Definitely want to stay away from that! I found another article on the same site that gets specific about what to use for old stone and how to apply it. Stone mason Ian Cramb, author of, The Art of the Stone Mason, explains:A two-step process to re-pointing stone walls “Ian’s approach involves two separate steps – tamp pointing and then finish pointing. In the first, he cuts back into the joint at least 3 inches. Then he packs the first 1 1/2 to 2 inches with mortar and a tamper. The mortar is made of 7 parts sharp sand, 1 part lime and 1 part cement (no more! he says). This initial layer is topped with finish pointing. It should be a uniform depth so it dries evenly but never less than 1/2 inch thick. Ian mixes his final pointing mortar on a board, by hand with a shovel, not in a mixer. It consists of 6 parts sharp sand, 1 part lime and 3/4 part cement. Instead of mixing up a day’s worth of mortar and adding more water as it dries out, Ian recommends mixing only as much as you’ll use in a half-hour.”
Sounds easy, right? Wait, what is ‘sharp sand’ and how is it different from smooth sand? How would I know how much I’d use up in half an hour? Do they have all this at King’s? How much will I need to buy? Hmmm…I think maybe I’ll get a couple of contractors in to see what it’s going to cost to fix things after all. At least now I’m an educated customer.