I’ve always heard that you should use a soft lime mortar (type o?) when repointing or repairing old brickwork. I’ve also had this recommended when working on old stone foundations and walls and have followed the recommendation.
Recently a contractor friend stopped by to see some work I’m doing on an 1821 farmhouse where I will eventually have to do some re-mortaring of the stone foundation. He commented and recommended that I use hydraulic cement for the repairs, not because of water issues but because it’s “sticky” and expands as it cures.
Now the questions: I understand why you’d use soft mortar with old bricks, but why with stone? Is it because of incompatibility with the old mortar? Is my friend off-base with his recommendation of hydraulic cement?
Thanks in advance.
DW
Replies
Yes, your friend is off-base. Using a cement (like U-Lok) is fine to plug a hole but it should not be used in joints. First of all the working time is about 3-5 minutes, temperature-dependent, making it very tough to tool. It is rock hard after 30 minutes. Second, it is VERY expensive compared to normal mortar. I don't see why you can't use regular mortar if you stone isn't on the soft side - you should consider using coarse buff sand and buff dye so you don't get a result that is too 'grey' which would look odd on an 1821 foundation.
T. Jeffery Clarke
Thought I knew something about the technique. I found out, by doing some research , that I knew less than I originally thought. IMHO one of the better and authoritative sources.
http://www2.cr.nps.gov/tps/briefs/brief02.htm#Mortar Type and Mix
Lots of information there if you look around these sites. Cool.
I've worked a bit with hydaulic cement before and didn't think it was the right tool for the job. Thanks for confirming my suspicions. This foundation is a mess. I don't know how many people have attempted to patch things together over the years. There are smears of various colored mortars all over some parts, others are in great (untouched and solid) shape. Someone even attempted to deal with rot where ####corner post meets the sill by filling the void with cement! I actually think that I am lucky that the rot continued so that I could just pop out the cement (and then cut back the post and sill to solid wood and joint in new pieces).
Everyday is another adventure...
DW