I am a homeowner/diy’er. This fall I began building a short retaining wall about two feet high. I tried to prep it correctly – dug a trench, backfilled the footing with gravel and laid a french drain to remove water from behind the wall. I am using “flat” (what a misnomer) fieldstone, and I set the first course in concrete. I then set the next courses in mortar. I was about two-thirds of the way completed when the long-cold winter in Boston set in.
Well, the snow finally melted and revealed that much of the mortar between the fieldstones has failed. It is crumbling/falling out, and flaking in some places. Some of it seems like it never dried/set. The last mortar was laid days before our long freeze, so I wouldn’t think that would be the problem. I used premixed bags of mortar from a local lumber yard and from HD.
Any ideas what I might have done wrong? Someone mentioned not enough cement in the mixes? Any suggestions on how to do it correctly as I lay the final courses?
Thank you very much for your insights.
David Pineau
Replies
Might be way too much portland in the mix. Commonly available brick mortar is high in portland content and is very hard. Stone expands and contracts, along with the water that gets in the wall. Old stone walls were laid up with lime putty mortar, using little or no portland. Lime sucks up moisture and gives it off easily. The mortar is very flexible. Also, you probably shouldn't have let snow/ice get onto / into the wall. Old walls were always capped with something to prevent water intrusion.
Nick