Connecticut is full of old stone, and most of it is doing fine. When a wall does start to fail, though, people tend to look at the part that has moved — the bulge, the crack, the stone that fell out — and assume that is the problem. It almost never is. It is the symptom, and the cause is behind it or underneath it.
There are really only three things that take a wall apart here. Water sitting behind it. A base that has moved. And mortar that has stopped doing its job. Everything you can see on the face traces back to one of those.
Start with the bulge, because it is the most common and the most misread. A retaining wall that is bowing outward in the middle is being pushed. Soil behind it is saturated, and saturated soil is dramatically heavier and more mobile than dry soil — plus, when it freezes, it expands directly into the back of the wall. Rebuilding the face without fixing the drainage behind it is repainting a wall that is on fire. What it needs is excavation behind, drainage stone, a perforated pipe with somewhere to actually go, and often filter fabric so the drainage does not silt up in five years.
Then there is leaning — the whole wall tipping rather than bulging in the middle. That is the base. Either the footing was never dug below the frost line, so the ground under it lifts and drops every winter until the wall is out of plumb, or it was built on soil that has since consolidated. This one cannot be repaired from the face at all. The wall comes down, the footing is dug properly, and the same stone goes back up.
Cracking is more informative than it looks. A fine, roughly vertical crack running through the mortar joints is usually seasonal movement and often stable. A crack that steps diagonally through the stones themselves, gets wider at one end, or has visibly opened since you last looked at it, is structural — something below is moving unevenly. The useful thing you can do as an owner is mark each end of the crack with a pencil and a date. If it grows over a season, that settles the question.
Failing mortar is the one case where the repair really is on the face. In old walls the mortar is meant to be softer than the stone, so that it takes the movement and the wear instead of the stone doing so. When it has weathered back — you can rake it out with a screwdriver, or it is powdery, or the joints are visibly recessed — the wall is losing its ability to shed water, and water in the joints is what freezes and pushes stones out. Repointing is raking out the failed joints to a proper depth and packing new mortar in.
One important caution on repointing an old wall: the new mortar has to be softer than the stone, and on genuinely old work that usually means a lime mortar rather than a hard modern Portland mix. This is the single most common way old New England walls get damaged by well-meant repair. A hard mortar will not yield, so the stone yields instead — the faces spall off, and you have converted a mortar problem into a stone problem that cannot be undone.
So, roughly, how to read your own wall. Mortar recessed or crumbling, stones sound and in plane: repointing. Individual stones loose or fallen, rest of the wall sound and straight: reset those stones and repoint locally. Bulging in the middle: drainage problem — the section comes down and goes back up with drainage behind it. Leaning as a whole, or a crack that is growing: the base has failed, and it is a rebuild.
It is worth doing before the wall reaches the point of falling. A wall that is bulging is still holding, and the stone in it is still good — rebuilding a section with the original stone is far cheaper than clearing a collapse, replacing lost material and repairing whatever it landed on. And on a retaining wall there is a safety question attached, especially where there is a walk, a drive or a garden below it.
We repair, repoint and rebuild stone and block walls across Fairfield County, and we will tell you honestly which of the four cases above you have — including when the answer is that your wall is fine and needs nothing. Call Green Valley Property Maintenance on (203) 456-6338.