Most stone step damage is one of four things: mortar joints that have opened up, a chipped or flaking (spalled) stone face, a crack right through a tread, or a tread that has settled or sunk. Open joints and small spalls can usually be repaired in place. A tread cracked all the way through usually needs to be replaced, and steps that are sinking or tilting mean the base underneath has failed, which is a rebuild of at least that part of the steps.

So the first job is working out which one you have. This guide covers all four, with extra detail on limestone steps, which spall more than most. If your problem is a tread that rocks or wobbles when you step on it, that has its own guide: how to fix loose stone steps.

Work out what kind of damage you have

Walk the steps slowly and check each tread in turn:

  • Probe the joints with a screwdriver. Mortar that scrapes out as sand has failed.
  • Tap each stone with a rubber mallet. A hollow sound often means the stone has lost contact with what is under it.
  • Put a level on each tread. Outdoor steps should pitch slightly forward, about 1/4 inch per foot, so water runs off (that is the figure in Quikrete's guide to building steps). A tread that is flat or tipped back toward the house holds water.
  • Measure the risers. For stairs serving a house, the residential code allows no more than 3/8 inch difference between the tallest and shortest riser in a flight (IRC section R311.7.5). A step that has dropped out of line is a trip hazard even if nothing looks broken.
What you seeWhat it usually meansUsual fix
Sandy, crumbling or missing mortar between stonesMortar has worn out, often from water and freeze-thawRepoint the joints
Flaking, pitted or chipped stone faceWater and salt breaking down the surface (spalling)Patch with a stone repair mortar, or set in a new piece of stone
Crack through the full thickness of a treadThe stone has broken, sometimes because the base movedReplace the tread; fix the base first if it moved
Tread tilted, sunk or out of line with the othersThe base or footing under that step has settledLift, rebuild the base, reset or rebuild
Tread rocks underfootThe bed under the stone has let goReset the tread (see the loose steps guide)
Whole flight pulling away from the houseSettlement of the steps, or a problem with the house foundationProfessional assessment before anything else

Why stone steps break down in Massachusetts

Water is behind almost all of it. Water expands by about 9 percent when it freezes (USGS Water Science School), so every time water in a joint, a crack or the pores of the stone freezes, it pushes the gap a little wider. The Massachusetts residential code rates the whole state as a "severe" weathering area and sets a 48 inch frost depth for footings (780 CMR 51.00, Table R301.2(1)). On Cape Ann and the rest of the North Shore, steps can go through that freeze and thaw many times in a winter.

The usual things that let the water in, or keep it there:

  • Open mortar joints that nobody has repointed.
  • A downspout or roof edge dumping water on or beside the steps.
  • Treads that have lost their forward pitch, so puddles sit on them.
  • Deicers. The New York Landmarks Conservancy warns that products with ammonium nitrate or ammonium sulfate "will break down even the most durable masonry materials," and advises shoveling first, using any deicer sparingly and mixing it with sand for traction (Don't Salt Your Steps).
  • A base that was thin or poorly compacted to begin with, which lets steps settle.

Fix the water source as part of the repair. Otherwise the same joints open again after the next winter.

Repointing open mortar joints (stone or brick steps)

Repointing means raking out the failed mortar and packing in new. It is the most common stone step repair, and it is the same job on brick steps.

  1. Rake out deep enough. The National Park Service says old mortar should come out to a depth of 2 to 2.5 times the width of the joint, so the new mortar has something to grip and does not pop out (Preservation Brief 2: Repointing Mortar Joints). Use a plugging chisel and go carefully at the stone edges.
  2. Choose the mortar to suit the stone. The same brief says repointing mortar should be softer or more permeable than the stone or brick and no harder than the original mortar, because a mortar harder than the stone pushes the damage into the stone itself. That matters most on older steps and on softer stone such as limestone, sandstone and old brick. The two common bagged mortars are Type S (1,800 psi minimum compressive strength) and Type N (750 psi minimum), per Quikrete's Mason Mix data sheet citing ASTM C270. If you are not sure what the old mortar is, ask a mason before you pick the strongest bag on the shelf.
  3. Match the sand. Color comes mostly from the sand. Preservation Brief 2 says matching the sand is what gets the color and texture right.
  4. Work in the right weather. The Brick Industry Association treats 40°F to 100°F as normal masonry weather and calls for protection below 40°F, because cement's curing reaction slows or stops in the cold (BIA Technical Note 1, 2018). In practice that means spring through fall here.
  5. Tool and cure. Tool the joints when the mortar is "thumbprint hard," and in very hot, dry or windy weather mist it gently so it does not dry too fast (Quikrete Mason Mix data sheet).

If the bricks themselves are flaking or crumbling, new mortar alone will not fix the steps. Those bricks need replacing, and it is worth asking why they are staying wet.

Chips, spalls and limestone steps

Spalling is when the face of the stone flakes or breaks away. It shows up most on stones that soak up water. The ASTM standards show how big that difference is: granite sold to ASTM C615 may absorb no more than 0.40 percent of its weight in water, while low-density limestone under ASTM C568 may absorb up to 12 percent (ASTM C615, ASTM C568). A wet, porous stone that freezes is the one that spalls, which is why limestone step repair comes up so often.

There are two proper ways to fix a spall:

  • A stone repair mortar. These are mineral patching mortars made to match a type of stone. The method matters more than the product. One manufacturer's patching procedure calls for removing all the deteriorated stone plus another 1/4 inch back to sound material, cutting a square 1/2 inch shoulder around the patch, and never feathering the edges out thin (Jahn Mortars basic patching procedures, Cathedral Stone Products). The maker also runs a certification class for its mortars and says the written guide is no substitute for it, which tells you something about how much skill a good patch takes.
  • A dutchman. A mason cuts out the damaged section and sets in a new piece of matching stone. It is the usual choice for large spalls or ones in plain view.

What does not last is a thin skim of mortar or cement smeared over a flaking tread. The feathered edges are the first thing to lift, and water gets in behind the patch. On a step, a loose patch is also something to trip on.

Cracked treads and sinking steps: when it becomes a rebuild

A crack through the full thickness of a tread means you now have two stones where there used to be one, and each piece can move on its own. Replacing the tread is usually the safe answer on steps people use every day. Before you do, check whether the step under it has settled. If it has, the new stone will crack the same way.

There is one alternative worth asking about. If a dense stone such as granite has broken cleanly in two and the base under it has not moved, a mason may be able to rejoin it rather than replace it. The repair is called epoxy pinning: holes are drilled into both broken faces, the faces are coated in epoxy, and non-corrosive stainless steel rods set in epoxy tie the two pieces back together. The Sealant, Waterproofing and Restoration Institute describes this method, and notes that epoxy is the usual bonding agent for granite (SWR Institute, Exterior Stone Restoration technical bulletin). It depends on both pieces being sound, so it is not an option for a tread that is crumbling, flaking or broken into several pieces, and it is not a job for a hardware store epoxy.

A tread that has sunk or tilted tells you the support under it has moved. The fix depends on how the steps were built:

  • Mortared steps or a concrete stoop against the house are rigid, so they need a footing that frost cannot lift. The Massachusetts code sets the frost line at 48 inches (780 CMR 51.00, Table R301.2(1)). Ask your building department what it requires for steps at your house. A settled mortared stoop usually means taking the steps apart down to the footing.
  • Dry-laid steps on gravel can be lifted, given a new compacted base and reset. The base should be processed gravel (crushed stone with fines) compacted in thin layers. A granite step supplier's own guide warns that pea stone, small crushed stone and sand do not compact well and may shift or wash out (Polycor granite steps installation guide).

If several treads have moved, or the steps are sliding downhill, you are past repair. At that point it is usually a new set of steps. For entry steps at a door, the guide to choosing materials and sizes for outdoor entry steps covers the options and the code limits. For garden or landscape steps set into a slope, see the guide to building stone steps.

Can you resurface concrete steps with stone?

Yes, if the concrete is sound and not cracked, sinking or pulling away from the house. The catch is height. Stone on each tread raises every step by the thickness of the stone and its mortar bed, so the bottom step gets taller and the top step at the door gets shorter unless you plan for it. Code stairs have to stay within that 3/8 inch riser tolerance, and in Massachusetts the landing outside the door can be no more than 8 1/4 inches below the threshold, and only where the door does not swing out over the landing (780 CMR 51.00, amended R311.3). Check those numbers before ordering stone.

When to stop and call a professional

Treat the steps as a safety problem, not a looks problem, if any of these apply:

  • The steps are the main way in and out of the house and any tread moves, tilts or has dropped out of line.
  • A tread is cracked all the way through.
  • More than one step has settled, or the flight is pulling away from the house. Cracks in the house foundation near the steps need looking at before the steps do.
  • The stone is heavy. A single granite or limestone tread can weigh hundreds of pounds and is easy to drop or crack.
  • The steps are old limestone, brownstone or other soft stone, where the wrong mortar or patch does more harm than good.
  • The flight has four or more risers and no solid handrail. The residential code requires a handrail on at least one side of any flight with four or more risers (IRC R311.7.8).
  • The fix means digging. Massachusetts requires a call to Dig Safe (811) at least 72 business hours before you dig, and that includes homeowners (Eversource: Call 811).

Until it is fixed, block off a moving tread or use another door. A step that shifts underfoot is exactly the kind that causes a fall.

George Hardscaping builds stone steps and brick stairs for homes in Gloucester and across the North Shore, including Rockport, Essex, Manchester-by-the-Sea, Hamilton, Wenham, Ipswich and Beverly. If your steps have reached the point of being rebuilt or replaced, see our stone steps and brick stairs page, request an estimate, or call (781) 222-0805.