A stone step rocks because the tread has lost full contact with whatever is under it. On mortared steps, the mortar bed has cracked or let go. On dry-laid steps, the gravel underneath has settled or washed out. The fix is the same idea for both: lift the stone, rebuild solid support under its whole footprint, reset it with a slight forward pitch, and stop the water that caused it.

This guide is only about loose, rocking or wobbling treads. If your steps are cracked, flaking, or sinking as a whole, start with the main guide to stone step repair, because those problems need a different fix.

First, find out what is holding the tread up

How you reset a loose step depends on how it was built. Look at the joints and the step next to the loose one:

  • Mortared steps have mortar in the joints and under each tread, usually sitting on concrete, block or stone risers.
  • Dry-laid steps have no mortar. Each stone sits on compacted gravel or on the step below. Many garden and slope steps are built this way.
  • Flagstone on a concrete stoop is a thin layer of stone bonded to a concrete step. When the bond fails, a flag lifts or rocks even though the concrete under it is fine.

Then test it. Press down on each corner of the tread and watch where it moves. Tap it with a rubber mallet: a hollow sound usually means a gap under the stone. And look at what is underneath if you can see it. If the concrete or masonry below the tread is itself cracked or has dropped, resetting the stone will not last; that is a base problem covered in the stone step repair guide.

Why stone treads come loose

Nearly every loose tread comes down to water, then time.

  • Freeze-thaw. Water expands by about 9 percent as it freezes (USGS). Water that gets under a tread through an open joint freezes, lifts the stone slightly and breaks the bond. The Massachusetts residential code rates the state's weathering as "severe" for this reason (780 CMR 51.00, Table R301.2(1)).
  • Lost pitch. A tread that no longer drains forward holds a puddle, and the puddle finds the joint at the back.
  • Roof water. A downspout or drip edge dumping onto the steps keeps them wet all winter.
  • A thin or partial bed. Stones set on a few dabs of mortar, or on a base that was never compacted, have little to hold them when things start moving.
  • Washout. On dry-laid steps, water running down the slope carries fines out from under the stones until they rock.

Resetting a mortared stone tread

This is a reasonable homeowner job for one tread on sound steps, in dry weather between about 40°F and 100°F. The Brick Industry Association treats that range as normal conditions for mortar work and calls for protecting fresh mortar below 40°F (BIA Technical Note 1, 2018).

  1. Lift the tread off. Wear eye protection and gloves. Get help if the stone is heavy; a thick granite or limestone tread can weigh hundreds of pounds. Pad the neighboring stones so a pry bar does not chip them.
  2. Chip out the old bed. Remove all loose, cracked or hollow mortar from the step below and from the underside of the tread, down to sound material.
  3. Clean it. Brush and vacuum out the dust. Quikrete's data sheet calls for surfaces that are clean and free of dirt and loose debris for the best bond.
  4. Dampen, do not flood. Mist both surfaces so dry stone does not suck the water out of the mortar, but leave no standing water.
  5. Mix the mortar stiff. Quikrete's test for the right consistency: a 1/2 inch layer stays on the trowel when you hold it nearly vertical (Quikrete Mason Mix data sheet). Soupy mortar shrinks and cracks.
  6. Lay a full bed, not dabs. The whole footprint of the tread needs to bear on mortar. Gaps are where water collects and where the next rocking starts.
  7. Set, tap and check. Lower the stone straight down, bed it with a rubber mallet, and check it with a level. It should be level side to side and pitch forward about 1/4 inch per foot so water runs off the front (Quikrete steps guide). That is also the steepest slope the residential code allows on a stair tread: 1 unit in 48, or 2 percent.
  8. Match the neighbors. Measure the riser above and below. On stairs serving a house, risers in a flight should not differ by more than 3/8 inch (IRC R311.7.5). A reset tread that ends up high or low is a trip hazard.
  9. Fill and tool the joints. Pack the joints full, then tool them when the mortar is thumbprint hard. Sponge mortar off the stone face before it sets.
  10. Protect it. Keep people off it while it sets, as the bag directs. In hot, dry or windy weather, mist it gently so it does not dry too fast (Quikrete data sheet).

Which mortar?

Type S has a minimum compressive strength of 1,800 psi and Type N 750 psi under ASTM C270 (Quikrete Mason Mix data sheet). Stronger is not always better. The National Park Service's guidance is that new mortar should be softer or more permeable than the stone and no harder than the original mortar (Preservation Brief 2). On older steps, or soft stone like limestone and sandstone, match what is there rather than reaching for the hardest mix.

Resetting a dry-laid tread

With no mortar involved, this is mostly about the base.

  1. Lift the stone and look at what it was sitting on. Soft, muddy or washed-out material has to come out.
  2. Rebuild the base with processed gravel (crushed stone with fines), compacted in thin layers. A granite step supplier's installation guide calls for compacting processed gravel in 3 to 4 inch layers and warns that pea stone, small crushed stone and sand do not compact well and may shift or wash out (Polycor granite steps installation guide).
  3. Reset and walk-test. Set the stone, check level and forward pitch, then stand on each corner. It should not move at all. Fix any rocking by adjusting the base, or with shims placed where they will not show, as the same guide recommends.
  4. Backfill the sides and back with compacted gravel so the stone is held in place and water drains away from it.

Loose flagstone, sagging brick steps and paver steps

Loose flagstone on a concrete stoop. If the concrete is sound, a lifted flag can be taken up, the old mortar ground or chipped off both surfaces, and the flag reset on a full mortar bed as above. If several flags are loose, look for why: a stoop that has cracked or settled will keep throwing them off.

Sagging brick steps. One or two loose bricks can be taken out, cleaned and reset with new mortar. A sag across a whole step, or steps that dip in the middle, means the base or footing has moved. Resetting bricks on top of a moving base does not hold, so that is a rebuild.

Paver steps. Paver steps are usually dry-laid, so a loose paver or step unit is reset like a dry-laid tread: lift it, rebuild and compact the base, reset it and check the pitch. Check that the units at the edges are still held in place, since a failed edge lets the whole step spread.

Why it keeps coming loose, and when to call a professional

If a tread you reset comes loose again after one winter, the mortar was probably not the problem. Look for the water: a downspout that needs to be moved, a tread that was set without enough pitch, open joints elsewhere on the steps, or soil washing onto and under the steps from the slope above. Fix that first.

Stop and get a professional involved when:

  • More than one tread is loose, or the loose tread is at the top landing by the door.
  • The steps are the main entrance and a tread moves at all. Block it off or use another door until it is fixed.
  • The tread is too heavy to lift safely.
  • The concrete or masonry under the tread is cracked, has dropped, or the steps are pulling away from the house.
  • The handrail is loose too. On a flight with four or more risers, the residential code requires a handrail on at least one side (IRC R311.7.8).

George Hardscaping builds stone steps and brick stairs for homes in Gloucester and across the North Shore. If your steps need more than a reset, see our stone steps and brick stairs page, request an estimate, or call (781) 222-0805.