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Stone Veneer Installation Problems: Stone Falling Off, Efflorescence, Cracked Mortar, Missing Lath and Scratch Coat, Stone Buried in the Grade, and What the Fix Costs
Exterior Finishes
When Stone Falls Off a House It Is Never the Stone: The Six Ways Adhered Veneer Goes Wrong and What Each Costs to Put Right
Manufactured stone has a reputation for coming off houses, and it has earned it, but not on its own. Every piece I have ever picked up off a lawn had a clean back with a dab of dry mortar in the middle, and behind it was a wall with no scratch coat, lath stapled to foam, or one layer of house wrap doing a two-layer job. The stone was fine. The installation was a shortcut, and the shortcut lasted somewhere between one winter and eight. Here is what goes wrong, how to tell which one you have, and what fixing it costs, including the part where the sheathing behind it is wet.
The problems and their causes
| What you see | What it usually is | How to tell |
|---|---|---|
| Stones loose or on the ground, often after a hard winter | No scratch coat, or mortar dabbed in the centre instead of buttered over the whole back, or stone set dry and dusty, or set in frozen mortar. Water got behind, froze, and pushed. | Look at the back of a fallen piece: a round dab of mortar and clean edges means dabbed; a full grey back means something else let go. Look at the wall: bare lath, or foam, where the stone was. |
| Whole sections bowing or sliding | Lath fastened into foam or sheathing only, missing the studs, or no lath at all over a smooth substrate. The lath is holding the wall up and nothing is holding the lath. | Press a loose area; it moves as a sheet. Staples in foam pull out with a finger. |
| White powder or streaks (efflorescence) | Water moving through the stone and mortar and leaving its salts on the face. Normal in small amounts the first year; after that it means water is getting in and not getting out: no weep screed, no flashing at the top or the windows, or stone buried in the grade. | Where it is tells you the source: at the bottom, no drainage; under a window, no sill flashing; along the top, no cap flashing. |
| Cracked or crumbling mortar joints | Weak mix, joints not tooled, frozen while curing, or the wall moving under it. On a stud wall a crack that follows a straight line is a sheathing joint telegraphing. | Straight cracks: substrate. Random crumbling: mortar. Cracks plus loose stone: both. |
| Stone to the ground or into the patio | The manufacturer wants the stone 4 in. above grade and 2 in. above paving, with the weep screed clear. Buried stone wicks water up and splits in the freeze. | Kneel down. If you cannot see the bottom edge of the stone and the screed, it is buried. |
| Stains inside, soft drywall, musty basement corner | One layer of barrier instead of two, or none, and the scratch coat bonded to the wrap. Water that gets behind the stone sits against the sheathing with nowhere to go. | A moisture meter on the inside wall below a window, then a probe through the sheathing. The window leaks page covers the inside symptoms. |
What a correct adhered stone wall has in it, from the sheathing out
- Sound sheathing, plywood or OSB, fastened to the framing. On ICF, the foam with the webs located; the lath goes into the webs, not the foam.
- Two layers of weather-resistive barrier. The inner one is the drainage plane and stays clean; the outer one is a bond break so the scratch coat does not glue itself to the drainage plane. One layer of house wrap with mortar stuck to it is not a drainage plane, it is wallpaper.
- Flashing at every opening and every top edge, lapped into the barrier, with a weep screed at the bottom of the stone that lets the water out and holds the stone off the grade. The wall protection hub has the details and the order.
- Galvanized lath, 2.5 lb minimum, fastened into studs or webs on the manufacturer’s spacing, overlapped, cups out. Not stapled to foam. Not stapled at all, on most sheets.
- A scratch coat, 1/2 in. of mortar worked into the lath and scratched, cured before any stone goes on. The thing most skipped and the thing that matters most.
- Mortar buttered over the whole back of every stone, pressed and wiggled into the scratch coat so it squeezes out at the edges. A dab in the middle is a stone waiting for a reason to leave.
- Joints tooled, or a dry-stack product fitted tight, and nothing done below 5 C without heat and hoarding.
A quote that lists all seven is a quote from somebody who has read the installation sheet. A quote that says “stone, supplied and installed” and nothing else is the one to ask about, and the manufactured vs natural stone page explains why the cheap stone quote is nearly always the cheap wall.
What the fix costs
A few loose stones, wall otherwise sound. Take them down, chip the old mortar off the scratch coat, butter and reset. A half day at the stone minimum job, $3,500, because the crew, the mixer and the mortar show up for ten stones the same as for a wall. If the installer is still in business and it is under two years old, that is his call-back, not your cheque.
A 200 sq ft bay with stone coming off and no scratch coat behind it. There is no repair for a missing scratch coat except starting over. Tearoff of adhered stone at $6 a square foot is $1,200. Rot found in the sheathing at the corners, say 60 sq ft at $6.50, is $390. New flashing kits at the two windows at $85 each is $170. New manufactured stone, mid grade, done properly, 200 at $32 is $6,400. Bin $550. Total $8,710 before HST, $9,842.30 with. The original stone on that bay was probably quoted at $5,200. The shortcut cost $3,500 and the wall, and that is before anyone looked at the drywall inside.
Efflorescence with the stone still tight. Find the water first. A missing cap flashing at the top of a skirt or a missing sill under a window is a flashing repair, $85 an opening for the kit plus the stones that have to come off to get it in, and the stain washes off with a mild acid wash once the source is fixed. Washing the stain without fixing the source gets you the same stain next spring with a receipt.
Stone buried in the new patio. Cut the bottom course off 2 in. above the paving with a grinder and install a drip edge or screed. Cheap if done before the stone has wicked for three winters; a tearoff of the bottom two courses if not.
Whose fault, and for how long
Stone that falls off within two years is installation, nearly every time, and the installer owns it. In a new house, Tarion covers defects in work and materials for one year, water penetration through the envelope for two, and major structural for seven; stone on the lawn in year three is a conversation with the builder’s warranty department about whether a cladding failure is water penetration, and the photographs of the back of the stone are the evidence. On a renovation, the contractor’s written warranty is what you have, which is why it matters that there is one, and why the holdback on a stone job is not released until the wall has been looked at from the ladder, not the driveway.
The manufacturer’s warranty is on the stone: colour, integrity, the piece itself. It is not on the mortar, the lath or the wall, and their inspector will tell you so with the installation sheet in his hand. He will be right. Brick weep holes and flashing is the same story for brick, with a ledge and an air space instead of a scratch coat.
Questions people ask
Why is the stone falling off my house?
Almost always because it was never properly attached: mortar dabbed on the back instead of buttered, no scratch coat under it, lath stapled into foam, or stone set in freezing weather. Water got behind the stone, froze, and pushed it off. Look at the back of a fallen piece; a small round dab of mortar is the answer.
Can stone veneer be reattached?
A few stones over a sound scratch coat, yes: clean and reset them. A wall with no scratch coat or bad lath cannot be patched; it comes off and goes back on properly, at $6 a square foot to remove and about $32 to reinstall.
What is the white stuff on my stone?
Efflorescence: salts carried out of the mortar and stone by water and left on the face when it dries. A little the first year is normal. Ongoing white streaks mean water is getting behind the stone and not draining, and the location points to the missing flashing or screed.
How far should stone veneer be above the ground?
4 in. above soil and 2 in. above a hard surface like a patio or driveway, by the manufacturers, with the weep screed visible. Stone run into the grade wicks water and splits in winter, and it voids the warranty.
Does stone veneer need a vapour barrier behind it?
It needs two layers of weather-resistive barrier, a drainage plane and a bond break, plus flashing and a weep screed. The vapour barrier is a different layer on the warm side of the wall and has nothing to do with the stone. The stone cost page lists what a proper quote includes.
Price it right, or price the redo
The exterior cladding cost calculator prices stone installed by the book, with the tearoff and sheathing lines if you are replacing a wall that was not. If you have a stone quote in hand and it is a single line, the $99 review will tell you which of the seven things above it is missing before the stone is on the lawn.
Sources and further reading
- Ontario’s Building Code, Section 9.27 Cladding: the first and second planes of protection, sheathing membrane, flashing at openings and transitions, and the clearances from grade and roofs that every siding and stucco job has to meet.
- Addressing moisture and mould in your home: Health Canada: what to do when the sheathing under the siding turns out wet.
- Tarion warranty coverage: what a new-home warranty covers for cladding, stucco cracks, masonry and water penetration in years one, two and seven.
