How can I tell if my stucco is hollow?

Tap the wall firmly with your knuckles or the handle of a screwdriver, working across it in a grid. Sound stucco gives a solid, dull knock. Hollow stucco gives a lighter, drum-like note, and sometimes flexes slightly when pressed. Bulges, square-patterned cracks and loose edges around windows are other clues.

Is hollow stucco dangerous?

A small hollow spot is not an emergency, but it is a weak spot. Over time water gets behind it, the metal lath can rust and the section can crack away and fall. Large loose areas, especially high on a wall or over a walkway, should be looked at sooner rather than later.

Can you just paint over hollow stucco?

Paint will cover it for a while, but it cannot reattach it. The loose section keeps moving and cracking, and when it lets go it takes the paint with it. Hollow areas should be cut out and rebuilt before the wall is primed and painted.

Will power washing damage hollow stucco?

It can. Water forced into a crack around a hollow section can open it further or knock loose stucco off the wall. That is why walls are tapped and the hollow areas are marked before the wash, so those sections can be washed gently or by hand.

Hollow Stucco: Find It Before You Paint

Stucco that sounds hollow when tapped has separated from the lath or the wall behind it. It can look perfect, but it is no longer held in place, and a patch or a coat of paint over it fails with it. It is found by tapping each wall before the wash, marked, cut back to sound edges and rebuilt in layers, then textured, primed and painted.

A stucco wall can look perfectly sound from the street and still have a section that is no longer attached to the house. You only find it by touch, or by sound: a light, hollow knock where the rest of the wall gives a solid one. It is called delamination, and it is one of the things a careful painter checks for before the wash, not after.

What is hollow or delaminated stucco?

Stucco is applied in layers. On most frame houses in San Diego County it goes over building paper and metal lath fastened to the framing, or directly onto block or concrete. It holds because it is keyed into the lath or adhered to the surface underneath. Delamination is when that bond fails and a section of stucco separates from what holds it.

There are two common forms:

The whole stucco layer coming away from the lath or the masonry behind it, often over a fairly large area.
The finish coat separating from the base coat under it, usually as smaller loose patches or a skin that cracks and lifts.

Both sound hollow. Both look fine until they crack.

What causes it?

Water behind the stucco. A leak at a window, a roof edge or a failed caulk joint lets water run behind the surface. Over years it weakens the bond and rusts the lath.
Rusting lath near the coast. In salt air, as in Imperial Beach, metal lath and fasteners corrode sooner, and corroded lath stops holding.
Movement. Settlement, the daily swing between hot afternoons and cool nights inland, and the occasional earthquake all stress the bond.
Impact. A ladder, a ball, a car door or a branch hitting the same spot.
Old repairs. Patches that were never properly keyed into the surrounding wall, a common sight on older tracts like many in Chula Vista.
Original workmanship. A coat applied in poor conditions or over a surface that was not prepared.

How is it found?

By tapping, wall by wall. It takes patience, and it is worth doing before any paint plan is settled.

Tap in a grid. Use knuckles, the handle of a screwdriver or a small plastic mallet, working across each elevation from top to bottom.
Listen for the change. A solid wall gives a dull, firm knock. A hollow section rings lighter, like a drum.
Press gently. Loose stucco sometimes flexes or moves under the hand.
Look for clues. Bulges, cracks that form a square or rectangular pattern, cracks that are wider at one edge, and loose stucco around windows, doors and the base of the wall.
Mark the edges. Each hollow area is outlined with tape or chalk so it is visible during the wash and the repairs.

On a hillside house with tall walls, as in much of Spring Valley, the upper walls take a ladder or scaffold to reach. Ebenezer is certified in Scaffold Safety and Fall Protection, two of his 22 certifications, which matters when the check has to happen two stories up.

Why does it matter before painting?

Three reasons, and they compound.

The wash can make it worse. Water forced into a crack around a hollow section can open it up or blow loose stucco off the wall. Knowing where the hollow areas are lets them be washed gently or by hand.

A patch over it does not hold. Filling the crack around a hollow section and painting over it treats the symptom. The section underneath is still loose, still moving, and the crack returns, often bigger.

Paint cannot hold it on. Paint is a thin film. However good the product, it does not reattach stucco. When a loose section finally cracks away, it takes the new paint with it.

How is it repaired?

The repair rebuilds the stucco, layer by layer, the way it was originally made.

Cut back to sound edges. The loose section is removed, and the cut is made into firmly attached stucco all round.
Check what is behind it. The building paper and the lath are inspected. Rusted lath is replaced; torn paper is repaired.
Rebuild in coats. Base coats are applied and allowed to cure between layers, in the time the product calls for. Rushing this is how a repair cracks.
Match the finish texture. The top coat is textured to match the wall around it, so the repair does not read as a patch in low sun. More on that in matching stucco texture in a repair.
Let it cure, then prime. New stucco is alkaline and needs to cure before it is primed with a masonry primer, for the time that primer’s label allows.
Paint the whole elevation, so the repaired area becomes part of one surface.

Where the line is

Ebenezer repairs hollow stucco: he cuts out the loose area, rebuilds it and blends it into the wall before he paints. Where he stops is behind the stucco. When the framing or sheathing under a loose area is wet or damaged, that is a framing repair, not stucco work, and he will tell you plainly that it belongs to another trade before anything is patched over it.

The point of finding it early is that the repair stays small. A hollow patch the size of a dinner plate, found during the repair check, is a contained repair. The same patch left behind new paint for a few winters can become a section of wall.

This is part of the stucco, drywall and wood repair that comes before every exterior Ebenezer paints. If you have tapped a wall and heard that drum-like note, ask for a free estimate. He will tap every elevation, mark what he finds and explain what each area needs before any paint is planned.