How to Anchor Into Block, Brick and Stone

Why this matters

"Masonry" on an anchor box covers walls that have almost nothing in common. A solid brick wall three wythes thick, a hollow concrete block with 1-1/4 in of concrete before the void, a single layer of brick veneer standing an inch off a wood-framed wall, and manufactured stone glued to metal lath all look like masonry from the yard, and an anchor that holds a ton in one barely holds itself in another. Most masonry anchor failures are not the wrong anchor for the load. They are the right anchor for a substrate that was not there. This card owns identifying the substrate. Choosing the anchor family for it is covered in The Anchor Types and What Each Needs From the Base Material, and sizing to the load in How to Choose an Anchor for What You Are Hanging.

Before you drill: dust and what is behind

Drilling masonry releases respirable crystalline silica. Use a drill with a dust shroud connected to a vacuum with a filter rated for it; that is the engineering control OSHA's construction silica standard (29 CFR 1926.1153, Table 1) names for handheld drills, and a respirator, where one is needed, goes under a written program per 29 CFR 1910.134. See related: Respirable Crystalline Silica and the Construction Standard. Painted brick on a pre-1978 house may carry lead paint; see Lead Paint: Where It Hides in an Older House. Scan for services before drilling an exterior wall too: meters, service entrances, hose bibs and dryer vents all put something in or behind the masonry, and brick veneer has a whole framed wall behind it. See related: How to Scan a Wall Before You Cut or Drill.

The substrate test, step by step

Step 1: Read the wall from the outside. Look at the bottom course of brick for weep holes, small open head joints or tubes left in the mortar just above the foundation. Weeps are the mark of veneer with a drainage space behind it; the 2021 IRC (R703.8.6, as adopted) requires them at no more than 33 in on center. Look at the bond: in a solid multi-wythe brick wall, every fifth to seventh course often has bricks turned end-out (headers) tying the layers together, and a wall of all stretchers (long faces) is usually a single wythe. Concrete block shows its gray 8 by 16 in units, often under paint or stucco.

Step 2: Read the thickness at an opening. At a window or door, measure from the exterior face to the interior face of the wall. A brick veneer wall over a 2x4 frame runs roughly 9 to 10 in: about 3-5/8 in of brick, about 1 in of air space, the sheathing, the stud and the drywall. A solid brick wall of two or three wythes is usually 8 in or more of masonry with plaster or drywall directly on it. A block wall is 8 in or so of block, often with furring and drywall inside.

Step 3: Drill a test hole, rotation only. In a spot that will be hidden under the fixture or bracket, drill a small hole with a masonry bit with the hammer off, and watch two things: the dust and the bit.

• The dust. Red or orange dust is clay brick; gray is concrete block, concrete or most mortar; gray and white, or mixed colors, is stone or a stone veneer and its mortar.
• The bit. A sudden drop in resistance means the bit has broken into a void. Note the depth when it happens.

Step 4: Interpret the depth. That depth tells you what you are in.

  What the test bit meets, drilled from the outside

  hollow block   |shell ~1-1/4|  cell, void  |shell|
                  drop at about 1-1/4 in, gray dust

  grouted block  |shell|===== grout ======|shell|
                  no drop, gray dust all the way

  solid brick    |brick|m|brick|m|brick|
                  no drop, red dust, 8 in or more

  brick veneer   |brick 3-5/8|air ~1|sheathing|stud
                  drop at about 3-5/8, then wood

  adhered stone  |stone+mortar|lath|paper|sheathing
                  mixed dust, then wire, then paper

Step 5: Drill a second test where the first could mislead. A block wall has grouted cells, usually where it carries reinforcing steel, at corners and around openings, and a solid bond beam at the top. One test hole in a grouted cell will tell you the whole wall is solid. Drill a second a few inches over, and on block, at each planned anchor position if the load matters.

Step 6: Decide unit or joint. In modern brick and block with Portland cement mortar, anchor into the unit, keeping at least the anchor manufacturer's minimum edge distance from the mortar joints and the unit's edges, because the anchor's published values are for the unit. In old soft brick laid in lime mortar, a light load can go into the mortar joint instead, because a joint can be repointed and a cracked historic brick cannot be replaced to match; anything heavy goes to the structure. Never put an expansion anchor in a joint on a heavy or vibrating load: mortar is the weakest material in the wall.

Step 7: Match the anchor family to what you found. Hollow block takes anchors with published values for hollow block: certain sleeve anchors and masonry screws set in the face shell, toggles through the shell into the cell, or adhesive with a screen tube that keeps the adhesive from running into the void. Wedge anchors are for solid concrete, not hollow block or brick. Grouted block and solid brick take most solid-base anchors within their published values. Veneer and adhered stone are not substrates for a structural load at all; the load goes through them to the structure behind, or somewhere else. The full family-by-substrate match is in the anchor-types card.

One test, two walls: a ductless outdoor unit

An HVAC shop is installing a ductless heat pump at a 1962 ranch house, with the outdoor unit on a wall bracket to keep it above snow. The bracket's instructions call for four anchors into solid masonry or the building structure, with a minimum value per anchor for that unit's weight. Two walls are candidates: the side wall of the house, which looks like brick, and the back wall of the attached garage, which looks like painted block.

Side wall, Steps 1 to 4. At the bottom course, open head joints every 32 in or so: weeps. The bond is all stretchers. At the side window, the wall measures about 9-1/2 in, face to face. The test hole, rotation only, throws red dust, drops into a void at about 3-5/8 in, and the bit then meets resistance again about an inch further on and starts throwing pale wood fiber: the sheathing.

That is brick veneer: one wythe of brick standing about an inch off a sheathed wood-framed wall, tied to it with small metal ties sized to hold the brick itself against wind. The veneer was not designed to carry a bracket and an outdoor unit hanging off its face, and the bracket's instructions do not accept it. Through-bolting to the framing behind the veneer would put a cantilevered, vibrating load on bolts spanning the air space and break the drainage plane in four places; the shop rules it out and the side wall is out. The decision is the substrate, made before any anchor was chosen.

Garage wall, Steps 1 to 5. Gray block units 8 by 16 in under the paint; no weeps. The test hole throws gray dust and drops at about 1-1/4 in: hollow block, the bit through the face shell and into a cell. The four planned anchor positions form a rectangle, and the shop drills a test at each:

Three positions are hollow and one is grouted. Mixing anchor types on one bracket would split the load unevenly, so the shop sets all four the same way.

Step 6, unit or joint. The garage was laid with modern mortar, so all four anchors go in the block units, at least the manufacturer's edge distance from the joints. That rules out the two positions where the bracket's slots landed on a horizontal joint; the bracket moves up 2 in so all four slots land on block faces. Cells and grout run vertically, so moving up keeps each anchor in the cell its test hole found.

Step 7, the anchor. Adhesive anchors with screen tubes, which the adhesive manufacturer publishes values for in both hollow and grouted block, with the hollow-block value as the governing one. The shop checks that the hollow-block value per anchor, at the published edge distance, meets the bracket's stated minimum per anchor, and it does with margin. The tests at the four positions are photographed. The anchor holes are drilled with the hammer off, because hammering through a face shell spalls its inside face and leaves the screen tube less shell to bear on, with a shrouded drill on a vacuum; the paint on a 1962 wall is presumed to contain lead, so that capture also catches the paint dust, and the area is wet-wiped after. The adhesive is allowed its full cure time before the unit goes on.

What the test settled. On the side wall, it ended the question in one hole: no anchor was going to be right. On the garage wall, it changed the anchor (screen-tube adhesive, not a solid-base anchor that would have been right for the one grouted cell), moved the bracket off the joints, and set the governing value at the weakest of the four positions.

What would have changed the answer. A solid two-wythe brick wall, identified by header courses and an 8 in or deeper test with no drop, would have taken solid-base anchors in the brick units within their published values. An adhered stone veneer over the block would have needed the anchors through the stone into the block behind it, with a sleeve or standoff so the bracket bears on the block rather than on the stone.

How to verify you read the wall right

Before you set the first anchor: you can name the substrate from the evidence (dust, depth, weeps, bond and thickness), not from how the wall looks; every anchor position has been test-drilled where the substrate could vary; the anchor's published values are for the substrate you found, at the edge distance you can actually achieve; and on veneer or adhered stone, the load is going to the structure behind or somewhere else. After installation, a firm pull and push on the bracket shows no movement and no cracking in the units around the anchors.

References

• International Residential Code 2021, R703.8.6 (weep holes in masonry veneer), as adopted
• OSHA respirable crystalline silica in construction, 29 CFR 1926.1153, Table 1 entry for handheld drills
• Anchor and adhesive manufacturer published values for hollow, grouted and solid masonry
• See related: The Anchor Types and What Each Needs From the Base Material
• See related: How to Choose an Anchor for What You Are Hanging