Should I seal the brick on my house in Michigan?

Should you seal the brick on your house?

Most homeowners should not seal the brick on their house. The Brick Industry Association (BIA), the trade group for clay brick makers, addresses this question in Technical Note 6A on colorless coatings for brick masonry, published in August 2008 and still the edition BIA publishes. Its summary says a water repellent is not necessary for brick under normal exposure when materials, detailing, construction and maintenance are sound. The same note says coatings are not recommended on newly built brick veneer or cavity walls.

A brick sealer is any clear coating brushed or sprayed onto a brick wall to keep water out. The question usually comes up right after a wash, when the wall looks clean and the owner wants to keep it that way. A clean wall is a good time to look the brick over, but a coating is rarely the next step. On most Michigan houses the better answer is to find where water is getting in, fix it, and leave the brick uncoated.

Why doesn't brick need a sealer under normal exposure?

Brick does not need a sealer under normal exposure because a brick veneer wall is built to handle water without one. Many brick houses, including mid-century ranches, have brick veneer: a single layer of brick tied to the frame wall, with an air space behind it. In a working veneer wall, rain that soaks into the brick or gets past it runs down the back of the veneer to flashing and weep openings near the bottom of the wall and drains out. On some older houses the weeps are blocked with mortar or the flashing is damaged or missing, which is why TN 6A lists both among the repairs to consider, so check the base of the wall before blaming the brick.

A clear coating does little against the way water usually gets into a brick wall. According to TN 6A, most leaks come through cracks and gaps between brick and mortar or at joints with windows, sills and other materials, not through the face of sound brick. Water repellents cannot make up for failed sills, caps and copings or for mortar joints that were never filled. Penetrating repellents seldom stop water through cracks wider than 0.02 inch (0.5 mm), and they do little against wind-driven rain.

What goes wrong when brick is sealed with the wrong product?

Brick sealed with the wrong product can cloud over, hold salts inside the wall and lose its face. A brick wall takes on water and gives it back as vapor through its face. A coating that slows that drying leaves the water inside longer. Moisture trapped behind some films, such as stearates and waxes, turns the coating cloudy or milky white, which the BIA calls clouding. TN 6A adds that clouding from a reapplied coating may be difficult or impossible to remove.

Salt damage is the other risk when brick is sealed with the wrong product. Brick and mortar carry soluble salts, and water moving through the wall carries them toward the face. On uncoated brick they show up as the white bloom of efflorescence, which our efflorescence guide covers in detail; a hard white crust that will not wash off is a different deposit, explained in our post on white crust on brick. Under a film, or under a repellent that breathes poorly, those salts can be trapped behind the coating. As they crystallize they grow and press outward with enough force to break off pieces of the brick face, which is called spalling.

Why are film-forming sealers a problem in freeze-thaw climates like Michigan's?

Film-forming sealers are a problem in freeze-thaw climates because they keep water in brick that is about to freeze. A film former is a coating that sits on the surface as a layer: acrylics, urethanes, stearates and wax products are the common types. TN 6A puts the rule in one line: do not apply film-forming coatings to brickwork located in freeze-thaw environments.

Southeast Michigan winters swing above and below freezing again and again between late fall and spring. Water that cannot dry out of the brick freezes and expands in the pores near the face. Each cycle adds stress, and the damage shows as flaking, popped faces and crumbling edges, often low on the wall or under a leaky gutter. Film formers also tend to leave a sheen or wet look, and the BIA notes that an unwanted gloss can signal a poorly applied or poorly chosen coating.

What is a breathable water repellent, and when does one make sense?

A breathable water repellent is a penetrating product that soaks into the brick and lines the pores without forming a film on top. TN 6A says penetrants typically reach up to 3/8 inch (10 mm) deep. They make the pore walls shed liquid water while vapor can still escape. For exterior brick walls, the BIA recommends siloxanes, or siloxane and silane blends, with a water vapor permeability of 0.98 or higher by the ASTM E96 test, a level BIA says still lets the wall's natural evaporation take place.

A breathable water repellent makes sense on brick that still absorbs too much water after repairs, such as a wall of soft, thirsty brick on an exposed side. The BIA also asks for a product with at least five years of proven performance on similar brick in a similar climate, and suggests asking the brick manufacturer first when the brick type is known. Siloxanes bond to glass, so windows need protection during application.

A breathable water repellent goes on a clean, dry wall within the temperature range on the product label, which the BIA notes is typically above 40°F and below 100°F, on a calm day. The waiting time after washing comes from the product label and the moisture level it calls for, checked at several spots on the wall. A test area of at least 10 square feet, left to cure and then checked for color change, comes before the full wall. That cleaning step is part of our house washing service. BIA Technical Note 20 sets the limit for washing brick at 400 psi at the nozzle unless the brick maker permits more, and older or soft joints need a gentler approach, as our post on whether pressure washing damages brick explains. Limestone or cast-stone sills on the same wall have their own rules, covered in our limestone sills guide.

What has to be fixed before any brick is coated?

The water problems in the wall have to be fixed before any brick is coated, because a coating over an active leak traps the water in. TN 6A lists the common repairs to finish first:

1. Replace failed sealant at windows, sills, copings, expansion joints and where brick meets other materials.
2. Repoint mortar joints that are cracked, crumbling or never fully filled.
3. Replace brick with spalled faces or cracks through the face.
4. Close separations between brick and mortar.
5. Clear blocked weeps and replace damaged or missing flashing where needed.

After the repairs, the BIA advises waiting several months to see whether a water repellent is still needed, because repairs often solve the problem by themselves. Freshly repointed mortar and new sealant need at least 72 hours of cure before any coating. On a new house, the BIA prefers a one-year wait so first-year efflorescence is not sealed in. Outside the wall, the usual Michigan culprits are an overflowing gutter, a downspout dumping at the foundation and a sprinkler hitting brick. Our post on sprinkler rust and hard water on brick covers re-aiming heads.

Are chimneys and parapets exceptions to the no-sealer rule?

Chimneys and parapets are the main exceptions where a clear water repellent can help on a house. These parts stick up into the weather on every side, take wind-driven rain, and get water running down from the crown or cap above. TN 6A says a clear repellent can sometimes reduce water problems on them, especially in very wet climates and on sloped or flat ledges where water and snow sit.

A chimney still needs the basics before any repellent goes on: a crown without cracks, flashing that seals at the roof and sound mortar joints. A cracked crown sends water straight into the brick below, and no repellent stops that. The same breathable siloxane rules apply to a chimney, and film-forming products stay off it.

How do brick coating types compare?

Brick coating types compare most clearly on breathability and life span, which come from the BIA table of typical properties. Most coatings need reapplying every five to 15 years, and some last far less.

The table shows why BIA steers exterior walls toward siloxanes and silanes: they are the types that pair very good vapor transmission with a life of 10 years or more. A brick wall that looks dirty or green needs cleaning, not a coating. For brick washing, Macomb Power Washing Solutions provides an itemized written quote within 24 hours and charges no travel fee.