Will sealing my brick stop it spalling?

Not by itself, and the wrong sealer makes it worse. Brick walls get wet and need to dry. A penetrating repellent on sound masonry sheds driving rain while still letting vapor out, which helps. A film-forming coating seals the face, water that entered from a joint or a sill cannot leave, and the next hard freeze pushes the brick face off from behind.

How long does a repellent last?

Most penetrating silane and siloxane treatments are quoted at seven to ten years on vertical masonry, less on a chimney or a parapet that takes weather on several faces. It is a maintenance item rather than a permanent fix. The manufacturer's data sheet for the specific product will give the expected service life and we put that on your estimate.

Can you seal a wall right after tuckpointing?

No. Fresh mortar needs to cure and dry before anything goes over it, and 28 days is the usual minimum. Sealing too early traps mix water in the joint and can leave a blotchy finish. Most of our customers have the pointing done in spring or summer and the repellent applied later in the same season once the wall is properly dry.

What about a parapet wall?

A parapet is the most exposed masonry on a flat roofed building, wet on both faces and open on top. Repellent alone will not save one. It needs a coping that overhangs both sides with a drip, sound pointing on both faces, and correct flashing where the roof membrane turns up. Many parapets in the city have lost their original stone or terra cotta coping.

Is a clear sealer visible?

A good penetrating repellent should leave the brick looking the way it does dry, with no sheen. Some products slightly deepen the color. That is why we put a test patch on an inconspicuous area, let it dry fully, and have you look at it in daylight before the whole elevation is treated.

We do not recommend painting old brick and we will talk you out of it if we can. Paint on soft common brick holds moisture in the wall, blisters, and becomes a permanent maintenance cost, because stripping it later is expensive and can damage the face. If a wall has already been painted, breathable mineral coatings are a better maintenance path than another coat of acrylic.

Masonry Waterproofing and Sealing in St. Louis | Gateway Brick & Tuckpointing

Masonry Waterproofing and Sealing in St. Louis

Breathable masonry water repellent in St. Louis runs $1.75 to $4.50 per square foot, and it only belongs on a wall that is already sound. Sealing a wall with open joints or spalled brick traps water inside the masonry and makes the damage worse. We repoint and correct the details first, let the mortar cure, then treat the wall if it still needs it.

Signs you need this

Damp patches on interior plaster that follow heavy driving rain

A parapet or freestanding wall with no coping over the top of it

Stone or cast sills that have lost their slope and hold water

Brick that stays visibly dark for days after rain on one elevation

A previous sealer that has gone patchy, glossy or milky

Efflorescence returning on the same area every spring

The honest version of masonry sealing

Sealers are sold hard in this trade and they are the easiest thing to get wrong. A brick wall is not a raincoat. It is a porous system that takes water in during a storm and gives it back to the air afterward. Everything you put on it either helps that cycle or interferes with it. The useful products are penetrating repellents based on silanes or siloxanes, which soak into the masonry, line the pores and shed liquid water while staying open to vapor. The damaging ones are film formers that bridge the surface and stop the wall drying outward.

We turn down sealing work regularly. If your joints are open, if brick faces are spalling, if the crown is cracked or the sill is dumping water into the wall, a repellent will take your money and hide the problem for a season. The order is always repair, cure, then treat.

Details that do more than any product

Most water gets into masonry at the same handful of places, and all of them are cheaper to fix than a wet wall is to live with.

Caps and copings. Any masonry with a flat open top is a funnel. Parapets, garden walls, porch cheek walls and chimney crowns all need a cap that overhangs and drips.

Sills. A stone or cast sill is supposed to slope away and carry a drip on the underside. Decades of paint, a lost slope from settlement or a cracked sill all reverse that and feed water straight into the wall and into the lintel below.

Flashing and gutters. A downspout that spills at the wall, or a gutter that overflows behind the fascia, will beat any sealer on the market.

Grade. Soil built up above the damp course or against soft brick keeps that brick saturated all year.

Where treatment genuinely earns its keep

There are walls in St. Louis that stay wet no matter how good the pointing is. A tall west elevation with no overhang on a corner lot takes driving rain that would soak any masonry. A chimney above a roof is exposed on five surfaces. A parapet on a storefront is wet on both faces. On those, a breathable repellent applied to sound, cured masonry meaningfully reduces how much water the wall absorbs and how much it has to deal with each winter.

We record the product name and the data sheet on your estimate so you know exactly what went on your building and when it will want renewing. That matters if the building is in a local historic district, where the Cultural Resources Office may want the product identified before work starts, and it matters at resale.

How the work runs

Find the actual entry point

Wind driven rain, a failed joint, a leaking gutter and a missing coping all produce a damp wall. We work out which one you have before suggesting any product, because a repellent fixes only one of them.

Repair before you treat

Pointing, brick replacement, sill and cap work all come first. Repellent applied over failed masonry seals water into the wall and can accelerate spalling through a winter.

Choose a breathable product

We use penetrating silane and siloxane repellents that let water vapor out while shedding liquid water. Film-forming acrylics and most gloss sealers do the opposite on old brick.

Test, then apply and cure

A test patch goes on first so you can see the finished look when dry. Mortar cures at least 28 days before treatment, and the wall has to be dry and above the product's minimum temperature.

What it typically costs

Job	Typical range
Masonry water repellent, per sq ft Breathable penetrating repellent on sound masonry, applied after any pointing has cured	$1.75 to $4.50 per sq ft
Chimney stack treatment Above-roof masonry treated on all four faces. Access drives the price	$300 to $850
Parapet coping, installed Stone, cast or metal coping over an open parapet, with a drip on both sides	$55 to $140 per linear ft
Sill repair or replacement Restoring the slope and the drip so the sill throws water clear of the wall	$450 to $1,600 per opening
Removing a failed film sealer Where a previous gloss or acrylic coating has to come off before the wall can breathe again	$3 to $9 per sq ft

Typical ranges for St. Louis and the surrounding area , reviewed September 2026. Every quote is written and fixed before work starts.