Efflorescence: what a fix costs

Efflorescence is a white, powdery crust of mineral salts that forms on masonry as water moves through the material and evaporates at the surface. Fixing it usually costs $175 to $510 on a 300 sq ft patio if the cause is surface salts and a good cleaner, and $1,200 to $2,400 if the moisture is coming from a failed base and the patio has to come apart. The difference between those two bills is diagnosis, not effort.

What Efflorescence Actually Is

The salts are already in the cement, the sand, or the ground water. Water dissolves them, carries them to the surface, and leaves them behind when it evaporates. The crust is a symptom. The water is the problem.

That distinction explains why the same patio blooms every spring. A cleaner removes what is on the surface, and if the moisture path is still open, the salt returns within a season or two. Sometimes it looks like efflorescence and is actually a sealer haze, a poor-quality sealer that went down over damp pavers, or a lime bloom from mortar work nearby. Those have different fixes.

Why It Comes Back After Cleaning

Four moisture paths feed it. Water can rise from the subgrade through the base and the bedding sand, which is a base drainage problem. It can enter from the surface through open joints and porous units. It can come from a sprinkler hitting the same wall or patio edge every morning. It can come from new concrete or mortar curing nearby, which is a one-time bloom that resolves on its own.

In paver patios, the first path is the one that matters. Sand-set units over a base that holds water stay damp from below, and the sun pulls the moisture up through the joints. A patio that blooms only along one edge, or only at the low corner where water pools, is telling you where the water is.

Cleaning Cost: Yourself Versus a Crew

The cleaner is the cheap part. Most efflorescence removers are mild acid blends, and they are unforgiving on travertine, limestone, and anything with a polished or honed finish. Read the label for the specific stone before you buy, and test on one paver in a corner.

Pressure washing deserves a warning of its own. It can drive water deeper into the assembly, strip the joint sand, and etch soft stone. If the patio already has a moisture problem, blasting it makes the problem worse.

The Arithmetic on a 300 sq ft Patio

A DIY clean with one gallon of remover and a pump sprayer:

• Cleaner: $25 to $60
• Sprayer and brush: $20 to $40, one-time
• Total: $45 to $100 for 300 sq ft

A professional wash and treat at $0.50 to $1.50 per sq ft:

• 300 × $0.50 = $150
• 300 × $1.50 = $450

Add sealing afterward at $1 to $3 per sq ft:

• 300 × $1 = $300
• 300 × $3 = $900

So a clean-and-seal on 300 sq ft runs $175 to $510 doing the washing yourself, or $450 to $1,350 with a crew. That is the cosmetic bill. It is not the whole story, and it is why quotes for efflorescence vary by a factor of five.

When the Fix Is Not Cleaning

If the bloom keeps returning in the same band, or the joints are soft and the pavers rock, the base is the source. Base repair runs $4 to $8 per sq ft, so 300 sq ft is $1,200 to $2,400. That is four to ten times the cleaning bill, and it is the only version that stops the cycle. paver base preparation covers what a proper rebuild involves.

The tell is physical. Probe the damp area with a screwdriver. Soft, spongy base under a rocking paver means water has been sitting there, and no amount of acid will change that. Efflorescence on a structurally sound patio is cosmetic. Efflorescence over a failed base is a symptom of a repair that is already due.

Sealing: Price and Timing

Sealing does not cure efflorescence. A penetrating sealer slows the movement of water through the surface, which slows the salt migration, and that is worth $1 to $3 per sq ft on a patio that blooms lightly. It is a waste of money on a patio with a wet base, because the water will find the joints regardless.

Timing matters as much as product. Seal when the pavers are dry, the efflorescence has stopped, and the forecast is clear for two days. Sealing over an active bloom traps the salt under the film and produces a cloudy mess that has to be stripped.

Efflorescence Versus Haze Versus Staining

Efflorescence is white, powdery, and usually comes off with a brush and water. Sealer haze is a milky film that follows the squeegee lines and does not brush away; it needs a stripper. Hard-water staining is a chalky ring at the edges where sprinklers land, and it responds to a different cleaner. Rust is orange and comes from a nail, a chair leg, or fertilizer.

Get the diagnosis right before buying anything. A $30 bottle of the wrong product and a Saturday is a more expensive mistake than it looks, and the wrong acid on travertine can etch a visible patch into the surface.

A Four-Step Plan

1. Wash a small test patch with water and a stiff brush, and see whether the white comes off. If it does, it is surface salt.
2. Dry the patch and watch for 48 hours. If the bloom returns immediately, water is still moving.
3. Probe the damp area for soft base and check where the patio drains. Rocking pavers or a low corner change the plan from cleaning to repair.
4. Clean, let the surface dry fully, then seal at $1 to $3 per sq ft if the patio is otherwise sound.

Budget the cleaning at $175 to $510 on 300 sq ft, and keep the base repair number — $1,200 to $2,400 — in mind before authorizing a second round of cleaning that will not hold. For the moisture side of the problem, drainage pooling signs covers what standing water is telling you, and paver sealing cost covers the sealer arithmetic in more detail. If the surface has already spalled, paver repair cost is the next number to check.