TL;DR: Soluble salts like chlorides and sulfates are invisible contaminants that abrasive blasting alone often fails to remove, and they’re a leading cause of premature coating blistering and corrosion. In Central Florida’s humid, salt-penetrated climate, testing surfaces before and after blasting with methods like the Bresle test is a low-cost step that protects the entire coating investment.
A freshly blasted steel surface can look perfect and still be contaminated. Chlorides, sulfates, and nitrates left behind from prior corrosion, de-icing residue, industrial fallout, or coastal air don’t show up to the naked eye — but they will show up later, as blisters, rust bleed, and disbonded coating.
That’s what soluble salt testing is for. It’s a field test performed before and after abrasive blasting to confirm a substrate is clean enough, at a measurable level, to hold a protective coating system for its intended service life.
What Soluble Salt Testing Actually Measures
Soluble salts, including chlorides, sulfates, and nitrates, left on the surface prior to coating application can lead to osmotic blistering, corrosion, and coating failures.
These contaminants aren’t dirt or rust scale you can brush off — they’re ionic residues embedded in pits, porosity, and surface roughness.
There are two widely accepted techniques for testing salt contamination on steel: specific ion detection and conductivity. Specific ion detection will determine whether chlorides, sulfates, nitrates, and ferrous ions are present and in what quantity, while conductivity will only establish the presence of some type of water-soluble salt that is causing the electrical conductivity of water to increase.
The most widely used field method is the Bresle patch test.
The test was developed to measure soluble salt concentration on steel surfaces prior to blasting cleaning and coating.
A small chamber is sealed to the surface, filled with a measured volume of deionized water, agitated to dissolve any residual salts, then extracted and measured with a conductivity meter.
Why This Matters So Much in Central Florida
Florida’s atmosphere is uniquely hard on bare and recoated steel. Chloride isn’t just a coastal problem here — it travels. Research on U.S. salt deposition patterns has found that
Florida receives the highest rate of salt penetration in the USA, even up to 100 miles inland
. That means facilities in Orlando, Ocala, DeLand, Deltona, Clermont, and St. Cloud are not exempt from chloride contamination just because they’re inland — tanks, structural steel, and equipment across Central Florida can carry meaningful salt residue even far from the coast.
Layer that chloride exposure on top of Central Florida’s humidity and heat cycles, and you get conditions that are almost engineered to activate any salt left behind after blasting. Hygroscopic salts pull moisture out of the air, forming a microscopic electrolyte film under the coating — exactly the mechanism that drives osmotic blistering and underfilm corrosion. For more on how this plays out on exposed steel, see our breakdown of salt spray corrosion on coastal steel in Central Florida.
Why Blasting Alone Doesn’t Solve the Problem
It’s a common assumption that abrasive blasting removes everything, including salts. It doesn’t, reliably.
Because common surface preparation methods, such as abrasive blasting or power-tool cleaning, do not reliably remove soluble salts, verification prior to coating is often critical to long-term coating performance.
Worse, blasting can actually spread contamination if it’s not managed.
If soluble salts on the surface are not sufficiently removed prior to abrasive blast cleaning, recycled abrasive media can become contaminated — which is why SSPC-AB 2 requires that recycled abrasive be routinely tested for water-soluble contaminants, with a maximum concentration of 1,000 µS/cm.
Dirty abrasive just redeposits salt across every surface it touches afterward.
The Standards That Govern Salt Testing
Soluble salt testing is referenced across the major surface preparation standards used on commercial and municipal coating specifications:
- SSPC-Guide 15 —
Field Methods for Retrieval and Analysis of Soluble Salts on Steel and Other Nonporous Surfaces
, covering swab, sleeve, and patch extraction techniques. - SSPC-Guide 24 —
provides guidelines for testing soluble salt contamination on new steel surfaces before applying protective coatings, outlining the scope, definitions, and necessary testing frequencies and locations for various steel components. - ISO 8502 (parts 2, 5, 6, 9) — the international standard series for assessing surface cleanliness and soluble salt levels, including the Bresle method.
- SSPC-AB 2 — governs abrasive cleanliness, requiring conductivity testing of recycled blast media.
There is no industry consensus standard defining an acceptable soluble salt level
for every situation — allowable thresholds depend on the coating system, immersion versus atmospheric service, and the owner’s specification. That’s why
specification writers are advised to check the coating manufacturer’s technical data sheet, since the allowable salt level is dependent on the expected service life for the specified coating in a particular environment.
Pros and Cons of Soluble Salt Testing
Advantages
- Catches a failure mode that’s completely invisible during a standard visual inspection.
- Relatively low cost per test compared to the cost of coating rework or early recoat.
- Gives facility owners and specifiers objective, documented pass/fail data for acceptance.
- Confirms whether pre-blast cleaning or additional rinsing steps are needed before coating proceeds.
Limitations
- Conductivity testing alone can’t identify which specific ion is present, only that something dissolved is there.
- Results can be affected by temperature, humidity, and technique if not standardized.
- No universal pass/fail number exists — thresholds must be tied to the coating manufacturer’s requirements and the project spec.
- Testing adds a step and modest cost to the schedule, which some bidders are tempted to skip.
When Soluble Salt Testing Matters Most
Not every project needs the same rigor, but certain conditions make testing close to non-negotiable:
- Immersion service — water tanks, towers, and tank interiors where even low salt levels can cause rapid blistering under constant wetting.
- Previously corroded steel — pitted structural steel, pipelines, and older tanks almost always carry embedded chloride in the pits themselves.
- Structures near any salt exposure — airport ramps, hangar steel, and equipment exposed to deicing chemicals or coastal air drift.
- High-value, long-service coatings — when the owner is specifying a 15-20 year coating system, verifying a clean substrate protects that investment from day one.
- Municipal and DOT specifications — many public agency specs now explicitly call out soluble salt testing as an acceptance criterion before coating sign-off.
This same emphasis on verified surface readiness applies to related inspection steps on a coatings project, including anchor profile measurement and holiday testing after the coating is applied. Salt testing, profile measurement, and holiday testing form a three-point quality chain: clean substrate, correct texture, and a continuous film.
What This Looks Like on a Real Project
On a typical tank or structural steel job in our service area, testing happens at two points. First, a baseline check on the as-found surface identifies whether extra pre-cleaning (fresh water rinse, detergent wash) is needed before blasting even starts. Second, after blasting and before any primer goes on, spot checks confirm the surface meets the salt threshold specified for that coating system.
For galvanized components or dissimilar-metal assemblies, salt testing is paired with the right prep sequence — see our guide on preparing galvanized steel before painting for how that process differs from bare carbon steel.
The Bottom Line for Facility Owners and Specifiers
Soluble salt testing is a small line item compared to the cost of a coating system failing years ahead of schedule. In a climate where Florida sees some of the deepest chloride penetration in the country, skipping this verification step on a tank, hangar, pipeline, or structural steel project is a gamble most owners don’t need to take.
Southern Sandblasting & Painting LLC builds soluble salt testing into surface preparation scopes for municipal, airport, pipeline, and commercial coating projects across Orlando and Central Florida, including Maitland, Winter Park, Windermere, Oviedo, Altamonte Springs, and surrounding communities, so coating systems perform for their full intended service life.
Recommended Reads
- What Is Holiday Testing and Why It Matters for Industrial Protective Coatings
- How to Properly Prepare Galvanized Steel Surfaces Before Painting
- Salt Spray Corrosion on Coastal Steel: How It Destroys Structures in Central Florida — and
