If you own anything that sits over water in Columbia County, you already know how this goes. The dock frame on the Suwannee looked fine in March. By August the bolt heads are weeping orange and the paint on the boat lift is coming off in sheets you can peel with a thumbnail. Marine surface preparation is the difference between a coating that holds for eight or ten years and one that fails in two, and around here almost every failure we get called out to fix traces back to prep that got rushed. Not cheap paint. Not bad luck. Prep.
Here is the honest part most people skip: on waterfront steel, the blasting is the easy half. Knowing what to wash off first, what profile to leave behind, and how fast you have to get primer on it — that is the job.
1. Marine surface preparation starts with a wash and a salt test, not a nozzle
Steel that lives over water carries a film of soluble salts. On the coast that is chloride off the spray. Inland on the Santa Fe and the Suwannee it is more often sulfates, fertilizer runoff, and whatever the river leaves behind when it drops back down after a summer rise. You cannot see any of it. You can blast a piece of dock steel to bright metal, look at it in the sun, and be proud of it — and still have salt sitting in the bottom of every pit.
Why that matters: salt pulls moisture straight through a coating film. The paint looks perfect for a year, then blisters from underneath. We wash first with fresh water and a detergent rated for salt removal, and on anything that has been in a splash zone we test before we coat. If the reading is high, it gets washed again. That step costs a little time and saves the whole job.
Anybody who skips straight to the blast pot on waterfront steel is doing you a disservice, whether they know it or not.
2. Match the media to the metal — docks are rarely all one thing
Walk a typical Columbia County dock and you will find three or four different metals bolted to each other. Galvanized pipe pilings. Structural steel stringers. An aluminum gangway. Stainless fasteners. A boat lift with a painted steel I-beam and aluminum cradle arms. They do not all want the same abrasive.
- Structural steel takes a hard angular media — garnet or slag — because it needs a real anchor profile to hold a heavy marine coating.
- Galvanized needs a light sweep only. Blast it aggressively and you strip the zinc you paid for, and zinc is the only thing keeping that piling alive.
- Aluminum wants a softer media and a lighter touch. Too much pressure and you dish the panel or drive iron particles into the surface, which starts its own corrosion problem later.
This is where metal sandblasting done by someone who reads the surface first earns its keep. We change media and pressure as we move down the structure. Same price — we pick by what is in front of the nozzle, never by the invoice.
3. Blast to the right SSPC grade, not the shiniest one
There is a real temptation to blast everything to white metal because it photographs beautifully. It is also usually overkill, and on a dock it can be a waste of your money.
The grades we work to most on waterfront steel:
- SP 10 / near-white — for anything in the splash zone or going under water. Pilings, lower bracing, seawall tiebacks. This is where you want it near-perfect, because you will not get another easy shot at it.
- SP 6 / commercial blast — the honest workhorse for handrails, stringers, gangway frames, and lift towers above the splash line. Plenty of tooth, plenty of life, less time on the clock.
- SP 7 / brush-off — for galvanized and for sound existing coatings that just need a key for a topcoat.
Profile depth matters as much as cleanliness. Most heavy marine primers want somewhere around a 2 to 3 mil anchor pattern. Too shallow and the coating has nothing to grip. Too deep and the peaks of the profile poke through a thin film and rust right through the paint in little brown freckles. If you want to read the standards yourself, SSPC publishes the surface preparation specifications the whole industry works from.
4. Flash rust beats you faster over water than anywhere else
Bare steel in North Florida starts flash rusting before supper. Bare steel standing three feet over a river, in August, with the humidity sitting where it sits, can start hazing in under an hour.
So we work in sections. Blast a run, clean it, prime it, then move down the dock. Nobody on our crew blasts a whole structure on Tuesday and comes back with paint on Thursday. If the weather turns and we cannot coat, we stop blasting — because bare steel sitting overnight in river air has to be reblasted, and that is on us, not on you.
Dew point is the other one people miss. If the steel is colder than the dew point, there is moisture on it whether you can see it or not, and primer over that will not stick. Early mornings on the water are the worst offender for this. Sometimes the right call is to wait two hours. We would rather tell you that than paint something we know is going to fail.
5. Coat by zone — a dock is three different environments
One coating system for the whole structure is the single most common mistake we see on do-it-yourself dock jobs. A piling lives in three worlds at once:
- Submerged — constant wet, no oxygen cycling, needs a thick-film system built for immersion.
- Splash and tidal / fluctuating waterline — wet, dry, wet, dry, plus abrasion from debris and boat hulls. This is where steel dies first, every single time.
- Atmospheric — sun, rain, and UV. Wants a primer plus a topcoat with real UV resistance, or the color chalks off and takes the film thickness with it.
We blast and coat with the same crew on the same trip, which is the main reason we can hit the recoat windows the data sheets actually call for. Our painting and coating work is not a separate contractor who shows up next week — it is the same people who did the prep and know exactly what is under the paint.
6. Seawall caps, concrete, and the stuff that is not steel
Plenty of waterfront work around Lake City is not steel at all. Concrete seawall caps, boat ramp aprons, spalling where the rebar has started to swell and push the face off. Concrete gets prepped differently: you are opening the surface to a consistent texture and getting rid of laitance, old sealer, and algae, not cutting a profile into metal.
If the rebar is exposed and rusting, blasting alone does not fix it — the steel has to be cleaned to bright and treated before any patch goes on, or the rust keeps expanding under the repair and pops it off in a year. We will tell you straight if what you have is a coating problem or a structural one. If it is structural, you want a concrete contractor, and we will say so. Concrete sandblasting is the right tool for surface prep and coating removal, not for a failing cap.
Containment over water is not optional
Spent abrasive and old paint chips do not belong in the Suwannee, the Santa Fe, or Alligator Lake. If the existing coating is old enough to be lead-bearing — and on 1970s and 1980s dock and bridge steel it often is — containment and worker protection are legal requirements, not preferences. OSHA lays out the abrasive blasting rules plainly, and they exist for good reason.
On over-water work we tarp and skirt below the work area and catch what comes off. When containment would be difficult or the coating is fragile, green and dustless blasting is sometimes the better answer because the water knocks the dust down. Here is the trade-off, honestly: it makes a wet slurry mess you have to rinse off, and the surface has to be dried and checked before primer. It trades one problem for another. We will tell you which one your job wants.
When you should not call us
If you have a small aluminum gangway with a little oxidation and no coating on it, leave it alone. Aluminum forms its own oxide layer and that layer is doing a job. If you have surface rust on a handrail and a wire brush and a Saturday afternoon will handle it, that is a wire brush and a Saturday afternoon, not a blast rig.
And if the steel is section-loss gone — you can put a screwdriver through it — blasting will only prove it. That is a welder and new steel, and no amount of paint fixes it.
Where we are worth calling: a lift or dock frame with widespread rust, a structure you want to get another decade out of, anything where you have already repainted once and watched it fail, or a job where you want the prep, the coating, and the responsibility for the outcome all resting with one crew.
We cover Lake City, Fort White, Branford, Live Oak, White Springs, Wellborn, and the river and lake properties in between. The rig comes to your dock — you do not haul anything anywhere.
Need sandblasting in Lake City or nearby? Call (386) 400-1904 for a free on-site estimate. You will reach someone who actually does the work.