Coal tar epoxy has a reputation as a forgiving coating, and compared to a lot of high-performance linings, it is. That reputation leads some crews to treat the prep like an afterthought — a quick commercial blast, or a power tool cleanup on “new” steel.
The manufacturer doesn’t see it that way. Carboline’s product data sheet for Bitumastic 300M spells out the surface prep, and it’s the same level of prep you’d give most immersion-grade epoxies. Here’s what the spec says and what it means in the field.
The Spec, Line by Line
For steel, Bitumastic 300M calls for:
- SSPC-SP 1 Solvent Cleaning — remove all oil, grease, dirt, and contaminants before blasting.
- SSPC-SP 10 / NACE No. 2 Near-White Metal Blast Cleaning.
- A 2.0 to 3.0 mil (50–75 micron) dense, angular anchor profile.
Then it goes on at 16 to 24 mils dry per coat, self-priming, in one or two coats.
Each of those steps is doing a job. Skip one and the coating is working against you from day one.
Step 1: SSPC-SP 1 Before You Blast
Abrasive blasting doesn’t remove oil. It spreads it. Blast over a greasy flange or a pipe end with cutting oil on it and you drive the contamination into the profile, then coat right over it. The coating looks fine and fails in patches months later.
SP 1 means solvent or detergent cleaning of anything oily before the blast. On new pipe and fabricated steel, look for:
- Cutting and threading oil at pipe ends and fittings
- Mill oil and preservative coatings from the manufacturer
- Marking crayon, paint stick, and layout marks
- Grease from handling equipment and forklift forks
A water-break test (wet the surface and look for water beading) is a quick check that oil is gone.
Step 2: SSPC-SP 10 Near-White Blast
SP 10 means the blasted surface is free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, and corrosion products. The only thing allowed is light staining — shadows, streaks, or slight discoloration from rust or mill scale — on no more than 5% of each 9-square-inch area.
In plain terms: gray, uniform steel with an occasional shadow. No intact mill scale. No rust in the pits.
Why SP 10 instead of a cheaper SP 6 commercial blast?
Mill scale. SP 6 allows up to one-third of the surface to have staining and doesn’t require removing all the tightly adhered material. Mill scale is the big problem. It’s a brittle oxide layer that’s bonded to the steel but cracks and pops loose as the steel expands, contracts, and corrodes underneath. Coal tar epoxy bonded to mill scale is only as well bonded as the mill scale is. When the scale lets go, the coating goes with it.
Immersion and burial. Bitumastic 300M is used in immersion and buried service where water sits against the coating full time. Any weak spot in adhesion becomes a blister, then an undercut, then a corrosion site you can’t see until someone digs it up or drains the tank.
Cathodic protection. Buried and submerged steel coated with coal tar epoxy is often cathodically protected. Poor adhesion makes cathodic disbondment — coating lifting away from the steel around a defect — much worse.
Step 3: A 2–3 Mil Angular Profile
The profile is the texture the blast cuts into the steel: microscopic peaks and valleys that the coating locks into. For Bitumastic 300M, the target is 2.0 to 3.0 mils, and it needs to be angular, not peened.
- Too shallow (under 2 mils): not enough mechanical grip for a 16–24 mil film. Thick coatings shrink as they cure and put stress on the bond. A shallow profile can’t hold it.
- Too deep (well over 3 mils): peaks can poke through thinner areas of the film, and you use more coating filling valleys.
- Rounded (from steel shot or worn media): lower surface area and weaker grip than an angular profile at the same depth.
Getting 2–3 mils consistently comes down to abrasive choice and blast pressure. A properly sized angular abrasive — steel grit, coal slag, or garnet — at the right nozzle pressure will get there. Whatever’s left on the truck from the last job might not. We cover abrasive options in Abrasive Selection for Silica-Free Industrial Sandblasting.
Profile should be measured, not eyeballed — replica tape per ASTM D4417 Method C or a profile depth gauge — and written down. More on why in Surface Profile and Coating Adhesion.
After the Blast: Clean, Dry, and Coat Fast
Remove dust and spent abrasive. Blow down with clean, dry, oil-free air and vacuum where needed. Dust left on the surface is a bond breaker.
Watch the dew point. Coatings shouldn’t be applied unless the steel temperature is at least 5°F above the dew point. In Michigan, early mornings, pipe that’s been sitting on cold ground, and steel inside unheated buildings are all common dew point traps.
Coat before flash rust. Freshly blasted steel starts to rust quickly in humid conditions. If the surface has flash rusted or it’s been long enough that contamination has settled on it, it needs to be re-blasted. Blast only what the coating crew can cover that shift.
Check soluble salts on older or exposed steel. Pipe and steel that’s been stored near road salt, near the coast, or in chemical service can carry chlorides that blasting alone won’t remove. Salts trapped under an immersion coating pull water through the film and cause blistering.
Coating Application Notes
A few things to watch once the prep is done, all of which are covered in the product data sheet:
- Film build. 16–24 mils DFT per coat. Measure wet film as you go and dry film after cure.
- Recoat windows. Coal tar epoxies have limited recoat windows. If you’re applying two coats and miss the window, the second coat may not bond to the first without surface prep between coats. Follow the data sheet.
- Holiday testing. For immersion and buried service, spark test the cured coating and repair pinholes before the steel goes into service or into the ground.
Why Prep Is Where the Money Is
A gallon of coal tar epoxy is one of the cheapest line items on the job. Excavating a failed buried pipe or draining and re-lining a tank is one of the most expensive. The prep is what decides which one you end up paying for.
Blasting Jack blasts steel to SSPC-SP 10 and SP 5 with documented anchor profiles for coal tar epoxy, immersion linings, and buried-service coatings across Michigan — shop, yard, or field. Contact us to get your next coating job prepped to spec.