Three coating families cover most buried and submerged steel pipe: coal tar epoxy, fusion-bonded epoxy (FBE), and asphalt or bituminous mastics. People lump them together as “the black stuff” or “the green stuff,” but they behave very differently in the ground, in the field, and on the spec sheet.
Here’s how they compare, where each one makes sense, and what each one needs from the surface prep.
Quick Comparison
| Coal Tar Epoxy | Fusion-Bonded Epoxy (FBE) | Asphalt / Bituminous Mastic | |
|---|---|---|---|
| Example | Carboline Bitumastic 300M | Shop-applied powder epoxy (AWWA C213) | Asphalt mastic; some NSF 61 asphalt coatings |
| Where it’s applied | Shop or field | Shop only (field joints separately) | Shop or field |
| Typical thickness | 16–24 mils per coat | Thin film, typically 12–16 mils | Thick, varies widely |
| Potable water interior | No | Yes, with NSF 61 product | Only if NSF 61 certified asphalt |
| UV / sunlight | Poor — below grade only | Chalks; needs protection long-term | Poor |
| Handling damage | Tolerant | Brittle, chips in handling | Soft, gouges easily |
| Cathodic protection | Compatible | Excellent disbondment resistance | Compatible |
| Surface prep | SSPC-SP 10, 2–3 mil profile | Near-white or white blast, controlled profile, heat | Varies — commercial blast or better |
Coal Tar Epoxy
Coal tar epoxy blends coal tar into a two-part epoxy. The epoxy provides adhesion and toughness, and the coal tar makes it more water-resistant and flexible. Bitumastic 300M is the best-known product.
Strengths:
- Very thick in one or two coats, so it covers edges, welds, and pitting well
- Excellent resistance to water, soil chemicals, and immersion
- Forgiving of field conditions compared to thin-film systems
- Can be applied in the shop or the field, so field joints and repairs match the main coating
- Low material cost
Weaknesses:
- Coal tar is a known carcinogen. It’s not NSF 61, can’t be used in potable water service, and some owners ban it outright
- Breaks down in sunlight
- Hard to topcoat — coal tar bleeds through
- Limited recoat windows between coats
Best for: Buried and submerged non-potable pipe exteriors, sewer and storm lines, piling, and field-coated fittings and joints.
Fusion-Bonded Epoxy (FBE)
FBE is a powder epoxy sprayed onto pipe that’s been blasted and heated in a coating plant. The powder melts, flows, and cures into a hard, thin film. It’s the default coating on a lot of modern oil, gas, and water transmission pipe.
Strengths:
- Excellent adhesion and very consistent quality from a controlled plant process
- Strong resistance to cathodic disbondment. The U.S. Army Corps of Engineers has reported FBE as superior for impact and cathodic disbondment resistance
- Available in NSF 61 formulations for potable water (AWWA C213)
- No coal tar
Weaknesses:
- Shop-applied only. Field joints, fittings, and repairs need a different compatible system (usually liquid epoxy)
- Brittle compared to thicker coatings. It chips and cracks from rough handling, bending, and rocky backfill
- Thin film means less margin for damage
- Higher moisture permeation than coal tar coatings, per published comparisons
Best for: New transmission pipe bought already coated from a mill or coating plant, especially where potable water service or strong cathodic protection performance is needed.
Asphalt and Bituminous Mastics
Asphalt coatings are petroleum-based rather than coal-tar-based. They’re often called “bitumastic” on job sites even though that’s technically Carboline’s coal tar brand. Don’t assume — read the data sheet.
Strengths:
- Low cost and easy to apply
- Good water resistance for damp proofing
- Some asphalt pipe coatings are NSF 61 and NSF 372 certified for potable water, which coal tar can’t be
- Self-priming, single-component options
Weaknesses:
- Softer than epoxies and easily gouged
- Less chemical and abrasion resistance than coal tar epoxy or FBE
- Can soften in heat
- Poor UV resistance
Best for: Damp proofing, lighter-duty buried steel, and applications where a certified NSF 61 asphalt product is specified.
How to Choose
Is it drinking water? Then the interior needs an NSF 61 certified product — liquid epoxy (AWWA C210), FBE (AWWA C213), cement mortar, or a certified asphalt. Coal tar epoxy is out. We explain why in Can You Use Bitumastic on Potable Water Pipe?
Is the pipe coming from a mill already coated? FBE is often the plant coating. Plan how field joints and fittings will be coated in a compatible system.
Is it being coated in the field or in a fab shop? Coal tar epoxy and liquid epoxies can go on anywhere. FBE can’t.
How rough is the handling and backfill? Rocky backfill and rough handling favor thicker, tougher systems, or FBE with an abrasion-resistant overcoat.
Does the owner allow coal tar? Check the owner’s standard before bidding.
Every One of Them Starts With the Blast
The coating chemistry is different, but every buried pipe coating failure we see traces back to the same handful of problems: mill scale left on the steel, oil blasted into the surface, a profile that’s too shallow or too rounded, dust left on the steel, or coating over flash rust.
FBE plants control this with automated blasting and inspection. Field-applied coal tar epoxy and asphalt depend on the blast crew doing it right. We cover coal tar epoxy prep specifically in Surface Prep for Coal Tar Epoxy, and the same principles apply to any immersion or buried coating.
Blasting Jack provides abrasive blasting and surface preparation for pipe, fittings, field joints, and buried steel across Michigan, prepped to whatever coating system your spec calls for. Contact us to talk through your next project.