Ask five people on a job site what Bitumastic is and you'll get five answers. Some call it tar paint. Some think it's the same thing as roofing asphalt. Some use the word for any heavy black coating on a buried pipe. None of that is quite right, and the confusion leads to the wrong product going on the wrong surface.
Bitumastic is a brand name owned by Carboline for its family of coal tar coatings. The two products most people mean when they say “Bitumastic paint” are Bitumastic 50, a single-component coal tar mastic, and Bitumastic 300M, a two-component coal tar epoxy. They look the same in the can. They do very different jobs.
Bitumen vs. Coal Tar: Not the Same Material
The name sounds like “bitumen,” and a lot of people assume Bitumastic is an asphalt product. It isn't. Bitumen (asphalt) is the heavy residue left after refining crude oil. Coal tar is a byproduct of turning coal into coke for steelmaking. Both are black, both repel water, but coal tar has much lower water vapor permeability and better resistance to soil chemicals, bacteria, and root penetration. That's why it has been used for decades on buried and submerged steel.
The trade-off is health. Coal tar contains polycyclic aromatic hydrocarbons (PAHs), and coal tar pitch is classified as a known human carcinogen. That doesn't make coal tar coatings illegal for industrial use, but it does mean they have to be applied with proper respiratory protection, skin protection, and ventilation. We cover the regulations in detail in Is Coal Tar Being Phased Out?
Bitumastic 50: Single-Component Coal Tar Mastic
Bitumastic 50 is an ultra-high-build, one-part coal tar mastic. There's nothing to mix except stirring the can. It's self-priming and goes on thick, and it stays soft after it dries.
- Recommended thickness: 18 mils dry film thickness (DFT) in one or two coats. Carboline does not recommend less than 12 mils or more than 30 mils total.
- Volume solids: 68% ± 2%
- Cure behavior: Designed to stay soft and self-healing. Minor scuffs flow back together.
- Surface prep: SSPC-SP2 or SP3 hand/power tool cleaning at minimum for non-immersion; SSPC-SP6 commercial blast for maximum protection; SSPC-SP10 for immersion.
- Specs it meets: MIL-C-18480-B and Bureau of Reclamation CA-50.
- Backfill: Can start 7 days after the final coat, provided the surface has stayed above 60°F.
Where it belongs: foundation walls, below-grade damp-proofing, buried steel, piling, and the underside of structures that will never see sunlight. See our full breakdown in Protecting Below-Grade Steel and Concrete.
Bitumastic 300M: Two-Component Coal Tar Epoxy
Bitumastic 300M is a coal tar epoxy polyamide. It is a true two-part coating, mixed 4:1 (Part A to Part B), and it cures hard through a chemical reaction. That cured epoxy film is what gives it abrasion, chemical, and immersion resistance that a mastic can't match.
- Recommended thickness: 16 mils DFT in one or two coats; 16–24 mils achievable in a single coat, up to 35 mils total with force curing.
- Volume solids: 74% ± 2%
- Immersion limit: 120°F maximum. Dry heat to 350°F continuous.
- Specs referenced: Corps of Engineers C-200/C-200a, AWWA C210 (exterior), SSPC-Paint 16, STI-P3, MPI #35.
- Cathodic protection: Compatible with controlled cathodic protection systems.
- Performance data: 2,000 hours ASTM B117 salt fog with no blistering, rusting, or measurable undercut at scribe (Carboline lab data).
Where it belongs: tank linings, sumps, trenches, pipe exteriors, pilings in splash and immersion zones, wastewater structures, and marine steel. More on that in Coal Tar Epoxy for Wastewater Sumps, Trenches and Tank Linings.
“Bitumastic 50 stays soft on purpose. Bitumastic 300M cures hard on purpose. If you need abrasion or immersion resistance, the mastic is the wrong product no matter how thick you put it on.”
Bitumastic 50 vs. Bitumastic 300M at a Glance
| Bitumastic 50 | Bitumastic 300M | |
|---|---|---|
| Type | Coal tar mastic | Coal tar epoxy polyamide |
| Components | One | Two (4:1) |
| Typical DFT | 18 mils | 16 mils |
| Film | Stays soft, self-healing | Cures hard |
| Best use | Below grade, damp-proofing, buried steel | Immersion, linings, sumps, pipe, piling |
| Max immersion temp | 120°F | 120°F |
| Potable water | No | No |
Where Neither Product Belongs
Both data sheets carry the same hard limitation: do not use for potable water. Drinking water tanks and pipe need an NSF/ANSI 61-certified lining, and coal tar products don't qualify.
Coal tar also doesn't hold up well in direct sunlight. Exposed to UV, it chalks and fades from glossy black to a dull brown. It still protects the steel for a while, but it looks bad, and Carboline lists topcoats as not recommended for 300M. Coal tar tends to bleed through most paints put over it. If the surface is exposed and appearance matters, spec an epoxy and urethane system instead. We cover that in Specialty Coatings: Epoxy, Urethane and Zinc.
Coal tar is also a poor choice for anything hot and wet. Above 120°F immersion, you're into novolac epoxy territory. See Novolac Epoxy Tank Lining.
Not Sure Which Coating Your Steel Needs?
Tell us the substrate, the exposure, and whether it's buried, submerged, or in the open. We'll recommend a system and quote the prep and application.
Request a Free QuoteHow to Choose
- Buried or below-grade, no abrasion, needs to be cheap and thick: Bitumastic 50.
- Immersion, wet/dry cycling, abrasion, or chemical splash: Bitumastic 300M.
- Drinking water: Neither. Use an NSF/ANSI 61 epoxy.
- Exposed to sunlight where appearance matters: Neither. Use epoxy primer plus urethane topcoat.
- Project spec prohibits coal tar: Use a coal-tar-free high-build epoxy. Many owners and agencies now write this into specs.
Whatever the product, the coating is only as good as the surface under it and the thickness that ends up on the steel. Our Bitumastic application guide covers prep standards, mil thickness, and the 24-hour recoat window that trips up a lot of crews.
Frequently Asked Questions
Is Bitumastic the same as bitumen or asphalt paint?
No. Bitumastic is a Carboline brand of coal tar coatings. Coal tar comes from coal, while bitumen (asphalt) comes from crude oil. Coal tar has lower water vapor permeability and better resistance to soil chemicals and bacteria.
What is the difference between Bitumastic 50 and Bitumastic 300M?
Bitumastic 50 is a single-component coal tar mastic that stays soft and is used mainly below grade. Bitumastic 300M is a two-component coal tar epoxy that cures hard and is used for immersion, tank linings, sumps, pipe, and piling.
Can Bitumastic be used for potable water tanks?
No. Carboline's data sheets for both Bitumastic 50 and Bitumastic 300M state they should not be used for potable water. Drinking water service requires an NSF/ANSI 61-certified lining.
Can you paint over Bitumastic?
Carboline lists topcoats as not recommended for Bitumastic 300M. Coal tar tends to bleed through most paints applied over it. If appearance matters, use an epoxy and urethane system instead of coal tar.
How thick should Bitumastic be applied?
Bitumastic 50 is typically applied at 18 mils dry film thickness, within a 12 to 30 mil range. Bitumastic 300M is typically applied at 16 mils dry, up to 35 mils total.
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