Chlorinated Rubber & Vinyl Coatings
Chlorinated rubber and vinyl lacquers once protected ships, pools, locks and dams. Today they are mostly a maintenance concern, shaped by VOC rules and raw-material restrictions.
Key takeaways
- Chlorinated rubber and vinyl coatings are thermoplastic lacquers that dry purely by solvent evaporation and remain soluble in their own solvents.
- They offered excellent water resistance and easy recoating and were long used on hydraulic structures, ships, pools and concrete.
- High solvent content, VOC limits and restrictions on raw materials have pushed most users to epoxies, urethanes and acrylics.
- Many existing structures still carry these coatings, so compatibility and safety in maintenance remain important.
Before high-solids epoxies and urethanes became dominant, many of the most demanding immersion and marine exposures were handled by solvent-borne lacquers based on chlorinated rubber or vinyl resins. They protected lock gates, dam spillway gates, penstocks, ship hulls and superstructures, swimming pools, traffic markings and masonry.
These coatings are rarely specified for new work today, but they are far from gone. Engineers and contractors maintaining older infrastructure meet them regularly and need to understand how they behave.
How these lacquers work
Both types are thermoplastic: the resin is already a high molecular weight polymer when it is dissolved in solvent. After application, the solvent evaporates and the polymer chains entangle into a film. No chemical cross-linking takes place, so the dried film can be redissolved by the same strong solvents that carried it.
This has two consequences. First, each new coat partly dissolves the previous one and fuses with it, giving excellent intercoat adhesion and making touch-up straightforward. Second, the film is sensitive to solvents, softens with heat and requires relatively low solids to keep viscosity workable, so many thin coats are needed. Rapid surface drying can also trap solvent below, a problem described in solvent entrapment.
Chlorinated rubber
Chlorinated rubber is made by chlorinating natural or synthetic rubber to a high chlorine content, producing a hard, brittle resin that is combined with plasticizers such as chlorinated paraffins. The resulting films have low water-vapor permeability and good resistance to water, dilute acids and alkalis. Production historically relied on chlorinated solvents that were later phased out under international ozone-protection agreements, and some chlorinated paraffin plasticizers have since been restricted, which helped drive the shift to alternatives such as chlorinated polyolefins and acrylic resins.
Vinyl coatings
Vinyl coatings are usually based on copolymers of vinyl chloride and vinyl acetate, sometimes modified to improve adhesion. They form tough, flexible films with very good resistance to fresh and salt water and to abrasion from debris, which made them a long-standing choice for hydraulic structures. Related products include polyvinyl butyral wash primers used as pretreatments on metals. Vinyl coatings should not be confused with vinyl ester linings, which are thermoset resins with entirely different chemistry.
Typical historical uses
| Exposure | Typical coating | Why it was chosen |
|---|---|---|
| Lock and dam gates, penstocks | Vinyl | Immersion and abrasion resistance; easy repair |
| Ship superstructures and hulls | Chlorinated rubber or vinyl | Water resistance; recoatable in any season |
| Swimming pools | Chlorinated rubber | Water and pool chemical resistance; easy recoat |
| Concrete and masonry | Chlorinated rubber | Alkali resistance; no saponification |
| Traffic and road markings | Chlorinated rubber | Fast dry; durable |
Modern alternatives for these uses are covered in marine coatings and swimming pool coatings.
Advantages and limitations
Advantages
- Excellent intercoat adhesion; coats fuse together
- Simple touch-up and repair without heavy abrasion
- Good water and chemical resistance for their thickness
- Dry quickly and can be applied at low temperatures
- Single-component, with no pot life
Limitations
- Low solids and high VOC; many coats required
- Poor resistance to strong solvents, oils and fats
- Soften at elevated temperatures
- Prone to solvent entrapment and blistering if built too fast
- Raw-material and VOC restrictions limit availability
Why they declined
The main driver was solvent content. Lacquers that dry only by evaporation typically contain far more solvent than modern high-solids coatings, and air-quality rules on VOC emissions made many formulations non-compliant in numerous regions; see VOC regulations. Raw-material restrictions added pressure, and owners increasingly favored high-build epoxy and polyurethane systems that reach target thickness in fewer coats.
Product availability now varies widely by country and region. Where a “chlorinated rubber” product is offered, it may be based on substitute resins with similar properties; check the safety data sheet and product data sheet for the actual composition.
Maintaining existing systems
Overcoating a vinyl or chlorinated rubber system needs particular care. Strong solvents in many modern coatings can soften, wrinkle or lift the old lacquer, while the cure shrinkage of thick thermoset coatings can pull a weakly bonded old film off the steel.
Many older vinyl and chlorinated rubber coatings on structures from the mid-twentieth century were pigmented with lead or chromate compounds. Test for hazardous metals before any surface preparation, and follow applicable lead and hazardous-waste regulations.
A practical approach is to identify the existing coating (solvent rub tests help: a thermoplastic lacquer softens quickly under strong solvent), assess its adhesion and thickness, and run trial patches of the proposed system. Options range from touch-up with compatible lacquer, where still available and permitted, to overcoating with a surface-tolerant system, to complete removal and replacement.
When removal is chosen, abrasive blasting is usual, but the soft, thermoplastic nature of these films can make them gum up on power tools and abrasive. Chemical strippers and waterjetting are sometimes used, with containment and waste handling planned around any hazardous metals present. Whatever the route, recording the existing system’s type, thickness and condition in the maintenance file helps the next crew avoid repeating the same investigation.
Frequently asked questions
Are chlorinated rubber coatings still made?
Availability varies by region. Many products sold under the name now use alternative resins with similar properties because of raw-material and VOC restrictions.
How can I tell if an old coating is vinyl or chlorinated rubber?
A solvent rub with a strong solvent will soften a thermoplastic lacquer quickly, whereas a cured epoxy or urethane resists. Laboratory analysis can confirm the resin type.
Can I put epoxy over an old vinyl coating?
Sometimes, but solvent attack and shrinkage stress can lift the vinyl. Test adhesion and use trial patches with the manufacturer’s recommended system.
Educational reference. Coating performance varies by formulation. Always follow the manufacturer’s product data sheet, safety data sheet and your project specification.
