How it differs from standard epoxy
Most general-purpose epoxy coatings use bisphenol A or bisphenol F resins, which have two epoxy groups per molecule. Epoxy novolac resins are made from phenol or cresol novolacs and carry several epoxy groups per molecule. When cured, they form a much denser three-dimensional network. That density is the source of their advantages — fewer paths for solvents and acids to penetrate, and a higher glass transition temperature — and of their main weakness: a stiffer, less forgiving film.
Formulations vary widely. Some products are pure novolac systems, others blend novolac with bisphenol resins, and the curing agent has as much influence on performance as the resin. The name alone does not define a performance level.
Where it is used
- Tank linings for crude oil, refined fuels, solvents and many chemicals, particularly where service temperature or chemical aggressiveness exceeds what a standard epoxy tolerates.
- Secondary containment, sumps and trenches exposed to spills of acids and solvents.
- Wastewater structures and basins, where biogenic acids attack concrete and conventional coatings.
- Process vessels and piping internals in chemical service.
Limits
- Relative brittleness: lower elongation and impact resistance than standard epoxies. Substrate movement, cracking concrete, thermal cycling and mechanical impact can crack the film.
- Application demands: working times and recoat windows can be tighter, and full cure is often required — sometimes with heat or forced curing — before chemical service.
- Cure-related defects: like other amine-cured epoxies, some systems are prone to amine blush when applied in cold, humid conditions.
- Not universal: resistance varies by chemical, concentration and temperature. Strong oxidizing acids and some solvents can still attack a novolac lining.
How to specify it
Selection starts with the manufacturer's chemical resistance chart and product data sheet for the exact chemical, concentration and maximum temperature, and, for critical service, with immersion testing of the candidate lining. The specification should define surface preparation, film thickness range, cure schedule before service and holiday testing of the completed lining, all according to the data sheet. For the wider choice of lining families, see concrete containment coatings.