Paint preservatives protect water-based paint from bacteria and fungi in the can. Without one the paint can smell, lose thickness and gas. Here you will find why water-based paint needs a preservative and how to choose and dose it.
An in can preservative for paint is added in small amounts, and a biocide for emulsion paint is usually part of the base formula.
We help you choose grades and suppliers, set simple receiving checks and keep your formula stable from lot to lot. IPCS (Indian Paints Consulting Service) offers raw material selection and sourcing guidance, including advice on paint preservatives.
Paint Preservatives overview
Water-based paint contains water and organic ingredients that microbes can feed on. Spoilage shows as a foul smell, loss of viscosity, gassing, separation, colour change or a drop in pH. A preservative prevents this for the shelf life of the paint.
Common in-can preservatives are in the isothiazolinone family, such as BIT, MIT and CMIT/MIT blends. They are used at low levels, typically under 0.1 percent of the paint by weight. Rules on use differ by country, so check your supplier's current data sheet.
Types of paint preservatives used in paint formulations
| Type | What it does | Where it fits |
|---|---|---|
| Isothiazolinone preservatives | Wide spectrum in-can protection | Emulsion paint, primers and putty paste |
| Formaldehyde-free blends | In-can protection with different safety profile | Paints with ecolabel needs |
| Dry-film biocide | Protects the dry paint from mould and algae | Exterior and humid-area paint (paint anti fungal additive) |
Applications of Paint Preservatives
Why does water based paint need preservative? Because it contains water and nutrients that microbes can use.
Choosing paint preservatives for a paint formulation
What to compare
- Spectrum against bacteria and fungi
- Compatibility with the binder and pH
- Preservative dosage in emulsion paint: follow the data sheet
- Rules in your country and export markets
- Cost in use
Quality checks on receipt
- Appearance and active content
- Compare with the supplier's data sheet
- Safe handling instructions
Storage and handling
Store in closed containers, away from heat and direct sun. Handle as the safety data sheet advises.
Frequently Asked Questions
Why does water based paint need preservative?
Water-based paint contains nutrients for bacteria and fungi, so without a preservative it can spoil in the can.
What is the preservative dosage in emulsion paint?
Typical in-can biocides are used at under 0.1 percent by weight, but follow your supplier's data sheet and test in your formula.
How to prevent bacterial growth in paint?
Use a suitable in-can preservative, keep tanks and tools clean, use clean water and close containers.
What are signs of paint spoilage?
Foul smell, loss of viscosity, gassing, separation, colour change and a drop in pH.
Do I need a paint anti fungal additive?
In humid or exterior use a dry-film biocide protects the painted surface from mould and algae.
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