Isocyanates And Two Pack Paint Waste Explained

A two pack product is supplied as a base (sometimes called the resin or colour component) and a hardener (sometimes called the activator or curing agent). The two are combined, usually in a stated ratio, immediately before application. Once mixed, the material has a limited working life (a pot life), after which it thickens and then sets, whether or not it has been used.

This is different from a one pack paint, which dries as its carrier evaporates and can in principle be left in a part-used tin indefinitely. A two pack product that has been mixed is on a one-way path to curing regardless of what happens to it next.

Isocyanates are reactive chemicals used in many two pack hardeners, particularly in vehicle refinish products, clearcoats and some industrial coatings. The Health and Safety Executive's guidance on 2-pack isocyanate paints explains that isocyanates are used in some water based paints, most base coats and almost all lacquers used in vehicle refinishing.

Not every two pack product contains isocyanates, because some use other hardener chemistries, so the presence of a second component does not automatically mean isocyanates are involved. The only reliable way to know is the product's own documentation.

Two pack waste is rarely one simple thing. Unused components, mixed-but-uncured material, gelled or partly cured residue, and fully cured material behave differently and need different information for an assessment. Treating them as interchangeable slows things down and risks an unsafe mix-up.

• Unused base or unused hardener: still in their original, separate containers and never combined.
• Mixed and still liquid: components combined but within, or shortly past, their pot life.
• Gelled or partly cured: mixed material that has thickened or set but is not yet a solid, inert mass.
• Fully cured: mixed material that has completed its chemical reaction and is now a solid.

Because the two components of a two pack system can have very different hazard profiles, we ask for details on each one separately rather than for the product as a single entry.

• Product name and, where possible, supplier and part number for both the base and the hardener.
• Whether the components have been mixed, and if so, approximately how long ago.
• Container condition: sealed, opened, damaged or leaking.
• Quantity of each component, and whether that is an estimate or a measured amount.
• Any safety data sheet you hold for either component.

The same caution applies to unlabelled containers found in stores. Rather than opening, mixing or sampling them, record what can be seen from the outside (size, condition, any residual labelling) and raise it as part of the enquiry.

Classification of isocyanate-containing and other two pack waste follows the government's waste classification framework, which looks at composition, origin and condition rather than a product's marketing description. The clearer your component-level information, the fewer follow-up questions an assessment needs.

If your site generates general solvent based coating waste alongside two pack materials, the route for that is covered on oil and solvent based paint disposal. Rags, masking and other materials contaminated by any of these products are covered on paint-contaminated materials disposal.