What do I do with uncured silicone leftovers

Uncured silicone carries the hazard properties stated on the label. The simplest and cheapest solution is to turn the leftover from a chemical waste into an inert material by simply letting it cure.

Mix the leftover of component A with the matching amount of component B in the prescribed ratio, pour it out in a thin layer into a disposable cup or onto a sheet of foil, and let it cure fully in a ventilated space. A thin layer cures faster and more reliably than a thick lump, and condensation cured silicone needs ambient humidity for the reaction. Once the material feels completely dry and cured through, it is ordinary silicone rubber and can go in general or residual waste.

If curing is not possible, for example because the counterpart is missing or because the catalyst of an expired batch has lost its activity, the material remains a chemical waste. Private users hand it in at a household hazardous waste collection point or civic amenity site. Businesses dispose of it through a licensed waste contractor, with the appropriate European List of Waste code and the documentation required in their country.

Never pour anything down the drain. Silicone is neither soluble nor biodegradable, it passes through the treatment plant and ends up in the sludge or in surface water.

Section 13 of the safety data sheet of the product is always leading, it states the disposal route prescribed by the manufacturer. Collection arrangements themselves differ per country and per municipality.

Read more: working safely with chemicals