How do I store and dispose of leftover paint?

Storing it so it is still usable next year, hardening water-based paint for disposal, and where solvent-based has to go.

Difficulty: beginner
Time: 30 min
Read: 4 min
Safety: warning

Short answer

Store tins upright, sealed, somewhere frost-free and not too warm. Water-based paint can be hardened with sawdust or cat litter and then binned once solid; solvent-based paint is hazardous waste for a household waste site. Never pour any of it down a drain.

Almost every household has old paint that is either unusable or awkward to get rid of, and both problems come from the same few decisions made when the job finished.

Safety

Never pour any paint down a sink, a drain or onto the ground — it is an offence and it reaches watercourses. Solvent-based paint, thinners and strippers are hazardous waste with separate arrangements and must not go in a household bin even when dry. Store paint away from frost and away from anything with a pilot light or that sparks.

Step by step

Decant into a smaller container.It is the air in a half-empty tin that skins and spoils paint. A small jar filled to the top keeps for years where the original tin will not.
Seal the lid properly.Clean the rim, put cling film or a plastic sheet over the opening, then press the lid down evenly with a block of wood rather than hammering the rim, which distorts it and stops it sealing.
Store upright and label it.Upright, not inverted — the inverted-tin advice risks leaks and does not help modern lids. Write the room, the colour name and the date on the lid, since colour codes fade and memory is worse.
Keep it frost-free.Water-based paint is ruined by freezing — it separates into a grainy mess that will not remix. An unheated garage or shed in a British winter is the usual place paint dies.
Do not store it too warm either.Near a boiler or in a loft that bakes in summer, it thickens and skins faster. Somewhere cool, dry and stable indoors is best.
Test old paint before using it.Remove any skin whole rather than stirring it in, then stir thoroughly and brush some on card. Water-based typically keeps two to five years sealed; solvent-based often longer. A rancid smell or lumps that will not disperse means it has gone.
Use it up first.Undercoat on a shed, priming, a utility room, a garage floor. Most leftover paint is disposed of when it could have been used somewhere that does not matter.
Offer it before disposing of it.Community RePaint schemes, local groups, schools, scout huts and men's sheds all take usable paint. It is free, quick and better than any disposal route.
Harden water-based paint to bin it.Stir in sawdust, cat litter or a proprietary paint hardener until it is solid all through, then leave the lid off until fully dry. Once genuinely solid it can go in general waste with the lid off — check your council, since rules vary.
Take solvent-based paint to a household waste site.It is hazardous waste regardless of whether it is dry. So are thinners, white spirit, paint stripper and brush cleaner. Most sites have a dedicated point and it is free.
Recycle the empty tins.Metal tins that are properly empty and dry go in metal recycling. Plastic tubs vary by council. A tin with wet paint in it is not empty.
Never wash brushes down a drain with solvent.Clean water-based brushes in a bucket and let the solids settle before disposing of the water. Solvent from cleaning oil-based brushes is hazardous waste — let the solids settle, reuse the clear solvent, and take the residue to the tip.
Buy the right quantity next time.Most leftover paint is over-ordering. Work out the area and the coverage rate rather than adding a spare tin by default.

Tips

Decant into a small jar filled to the top. Air is what ruins stored paint, not time.
Never let water-based paint freeze. One winter in an unheated shed and it is finished, whatever the tin looks like.
Community RePaint schemes take usable leftover paint and pass it on. Far better than hardening a good tin for the bin.

Common mistakes

Pouring paint down a drain or onto the ground — It reaches watercourses and it is an offence. Water-based paint must be hardened first and solvent-based goes to a household waste site.
Storing paint in an unheated shed over winter — Freezing separates water-based paint permanently into a grainy mess that cannot be remixed. Keep it somewhere frost-free.

If it doesn't work

Skin on the surface of the paint

Cause: Air in the tin — Fix: Lift the skin off whole rather than stirring it in, then strain the paint through old tights. Decant into a smaller container afterwards.

Paint grainy and will not remix

Cause: It has been frozen — Fix: It cannot be recovered. Harden and dispose of it, and store the replacement somewhere frost-free.

Lid will not seal after opening

Cause: Rim distorted by hammering the lid down — Fix: Clean the rim, cover with cling film and press the lid with a block of wood spreading the load.

Paint smells sour or rancid

Cause: Bacterial spoilage in water-based paint — Fix: It is finished — do not use it. Harden and dispose of it.

Tip will not take the paint

Cause: Liquid water-based paint in general waste — Fix: Harden it with sawdust or cat litter until solid all through, lid off, then present it dry.

Questions people ask

How do I dispose of leftover paint?

Harden water-based paint with sawdust or cat litter until solid, then bin it with the lid off. Solvent-based paint, thinners and strippers are hazardous waste for a household waste site. Never pour any of it down a drain.

How long does paint last once opened?

Water-based typically two to five years if properly sealed and kept frost-free; solvent-based often longer. Decanting into a smaller full container extends it considerably, because air is what spoils it.