TL;DR
Oil-based paint needs a solvent, and the method that works is two separate baths of mineral spirits followed by a soap-and-water finish. The used rags matter as much as the brush, because oil-finish rags can heat up and catch fire on their own if they are piled up.
Ventilate first, then set up
Open a window and a door, or work outside. Solvent vapors build up fast in a closed garage and they are heavier than air, so they collect low.
Keep every ignition source away. That includes water heater and furnace pilot lights, which sit at floor level in many garages and are exactly where solvent vapor pools.
Wear nitrile gloves. Mineral spirits strips oils from skin and repeated contact causes real irritation.
Set out three containers: two for solvent baths and one for the soap-and-water finish. Metal or glass is better than thin plastic for solvent.
Scrape the brush out before any solvent
Drag both sides of the brush against the can rim to return the paint. Then work the rest out onto newspaper or cardboard.
The less paint on the brush, the less solvent you need and the less waste you create afterward.
Wipe the brush with a rag or paper towel, pressing from the ferrule out to the tips. Set those rags aside for proper disposal, which the last section covers.
Do not rinse an oil-based brush in water first. Water does nothing to oil-based paint and just makes the brush harder to clean.
Why two solvent baths?
Two baths work because the first one does the heavy lifting and gets dirty fast, while the second one is nearly clean solvent that carries the last of the paint out. A single bath quickly becomes paint-in-solvent, and a brush pulled out of it dries with residue still in the bristles.
Pour just enough mineral spirits into the first container to cover the bristles. Work the brush against the bottom and sides, then comb it out.
Squeeze the solvent out of the brush against the container wall. Move to the second, cleaner bath and repeat until the solvent stays mostly clear.
Comb the bristles in the second bath too, from the ferrule outward. That base of the bristles is where paint cures and ruins a brush.
Mineral spirits, paint thinner, and odorless mineral spirits all work for oil-based paint and varnish. Lacquer and shellac need their own solvents, which the product label will name.
The soap and water finish
After the solvent baths, wash the brush in warm water with dish soap. This lifts the solvent residue that would otherwise stay in the bristles and stiffen them.
Work the suds through from the ferrule to the tips, then rinse until the water runs clear.
Spin or shake the water out, then shape the bristles back into their original chisel or point with your fingers.
Hang the brush bristles-down or lay it flat with the bristles past the edge of a surface. Never stand it on the bristles, and never leave it standing in liquid.
Once fully dry, wrap it in its keeper or in heavy paper so it holds its edge. This part of the routine is identical to how to clean latex paint brushes.
Natural bristle is the right brush here
Natural bristle brushes are the traditional and best choice for oil-based paint, stain, and varnish. They hold and release oil-based products beautifully.
The same brush in latex paint goes limp, because natural bristle absorbs water and swells. That contrast is the core of latex vs oil based paint brush cleanup.
Some synthetic blends handle oil-based products acceptably. Check the label on the brush.
A well-kept natural bristle brush lasts for years and gets better with use as the tips soften. It is worth the ten minutes of cleanup.
The rags are the dangerous part
Rags soaked in oil-based stain, varnish, or a drying oil can heat up on their own as the oil oxidizes. Wadded into a pile, that heat has nowhere to go and the pile can ignite with no spark at all.
Do not ball them up in a trash bin, a plastic bag, or a cardboard box. That is the exact setup that causes these fires.
Spread each rag out flat and single-layer on concrete or a metal surface outdoors, weighted so wind does not pile them, until they are stiff and dry. Or seal them in a listed metal oily waste can with a self-closing lid.
The full explanation, including which products carry the risk, is in why oily rags can catch fire on their own. It is worth reading once before your next varnish job.
Reusing and disposing of the solvent
Do not pour used mineral spirits down a drain, into a storm gutter, or onto the ground. It is household hazardous waste.
Pour the used solvent into a sealed glass or metal jar and let it sit. Over a few days the pigment and solids settle to the bottom and clear solvent rises to the top.
Pour off the clear solvent into a labeled container and reuse it. The sludge at the bottom goes to a household hazardous waste drop-off.
Check your county solid waste department for the current drop-off site and hours before you drive, since programs and locations change.
Store solvents in labeled original containers, tightly closed, away from heat and any ignition source. Never combine leftover products in one container, and never mix a solvent with any other cleaning chemical. For the rest of the shop and hobby gear, see our guide to cleaning tools, yard gear, and hobby equipment.
FAQ
Can you clean oil based paint brushes with soap and water?
Not on their own. Soap and water will not dissolve oil-based paint, so the brush needs a solvent such as mineral spirits or paint thinner first. Soap and water come afterward, to wash the solvent residue out of the bristles so the brush dries soft rather than stiff.
How much mineral spirits do I need to clean a brush?
Enough to cover the bristles in a narrow container, usually a cup or two split between two baths. A tall narrow jar uses far less than a wide tray. Reusing settled solvent from previous cleanups reduces both cost and waste considerably, since the clear layer pours off and works fine again.
Can I reuse mineral spirits after cleaning brushes?
Yes. Pour the used solvent into a sealed glass or metal jar and leave it undisturbed for a few days. Pigment and solids settle to the bottom and the clear solvent on top can be poured off and reused. The remaining sludge goes to a household hazardous waste drop-off.
Is it safe to clean brushes indoors with mineral spirits?
Only with real ventilation, and outdoors is better. Solvent vapors accumulate quickly in a closed room and are heavier than air, so they pool low where pilot lights sit. Open a window and a door, keep ignition sources away, wear nitrile gloves, and do not work in an enclosed space with no airflow.
How do I dispose of rags used with oil based paint?
Spread each rag flat and single-layer outdoors on concrete or metal, weighted down, until it is stiff and dry, or seal them in a listed metal oily waste can with a self-closing lid. Never pile them in a bag, box, or bin, since drying oils generate heat as they cure and a pile can ignite.
What is the difference between mineral spirits and paint thinner?
Both are petroleum solvents that dissolve oil-based paint and varnish, and for brush cleaning they are largely interchangeable. Mineral spirits is generally more refined, with less odor and fewer impurities, while paint thinner is typically a cheaper blend with a stronger smell. Odorless mineral spirits is the mildest option for indoor work.
Painting is one project and the rest of the house is another. If the second one needs a reset, our house cleaning services can help. Every home is different, so the real number depends on size, condition, and what you want covered. Get a quote and we will walk you through it.