Oily shop rags are the one piece of laundry in a house that can start a fire without any flame going near them, and that is not a figure of speech. Rags soaked in certain oils generate their own heat as the oil cures, and a crumpled pile holds that heat in. Everything else about washing them comes second to that.
The fire consideration with oily shop rags, said plainly
Some oils cure by reacting with oxygen in the air, and that reaction gives off heat. Linseed oil, tung oil, most oil based wood finishes, danish oil, teak oil and many stains all behave this way.
Spread thin on a table top the heat has somewhere to go and nothing happens. Crumpled in a pile in a bin, the surrounding fabric insulates it and the temperature inside the pile climbs.
If it climbs far enough, the rag ignites on its own. This is well documented, it happens to professionals as well as to people doing one project, and it happens hours after the work has finished.
Petroleum oils, motor oil, gear oil and cutting fluid do not cure the same way and are far less prone to this, but they are still flammable and no oily rag belongs in a heated dryer.
So the rules, and they are short. Never ball them up. Never drop them loose into a bin with other waste. Never put them in a dryer. Never leave them in a closed vehicle in summer.
Spread them out flat and singly on a non combustible surface outdoors until they have gone dry and stiff, at which point the reaction is finished, or keep them in a metal container with a tight lid, or submerge them in water in a sealed metal can until you can deal with them properly.
What happens before they get anywhere near a machine
Shop rags arrive at the laundry already carrying more than a machine can reasonably deal with, so a few minutes of preparation decides how the wash goes.
Scrape and wipe first. The bulk of grease should come off mechanically, because a washer removes what a wipe cannot rather than doing the whole job.
Shake grit, swarf and metal filings out over a bin outdoors. Metal shavings scratch a drum, sit in the seal, and turn up in whatever goes in next.
Sort by what is on them. Finish and solvent cloths in one pile, motor oil and grease in another, ordinary dirty work cloths in a third, and treat the first pile as the one with the heat consideration attached.
Cloths carrying solvent should be aired outdoors until the solvent has evaporated before they go into water. A washing machine is not the place to be handling it.
Anything with dried paint on it is finished. Cured paint does not come out and it will keep flaking into the drum.
A cloth soaked in something you cannot identify is not worth the trouble. Dispose of it rather than washing it.
Why cold water guarantees failure
What is on shop rags is grease and oil, and neither is soluble in water at any temperature. They come out by being emulsified, which means broken into droplets and held in suspension long enough to drain away.
Emulsification needs three things working together, which are surfactant, agitation and heat, and heat is the one people leave out.
Below roughly body temperature most greases are effectively solid, so the detergent has a hard surface to work on and very little happens.
Hot water softens the oil and lets the surfactant get around it and lift it. This is one of the few loads where the hottest setting available is the right answer.
Use a degreasing detergent, or add a good squeeze of dish soap, which is built for exactly this job and costs almost nothing.
An hour long pre soak in hot water with a degreaser does more good than any cycle setting on the machine. Overnight is better for anything badly loaded.
Washing shop rags on their own, always
Never with clothing. Never with towels. Never with bedding. Never with anything you would be annoyed to lose.
Oil lifted in the wash is suspended in the water, and suspended oil settles onto whatever else is in the drum before the cycle ends.
Redeposited oil is invisible on a rag and obvious on a shirt, where it shows up as a grey haze across the fabric or as dark spots that only appear once the garment has been dried.
Keep the loads small. A drum half full of rags gets washed properly, and a packed drum of them just moves oil from one cloth to another.
Two cycles is normal rather than a sign of failure. The first carries the bulk away, the second gets what is left, and the water in the second one tells you how far along you are.
Run the machine empty afterwards on the hottest cycle it has, with detergent or a cup of washing soda in it, to clear residue out of the drum, the seal and the drain line before ordinary laundry goes back in.
Why softener and bleach have no place in this load
Fabric softener coats fibre with a water repelling layer, and a rag exists to absorb. Softening one removes the only thing it is for.
A softened cloth smears rather than wipes, which is obvious the first time you try to clear a bench with it.
Bleach does nothing at all to oil. It attacks colour, and a work cloth has no interest in colour, and it weakens cotton at the same time.
Skip fragrance for the same reason. Nothing in a workshop is improved by scented cloths and the perfume is one more thing sitting in the fibre.
What actually helps is washing soda, which raises the pH of the water and helps break down some greases into something the water can carry.
White vinegar in the rinse is worth using on cloths that have gone stiff, since stiffness is usually detergent and mineral buildup rather than oil.
Drying, and why a machine is the wrong choice
There are two reasons and either one on its own settles it.
Heat plus whatever oil is still in the cloth is the exact combination behind the rule at the top of this article, and no wash strips a heavily loaded rag completely.
The other reason is transfer. Residual oil comes off in a dryer drum, sits there, and moves onto the next several loads that go through it. A dryer with oil in the drum is a problem that lasts for weeks.
Air dry shop rags on a line or a rack instead, spread out with air reaching both faces rather than hung in a bunch.
Rags dry quickly because they are small and thin, so this is a matter of hours in warm weather rather than a real inconvenience.
If a machine really is unavoidable, restrict it to cloths that have been through two washes and carry no smell of oil at all, run it on low, and take them out the moment it stops.
When a rag is finished, and what a shop with volume should do
A rag is finished when it stops absorbing. Put it on a wet bench and watch whether it takes the water up or pushes it around.
It is also finished when it stays stiff after a wash, when it sheds fibre onto every surface it touches, when it has hard patches of cured finish in it, or when it still smells of oil after two hot cycles.
Cut old bath towels and worn cotton shirts into rags rather than buying them. Terry for soaking things up, knit cotton for wiping and polishing, and no synthetic fleece, which smears oil around and melts against anything hot.
Keep two containers, one for clean cloths and a metal one with a lid for used ones, and empty the used container on a schedule rather than letting it fill up over a month.
A shop going through shop rags in any real volume should look at a commercial laundry arrangement, which takes the washing off site and uses equipment built for oil bearing textiles and set up to handle the residue.
That is also the sensible answer for anyone who simply does not want oil residue anywhere near the machine their clothes go through.
The Dundalk part
This is a working area with a long industrial history and a waterfront that goes with it, so the number of households here with a garage full of tools, a trailer, a boat or a truck being kept running is high. Shop rags accumulate faster here than in a neighbourhood where nobody owns a socket set.
Humid summers are the local factor that matters most, and they cut two ways. A damp oily cloth left in a closed container in July does not dry out and finish reacting, it sits wet and sours, and moisture also helps a pile hold together as one mass instead of drying out as separate pieces.
So spreading them out with air moving over them matters more here than it would somewhere dry. A fan on a rack in a garage does more for a batch of work cloths than anything else, and a cloth that stays damp for three days develops a musty smell that survives a hot wash and comes straight back the next time it is wet.
Salt air is the third factor for anyone working near the water. Cloths used around boats, trailers and outboard gear carry salt as well as oil, and salt crystallises in the fibre as it dries and makes the cloth abrasive and stiff. A cold rinse first, before any hot wash, gets the salt and the grit out, and doing that in cold water rather than hot also keeps the grease from spreading through the whole load before you have started.
Where heavy work cloths can have a machine to themselves
The whole rule with work laundry is that it never shares a drum, which is easier to follow when the drum is not the only one you have.
The machines at our self-service laundry on Merritt Boulevard hold a hot load of coveralls and heavy work cloths with enough water in the cycle to actually carry emulsified grease out of the fabric instead of moving it from one item to another, and using a machine that is not the one your clothes go in keeps residue out of the next load.
Our machines and the store are cleaned daily.
Nou wash-dry-fold service covers the everyday laundry.
For general guidance, The American Cleaning Institute publishes a stain removal guide that is a useful cross-check.
The short version
Shop rags soaked in curing oils such as linseed, tung or most oil based finishes generate heat as they cure, so never ball them up, never bin them in a heap and never put them in a dryer. Spread them flat outdoors until stiff, or keep them in a sealed metal container. For washing shop rags, scrape the bulk off first, shake out grit, then pre soak in hot water with a degreaser or dish soap, because cold water will not release oil at all. Wash them entirely separately, in small loads, twice if needed, then run the machine empty and hot afterwards. No softener, no bleach, and air dry rather than tumble.
WaveMAX Dundalk is at 1774 Merritt Blvd, easy to reach from Dundalk and the surrounding area. If you have bedding that will not fit at home, call us at 443-216-7091.