TL;DR
Joint compound re-wets in water, so hitting a fresh blob with a damp rag turns a lump you could have removed into a paste soaked through the pile. Let it dry completely, break it up and lift the solids, vacuum thoroughly, then treat the remaining haze with a mild acid rinse. Drywall dust is a separate, easier problem that is dry vacuuming only.
Why the Instinct to Wipe It Up Is Wrong
Joint compound is gypsum powder mixed with water and a binder. It stays workable while wet, which is the point on a wall and the disaster on a carpet.
Wiping a fresh blob with a damp cloth does not remove it. It thins it, and the thinned compound flows down between the fibers, into the yarn twist, and onto the backing. When it dries there it forms a hard shell around individual fibers that a vacuum cannot break and detergent cannot dissolve fast enough to matter.
The correct approach is counterintuitive and it is the same one used for how to get dried mud out of carpet: walk away and let it dry hard.
What Should You Do With a Fresh Blob?
Scoop, do not wipe. Use the edge of a plastic card or a spoon to lift the bulk of the wet compound off the surface, working from the outside toward the middle so you do not push it wider.
Then stop. Do not add water, do not blot with a damp cloth, and keep foot traffic off the area. Let what remains dry completely, which usually takes a day for a thin smear and longer for a thick one. A fan on the area speeds it up.
Resist the urge to check it by pressing on it. Pressure on a partly dried lump forces compound deeper into the pile.
Breaking Out the Dried Compound
Once it is fully dry, the compound is brittle. Work it with your fingers or the edge of a stiff plastic card to crack it into pieces and separate it from the fiber. A soft brush helps break up what is caught in the yarn.
Do not use a wire brush or a metal scraper. Both cut carpet fiber, and fiber damage is permanent in a way the stain is not.
Then vacuum with the hose and a crevice tool, working outside-in. Skip the powered head, which flings gypsum dust across the room and grinds the fine particles in. Make slow passes from several directions, empty the machine, and repeat. Vacuum carpet the right way covers technique.
Expect this to take several rounds. Each cycle of breaking and vacuuming releases more.
Clearing the White Haze That Remains
After the solids are out, a chalky haze often stays, especially on dark carpet. That is fine gypsum bonded to the fiber, and it responds to acid rather than to detergent.
Gypsum is calcium sulfate, mildly alkaline in solution, so a dilute acid dissolves it. Mix about one part white vinegar to four parts cool water, dampen a white towel, wring it nearly dry, press onto the haze for a minute, then lift and check for transfer. Repeat with clean sections.
Rinse afterward with plain cool water and blot dry. This is the same reasoning behind how to do an acid rinse on carpet. Source: IICRC S100 carpet cleaning standard
If a greasy or tacky feel remains, some compounds contain a polymer binder. A small amount of neutral pH detergent on a damp towel handles that, followed by a thorough clean water rinse so you do not leave residue that attracts soil. Take the time to rinse the detergent out.
On wool, keep any vinegar solution dilute and skip oxygen bleach entirely, since wool cannot take oxygen bleach, high heat, or high alkalinity. See how to clean wool carpet.
Drywall Dust Is a Different Job
Sanding dust that settled into carpet is not the same problem as a compound blob, and it is much easier. It is dry particulate and the entire treatment is vacuuming.
Vacuum with the hose, empty the machine often, and expect to go over the area several times across several days. Fine gypsum dust settles gradually and works its way up through the pile as people walk on it, so a room that looked clean can look hazy again the next morning.
Do not shampoo or extract a dusty carpet before vacuuming it thoroughly. Wetting the dust makes exactly the paste you have been avoiding. Post-construction carpet cleaning always begins with heavy dry vacuuming for this reason.
One caution: sanding dust in a home built before the late 1970s may involve older materials, and the safe assumption in an old house is to have suspect materials tested rather than sanding and vacuuming blind. That is an environmental testing question, not a cleaning one.
When It Will Not Come Out
Compound that was wiped in while wet and then dried can encase individual fibers permanently. Professional cleaning removes a lot of it, but a slightly stiff, lighter patch sometimes remains.
The other lasting problem is abrasion. Gypsum particles are hard, and if the area was walked on before it was vacuumed, the fiber surface is scratched. That reads as a dull patch that no cleaning brightens, because it is texture damage rather than soil.
FAQ
Should I wipe up wet drywall mud on carpet?
No. Wiping thins the compound and drives it down into the pile and the backing, where it dries into a hard shell around the fibers. Scoop off the bulk with a card edge, then let the rest dry completely before touching it again.
How long should I let joint compound dry on carpet?
Long enough that it is hard and brittle, usually at least a day for a thin smear and two or more for a thick blob. A fan on the area speeds it up. Working it while it is still slightly soft pushes material deeper into the fiber.
Why is my carpet still white after vacuuming out the drywall?
Fine gypsum is bonded to the fiber, particularly if the area was ever damp. A dilute white vinegar solution in cool water dissolves it, because gypsum responds to acid rather than to detergent. Rinse with plain water afterward.
Can I use a carpet cleaning machine on drywall dust?
Only after thorough dry vacuuming. Running water over unvacuumed gypsum dust makes a paste that bonds to the yarn and is far harder to remove. As a final rinse after the dust is out, extraction works well.
Will drywall mud permanently stain carpet?
It can, if it was wiped in wet and allowed to dry inside the yarn. Most of it still comes out with drying, breaking, vacuuming, and an acid rinse, but a stiff or lighter patch sometimes remains, and abrasion from walking on it is permanent.
Do I need a special vacuum for drywall dust?
A vacuum with a good filter matters more than a special machine, because fine gypsum passes straight through a poor filter and back into the room. Expect to empty it frequently, since the dust clogs filters quickly and kills suction.
See also: carpet cleaning services. Enter your ZIP in the price box to see which services are available at your address.
Drywall mud is a case where the right first move looks like doing nothing, and the wrong first move is the one almost everyone makes with a damp rag. Let it dry, break it out, vacuum hard, then use acid rather than soap on the haze. If compound was wiped in wet or the area has been walked on since, that is worth having someone assess. Get a quote and we will tell you what is recoverable.
