More rugs are damaged during drying than during washing. A rug that dries slowly at the foundation grows mildew, and a foundation that stays damp rots — neither of which is visible until it is done.
The deadline
Dry within 24 to 48 hours
Beyond that, mildew begins. On a cotton foundation it does not stop at smell — prolonged damp weakens the warp and weft, and dry rot cannot be economically repaired, only rewoven. Everything below is in service of hitting that window.
Get air to both faces
The single most important thing, and the one people get wrong by leaving a rug flat on the floor.
A rug lying face-up on a floor is drying from one side only, and the underside — where the foundation is — is sealed against a cool surface. That is the slowest possible arrangement and the one most likely to produce a musty rug.
Hang it over a rail, a bannister or a line, with the weight distributed rather than creased over a thin edge. Or raise it on blocks or upturned crates so air moves underneath.
Move the air
A domestic fan makes an enormous difference and is worth setting up properly rather than pointing vaguely at the room.
Aim it along the rug rather than at it, so air travels across both faces. Reposition it every few hours. A dehumidifier in the room helps more than heat does.
Squeegee first
If the rug is genuinely wet rather than damp, remove water mechanically before you rely on evaporation.
A rubber-bladed squeegee pulled firmly in the direction of the pile pushes water out of the base of the pile, which is where it hides. Repeat until no more comes. This alone can halve drying time.
Check the base, not the surface
A rug that feels dry on top can be wet against the foundation, and that is the part that matters.
Part the pile with your fingers down to the base and feel there. Do it in several places — the centre and any area that was heavily wetted dry last.
What not to do
Direct sun for long periods. It dries fast and fades unevenly and permanently, and wet fibre photodegrades more readily than dry. A short spell is a reasonable trade if mould is the alternative; an afternoon is not — rug colors.
Heat guns, hairdryers or radiators. Localised heat shrinks a cotton foundation unevenly and can felt wool.
Folding or rolling while damp. Traps moisture in the fold and creates exactly the conditions you are trying to avoid.
Putting it back on the floor "to finish". The floor is where it will not finish.
Drying it flat and to shape
If a rug has been thoroughly wetted it will want to distort as it dries. Professional plants dry rugs under mild tension for this reason.
Domestically: lay it flat once it is no more than damp, square the edges by hand, and weight the corners lightly. A rug dried in a ripple keeps the ripple.
If it has already dried out of shape, blocking — wetting and stretching it flat — is a professional job and a routine one, see rug repair.
After an accident rather than a wash
A leak, a burst pipe or a flood is the same problem at greater scale and with more urgency. Lift the rug off the floor immediately, get air moving, and check the pad and the floor beneath — both hold water longer than the rug does.
If it has been wet for more than a couple of days, get it professionally assessed before spending on cleaning: a rotted foundation is frequently not worth recovering — musty smell.
Common questions
How long does a wet rug take to dry?
With air on both faces and a fan, twelve to twenty-four hours for a low-pile rug and up to forty-eight for a thick one. Lying flat on a floor with no airflow beneath, it can take days — which is long enough for mildew to start.
Can you dry a rug in the sun?
Briefly and with care. Sun dries fast and UV kills mould spores, but it also fades unevenly and permanently, and wet fibre is more vulnerable to photodegradation than dry. Shade with moving air is the better default.