How long before tile can go on dry pack?

Walking on it

Because dry pack is mixed with very little water, it firms up within hours and can usually take careful foot traffic the next day. It is still green at that point: it should not be loaded with heavy material, dragged across or chipped at the edges.

Membranes and tile

Many waterproofing membranes and many thinset mortars can go onto a mortar bed once it is firm and has set, often the next day. Some liquid membranes ask for a drier surface and a longer wait, and some sheet systems have their own rules for how fresh the bed may be. The waterproofer and the tile setter follow the sheets for the products they use.

Large-format tile and natural stone are less forgiving of a bed that is still moving, so setters often wait longer before setting them, especially on a thick bed.

Wood, vinyl and other moisture-sensitive floors

Engineered wood, vinyl plank, some glue-down floors and many floor adhesives are sensitive to moisture coming up from below. Over a screed, the flooring installer tests the moisture before laying them, and waits until the reading is within the maker's limit. A thick screed in a cool basement can take weeks to get there.

What speeds it up and what slows it down

Warmth and moving air help; cold, damp air slows the cure. A basement in winter dries far slower than a heated room upstairs in summer.

Forcing it does harm. Turning in-floor heating on hard to dry a fresh screed can crack it: heating is brought up gradually, on the schedule the heating maker gives. Outdoor beds are not laid when frost is expected, and a fresh bed is kept from freezing until it has set.

Full strength

Like concrete, a mortar bed keeps gaining strength for weeks; the figure usually quoted for full strength is about 28 days. Nobody waits that long to tile. The next trade starts when the products going on top allow it, and the finished floor is ready for normal use once those products have cured.

Thickness matters

A shower bed an inch or two thick dries much faster than a three-inch screed over heating tubes in a cool basement. The thicker the bed and the colder the room, the longer the wait for anything that needs a dry surface. A thick bed also shrinks a little more as it cures, which is one more reason the mix is kept lean and well packed.

How the next trade checks it

Before setting anything, the waterproofer or tile setter checks that the bed is hard, flat and sound. A scratch with a nail should not dig in or dust; a tap with a hammer should sound solid, not hollow; and a straight edge should show no humps or dips beyond what the tile allows. Dust and loose sand are vacuumed off, and any primer the membrane or thinset maker calls for goes on first.

If the bed fails any of those checks, it is fixed before the next layer goes on: a soft area is cut out and repacked, and a low spot is filled with the same mortar, not with extra thinset.