To install a marble threshold, dry-fit it in the doorway, make the floor under it flat, clean and solid, and undercut the door casing if the stone runs under it. Set it in thinset mortar on a tile job, or in a stone-rated adhesive on an existing floor, and check it for level and height against both floors. Finish the joints with grout or flexible sealant depending on the neighboring floor, let everything cure, then seal it.
What tools and materials do you need?
Most of this is already in a tile setter’s bucket. Gather it all before you mix anything, because mortar and adhesive only give you limited working time.
- The threshold, sized to the opening (read our measuring guide before you order)
- Tape measure, pencil, small square, a level and a straightedge
- Oscillating multi-tool or jamb saw for undercutting trim
- Thinset mortar suited to natural stone, or a stone-rated adhesive, with a notched trowel and bucket
- Rubber mallet and plastic shims
- Grout and float for the tile side; color-matched flexible caulk or sealant for movement joints
- Penetrating stone sealer and clean cloths
- Safety glasses, gloves, a dust mask, and a wet saw with a diamond blade only if you must trim the stone
How do you measure, dry-fit and prepare the floor?
Preparation decides whether a threshold lasts. Stone does not bend, so if it sits over a hump or a hollow, foot traffic flexes it and it can crack.
Measure and dry-fit
Measure the opening at floor level, jamb to jamb, in two or three spots, because openings are rarely square. Then set the stone in dry. Check the length, see where the closed door lands, compare the height on each side, and mark which long edge faces which room.
Prepare the substrate
- Remove the old threshold, nails, old adhesive and debris.
- Scrape down high spots and fill low spots with a patch product suited to the substrate.
- On a wood subfloor, check for bounce. Fixing a springy floor first is cheaper than replacing a cracked saddle.
- Vacuum, then wipe with a damp sponge so the mortar bonds to the floor, not to dust.
Do you need to undercut the door jamb or casing?
Yes, if the threshold runs the full width of the opening and slides under the casing or jamb. Notching stone around trim is fussy and rarely looks clean, so undercutting the wood is the normal approach.
Set the threshold on a spacer as thick as your mortar or adhesive bed. Rest the blade of the oscillating tool or jamb saw flat on top of the stone and cut the casing and jamb at that height. The stone should then slide in snug without forcing. Our standard stock is 3/4 inch thick; a 1-1/4 inch custom piece needs a deeper cut. Our threshold thickness guide helps you choose.
How do you set the threshold and get the height right?
On a tile job, the usual choice is thinset mortar suited to natural stone. Many installers use white thinset under light stone such as White Carrara, because gray mortar can show through. On an existing, sound floor with no new tile, a stone-rated adhesive is common. Either way, follow the mortar or adhesive manufacturer’s instructions for mixing, trowel size and working time.
Aim for full contact. Comb mortar onto the floor, back-butter the stone, and press it down with a slight side-to-side motion. Watch the ends: a void there is a common reason a saddle rocks or cracks later.
Check level and height
Lay the level along the stone, then across it. Tap it down with the mallet and recheck. The top should sit flush with the higher floor, or slightly above both, with no square lip anyone can catch a toe on. Turn the profiled edge toward the lower floor:
- Single Hollywood bevel: a long gentle slope on one long edge. The slope faces the lower floor.
- Standard bevel: a small 1/4 inch chamfer on one long edge only, with the other long edge square. Put the chamfer on the side with the step and butt the square edge against the floor it sits level with.
- Double Hollywood bevel: a long slope on each long edge, for a threshold that sits above both floors.
In commercial buildings, the 2010 ADA Standards limit doorway thresholds to 1/2 inch high. See our ADA threshold guide and check local code.
Grout or caulk: how do you finish the joints?
Fill each joint according to what is on the other side of it. Rigid grout works where tile and stone sit on the same substrate and move together. Anywhere two materials move differently, including a planned movement joint, use a flexible sealant.
| Where the joint is | What to use | Why |
|---|---|---|
| Threshold to tile on the same floor | Grout matching the tile grout | Both are bonded to the same substrate |
| Threshold to wood, laminate or vinyl plank | An expansion gap filled with flexible caulk or sealant, or the flooring’s own transition trim | These floors expand and shrink with humidity; grout cracks |
| Threshold ends against the door jamb | Color-matched flexible caulk | Wood trim and stone move differently |
Wipe grout haze off the marble promptly with a damp sponge. Do not use acid-based haze removers on marble or travertine, because acids etch the surface.
How long should it cure, and when do you seal it?
Let it cure as long as the mortar, adhesive, grout and sealant manufacturers specify. Cure time depends on the product, temperature and humidity, so read the labels. Keep foot traffic off the threshold until then.
After curing, apply a penetrating stone sealer to natural marble, granite or travertine per the sealer’s directions, and wipe off the excess before it dries on the surface. Engineered quartz is non-porous and does not need sealer. For ongoing care, see how to seal, clean and replace a marble threshold.
What are the most common installation mistakes?
- Voids under the stone. Partial coverage, especially at the ends, leads to cracks.
- Setting on a flexing floor. No amount of mortar fixes a bouncy subfloor.
- Bevel facing the wrong way. Dry-fit and mark the edges before you mix.
- Measuring at the top of the opening. Measure at the floor, where the stone sits.
- Grouting against wood. Rigid grout against a floor that moves will crack out.
- Acid cleaners on marble. Vinegar, many haze removers and some bathroom cleaners etch it.
- Leaving a lip. A square edge standing above the lower floor is a trip hazard.
When should you call a professional?
A single interior saddle over a sound floor is a fair DIY job if you have set tile before. Bring in an installer when:
- The subfloor is soft, damaged or noticeably bouncy.
- The floors differ by more than about 1/2 inch, which may call for floor work or a ramp rather than a threshold.
- It is a shower threshold, where waterproofing and slope toward the drain matter. See our custom shower threshold page.
- It is a commercial doorway that has to meet accessibility rules.
Ordering for several jobs? See our contractor page.
Measured your opening? Shop marble thresholds in stock lengths of 24, 30 and 36 inches, or request a custom size if your doorway is unusual.
Frequently asked questions
Can I install a marble threshold over an existing floor?
Often, yes, if the existing floor is solid, flat and well bonded. Clean it, prepare the surface the way the adhesive maker asks, and use a stone-rated adhesive. Check the finished height first, because setting on top of an existing floor raises the stone and can leave a lip.
Do I grout or caulk between the threshold and a wood floor?
Caulk, or use a flooring transition. Leave the expansion gap the wood flooring maker calls for and fill it with a flexible, color-matched sealant. Grout is rigid and cracks when the wood moves.
Do I need to seal a marble threshold after installing it?
Yes for natural marble, granite and travertine. Apply a penetrating stone sealer once the setting materials have fully cured, following the sealer’s directions. Engineered quartz does not need sealing.
Can I cut a marble threshold myself?
You can, with a wet saw and a diamond blade, cutting slowly with the full length supported. A factory edge looks cleaner at a visible joint, so if your opening is not a stock length, a custom cut from our Jersey City shop is often the simpler route.