How do I regrout a shower?

The short version

Regrouting a shower is a patient, messy, low-cost job that most careful homeowners can do. You remove the failing grout, pack in fresh cement grout, clean the tile before it hardens and keep the shower dry while it cures. The corners and the tub joint are different: they get caulk, not grout.

Start by working out why the grout failed. Crumbling, cracked or missing grout is common, but dark staining may be mold, and a leak behind the tile is a bigger problem than any grout. EPA's advice is to fix plumbing leaks and other water problems as soon as possible.^[3] Scrub mold off hard surfaces with detergent and water, and dry completely.^[3]

Grout for the flat joints, caulk for the corners

Grout is rigid. The joints where a wall meets a wall, or where the wall meets the tub or shower base, flex slightly as a house settles and as materials expand and contract. One grout manufacturer's data sheet says: "Not for use in movement joints or changes of plane" and adds that movement joints are required for perimeters and other changes of plane in all installations.^[1]

So the plan is grout in the flat joints between tiles and flexible silicone caulk at corners and changes of plane.^[2] Do not caulk over mold: EPA says not to paint or caulk moldy surfaces.^[3]

What you need

• A hand grout saw or an oscillating tool with a grout blade
• A vacuum, a bucket, a small-pore grout sponge and cheesecloth
• A rubber grout float
• Cement grout in a colour that matches, and 100% silicone caulk for the corners
• Nitrile gloves, safety glasses and an N95 respirator

The protective gear matters. The grout data sheet recommends impervious gloves, such as nitrile, safety glasses, and a NIOSH N95 respirator.^[1] Its health warning says the product causes severe skin burns and serious eye damage, and that prolonged or repeated inhalation of dust may cause lung damage or cancer.^[1] The product contains silica sand and portland cement,^[1] so sanding or sawing old grout makes dust you should not breathe. Vacuum often rather than sweeping.

Remove the old grout

Rake out the grout that is cracked, crumbling or loose. You do not have to remove every joint if the rest is sound, but a patchwork of colours never looks right, and a full wall is easier to match. Go slowly near tile edges. Skipping across a glazed edge leaves a chip you cannot undo.

Vacuum the joints and wipe them with a barely damp sponge. The new grout needs a clean, dust-free joint to bond to.

Mix and apply

Follow the bag. For the sanded grout this answer draws on, the mix ratio is 2 to 2.5 quarts of clean water to a 25-pound bag, or 1 to 1.25 pints to a 7-pound bag.^[1] Mix to a smooth, lump-free consistency (approximately 3 minutes), let the mixture stand for 5 minutes, then remix and use it.^[1] If it stiffens, do not add water, which can weaken the grout.^[1] That sanded product is meant to fill joints 1/8 inch to 1/2 inch wide;^[1] narrower shower joints often call for unsanded grout, so match the grout to your joint width.^[1]

Work one small area at a time. Holding a rubber grout float at a 45 degree angle, completely fill the joints, then hold the float at 90 degrees to remove the excess.^[1] Do not spread more grout than can be cleaned within 30 minutes of the grout firming.^[1] In a shower that means a few square feet at a time.

Then smooth the joints with a damp sponge in a circular motion, rinsing it often. Haze can be removed after 3 hours with cheesecloth or a wrung-out sponge.^[1]

Recaulk the corners

Remove the old caulk, then clean the joints: remove all dirt, dust, and old caulk from the joints.^[2] Apply masking tape to each side of the joint, fill the joint completely, and smooth the caulk within 5 to 7 minutes before pulling the tape.^[2] LATICRETE says 100% silicone caulk is best for caulking bathtubs and showers, offering the greatest durability.^[2] Apply caulk within the temperature range of 40 to 90 degrees F; silicone sets in under 20 minutes and fully cures in 24 hours.^[2]

Cure, then seal if you want

Do not open the grout to foot traffic before it has cured for 16 hours, and maintain temperatures above 50 degrees F for at least 72 hours for proper cure.^[1] For a shower, that means roughly three days without use.

Sealing is optional. To test an older sealer, drop a small amount of water on the grout. If the water droplets bead up, the sealant is fine. If the water is absorbed into the grout, it is time to reseal.^[4]

Stop and call a pro if

• The tile is loose or sounds hollow. Grout cannot hold tiles that have let go of the wall.
• The wall behind the grout feels soft or smells musty. That suggests water is getting in, and EPA says to consider hiring an experienced professional when hidden mold is suspected.^[3]
• You see water stains on the ceiling or wall below the shower. That is a leak, not a grout problem.
• The grout cracks again within months. Movement or a failed waterproofing layer is the likelier cause.

Getting help in Virginia

If the repair grows, read should you regrout or retile your shower and what regrouting costs in Virginia. Loclis lists licensed Virginia contractors; browse home repair or more home repair answers.

When you would rather hand it over, describe the job and local pros will quote it.