How to Remove Grout, Mortar, and Drywall Mud From a Bathtub

Construction debris in bathtub presents special difficulties when it comes time to clean the tub
Phillip Stewart/Flickr/CC BY-SA 2.0

Bathtubs are not meant to be catch-alls for construction debris or building materials. Yet walk into many bathroom remodels or new homes under construction and you will find bathtubs brimming with all manner of debris: paint cans, thinset, drywall joint compound (known as mud), grout, and mortar, among other detritus. If you're a DIYer, you may have recently re-tiled or regrouted your tub but forgot to mask off the tub itself, and now you have dried, rock-hard blobs of grout and/or tile mortar stuck to the tub surface. The good news is that all of these things will come up; it just takes some elbow grease—and some care to prevent scratches.

Removing Drywall Compound From a Tub

Drywall compound, or mud, is water-soluble. Unfortunately, the mud is not as water-soluble as you might hope. It will not magically dissolve the instant water comes into contact with it. You still need to work at it. In fact, painters and drywall contractors religiously clean their tools the instant they finish using them, far in advance of the mud drying. Once the mud has dried, it is still possible to remove it, but it becomes a lot more difficult.

  1. Fill the tub with soapy hot water and let the water sit for about 30 minutes, then drain the tub.
  2. Gently scrape off the dried blobs of drywall with a plastic paint scraper, the edge of a discarded credit card, or a plastic hotel key. Because drywall compound contains silica, quartz, mica, and gypsum, it is an abrasive material. While it is not as abrasive as grout or mortar, you should still be careful when scraping away the mud. Avoid long strokes that move the mud beyond the affected area.
  3. If the compound remains glued to the tub surface, scrape off the top layer that has been loosened by the water. You can also scrub with a non-abrasive Scotch-Brite pad.
  4. Remove dried pieces by hand so they don't wash into the drain, which can lead to clogs.
  5. Repeat the same process, as needed, to remove all dried mud and residue. Rinse the tub thoroughly.
  6. Restore areas where the mud has dulled the finish by rubbing with a white automotive-type polishing compound, then wax with a liquid wax.

Cleaning Grout or Mortar From a Tub

Tile grout and thinset mortar are cement-based materials and are more difficult to remove than drywall mud. Grout and mortar are not water-soluble, so the soak-and-scrape method (as you might do for drywall compound) will not work here. Also, grout and mortar are gritty and can scratch the polished surface of a bathtub. Therefore, in addition to removing the mess from the tub, your aim is to minimize any damage.

  1. Use a wooden popsicle stick or tongue depressor to carefully pop off dried blobs of grout or mortar. You can also use an inexpensive plastic scraper from a paint store or home center.
  2. Collect loosened pieces of grout or mortar as soon as they come free, and be careful not to let them slide across the tub surface, which can lead to more scratches.
  3. Remove all grout and mortar dust and small particles with a shop vac. Do not sweep up the debris, to prevent scratching.
  4. Mix Spic and Span (or a similar non-abrasive cleaner) with water in a bucket. Scrub areas of discoloration with a non-abrasive sponge or scrubber dipped in the cleaning solution. Rinse the area well, and repeat, if necessary.
  5. Polish dulled areas with a white automotive-type polishing compound, then wax and buff with a liquid wax.

Removing Tough Grout or Mortar Residue

The cement in grout and thinset tile mortar can leave set-in stains in almost any surface, including tubs. If you've tried scrubbing with a cleaning solution and a sponge or scrubber, but the discoloration remains, another thing you can try is a commercial grout haze remover.

Grout haze removers are designed to remove the whitish haze that forms on the faces of tile after the grouting process, but they can also help with grout stains. Apply a grout haze remover according to the manufacturer's directions. Usually, this involves wiping with a paper towel or a clean rag. If that doesn't do the trick, you can try a Mr. Clean Magic Eraser, along with the remover product.