Bathtubs are not meant to be storage areas for construction debris, tools, or building materials. Yet walk into many new homes under construction or bathroom remodels and you will find bathtubs brimming with all manner of debris: paint cans, thinset, drywall joint compound (known as mud), grout, mortar, garbage, empty coffee cups, and tools.
Unfortunately, some contractors find bathtubs to be a convenient enclosed area in which to store, contain, and spill their debris. One reason why they do this is because new bathtubs sometimes come lined with protective plastic coating, seemingly rendering the surface safe for debris. Most contractors and trades do not do this, and they hate hearing about this even more, because it stains the reputation of their profession.
It is bad enough to find trash in the tub. But as long as the surface is not scratched, trash can always be removed. It is an entirely different matter to remove that trash and, underneath, find large, dried clumps of grout, mortar, or drywall compound. What are your options when your tub is coated with any of these materials?
Cleaning Drywall Compound
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 exponentially more difficult.
If you were cleaning drywall tools, you would hit them with hot water and scrape them off with another drywall tool. But with a delicate tub surface, you do not have the luxury of scraping with a metal blade.
After removing the debris from your tub, fill the tub with soapy hot water and let the water sit for about 30 minutes. Drain the tub. Gently scrape with a plastic paint scraper, the edge of a discarded credit card, or a plastic hotel key.
Often, the water will work underneath the drywall compound and the entire chunk will loosen. Other times, the compound remains glued to the tub surface. The water will soften the top layer of the compound. You can work on that top layer with the scraper or with a Scotch-Brite pad. You may need to take multiple passes at the dried-on mud. After you scrape off the top layer, you expose a hard lower layer. This hard layer will need another long soaking in hot water. You may need to repeat this process several times until the mud is fully gone.
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.
Cleaning Grout or Mortar
For tile grout or mortar, removal will be more difficult and damage to the tub surface may occur. Grout and mortar are not water-soluble, so the soak-and-scrape method (as you might do for drywall compound) will not work here. Expect that some damage will occur. Your aim, then, is to minimize the damage.
Tile grout is very abrasive. Leading manufacturer of tubs and showers American Standard recommends using a wooden popsicle stick or tongue depressor to remove tile grout. You can also purchase inexpensive plastic scrapers from a paint store or home center.
In addition, when you push against the grout or mortar, try to avoid scraping the material across the surface any farther than is necessary.
Avoid sweeping up fallen grout and mortar debris, as this may lead to scratching. Instead, suck it up with a shop vacuum.
When all is done, use granular Spic and Span mixed with water to clean off the remainder. Alternatively, you can use a kitchen-grade Scotch-Brite pad. Avoid Scotch-Brite Heavy Duty pads, as these are intended for outdoor items like grills and garden tools.
Finally, if you do end up with any dulled areas, they can be restored by rubbing with a white automotive-type polishing compound and waxing with a liquid wax.