- 1). Mix the acid crystals exactly as the manufacturer instructs. Phosphoric acid substitute can be used instead of sulfamic acid if the latter is unavailable.
- 2). Drip the acid solution onto the thinset in the shower floor, using a sponge. If the spots of thinset are small, use an eyedropper. Discard both the sponge and eyedropper after using them with acid.
- 3). Agitate the acid on the thinset, using a hand sander or power scrubber on the lowest setting. The acid will react with the Portland cement in the thinset and cause it to break down. Continue grinding at the thinset until it completely comes off.
- 4). Wash the floor with water. Do not leave the acid to dry on the shower floor as it can damage the tiles. Dry with old cloths or rags after rinsing the crumbled thinset and acid off.
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