At first we thought this product was a 'God sent'. However, with repeated use we have found that it has begun to completely eat away at the grout between the tiles and between the tiles and tub in our tub/shower area. Looking forward now to the job of cleaning out all remnants of the product from between the tiles and regrouting the affected areas...not pleasant. Just got a subscription renewal shipment (as yet unopened box), only to discover the issue of the grout being eaten AND the fact that the product (unopened case lot) is not returnable to Amazon. Very disappointed. Recommend use only un ungrouted surfaces, a high end tub tile job will not stand up well to this very harsh product.