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Copernicus18 Aug 2025 22:59Hello everyone,
unfortunately, my bathroom renovation has gotten out of hand.
Originally, I wanted to cover the old tiled splashback with a microcement system (Epodex).
Of course, I first checked the adhesion of the tiles.
After removing two loose ones, practically all of them came off easily.
I thought it’s better to find out now than later and started to level the flexible adhesive.
Unfortunately, I didn’t think it through and used a gypsum-based surface filler (Rotband) for this.
Although Knauf clearly states that it can also be used in bathrooms, I found endless discussions, including here in the forum, advising against it. I believe there is a relevant standard (DIN) as well.
So, what should I do now? The grooves on the wall behind the bathtub are now filled with 3mm (1/8 inch) of Rotband.
My idea to somehow salvage this is to apply a cement-based surface filler over it, then primer, and finally reseal.
Alternatively, I have been advised to remove the affected boards altogether. I am reluctant to do this, especially since they extend behind the bathtub, meaning the bathtub would need to be removed as well…
unfortunately, my bathroom renovation has gotten out of hand.
Originally, I wanted to cover the old tiled splashback with a microcement system (Epodex).
Of course, I first checked the adhesion of the tiles.
After removing two loose ones, practically all of them came off easily.
I thought it’s better to find out now than later and started to level the flexible adhesive.
Unfortunately, I didn’t think it through and used a gypsum-based surface filler (Rotband) for this.
Although Knauf clearly states that it can also be used in bathrooms, I found endless discussions, including here in the forum, advising against it. I believe there is a relevant standard (DIN) as well.
So, what should I do now? The grooves on the wall behind the bathtub are now filled with 3mm (1/8 inch) of Rotband.
My idea to somehow salvage this is to apply a cement-based surface filler over it, then primer, and finally reseal.
Alternatively, I have been advised to remove the affected boards altogether. I am reluctant to do this, especially since they extend behind the bathtub, meaning the bathtub would need to be removed as well…
The approach you suggest—simply covering Rotband with a cement-based filler—is quite risky, even if you prime it beforehand. The core issue remains: Rotband is and always will be an organic-bound gypsum plaster. If moisture gets in, it will inevitably swell and lose strength, regardless of the layer applied on top, standards or not. That’s precisely why professionals clearly advise: No Rotband in splash water areas, not even under waterproofing membranes, unless the manufacturer provides a written guarantee—which Knauf definitely does not do for this specific application.
One point often overlooked in discussions: How thick or deep are the Rotband layers actually, and how far does general moisture penetrate here after every shower? If it’s only a few small repairs and you really stay in a dry zone, as a last resort it might be considered—but behind bathtubs, moisture exposure over the years is usually underestimated. Why risk possible damage later if you can fix it properly now?
Why not just remove it thoroughly and build up a cement-based system instead? It takes a day longer but saves years of worry!
Before you proceed: What waterproofing product do you intend to use (exact product name), and what are your long-term plans for the bathroom? There are definitely differences between waterproofing membranes, liquid waterproofing systems, and standardized installation procedures—that’s an important consideration.
One point often overlooked in discussions: How thick or deep are the Rotband layers actually, and how far does general moisture penetrate here after every shower? If it’s only a few small repairs and you really stay in a dry zone, as a last resort it might be considered—but behind bathtubs, moisture exposure over the years is usually underestimated. Why risk possible damage later if you can fix it properly now?
Why not just remove it thoroughly and build up a cement-based system instead? It takes a day longer but saves years of worry!
Before you proceed: What waterproofing product do you intend to use (exact product name), and what are your long-term plans for the bathroom? There are definitely differences between waterproofing membranes, liquid waterproofing systems, and standardized installation procedures—that’s an important consideration.
H
hanghaus202319 Aug 2025 10:14I once saw a video where someone plastered the entire bathroom with Rotband. Then they painted the shower with epoxy. Done. How durable this is? No idea.
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