A dark color has been formed on a part of our Balcony floor, probably because of the rainwater remaining due to the blocked balcony drain.
I'm looking for strong liquids to clean it up, now that Coop DIY etc. are again open. I appreciate any recommendations and experiences of working solutions.
Can you post a picture? If you put harsh chemicals on your balcony and rinse it, those chemicals will rinse into the garden of your neighbor below. Also it's a nice courtesy to warn the neighbors below if you're going to be doing some enthusiastic cleaning, so they can move patio furniture and close windows as needed.
If water running to the neighbour below is no issue, the I would water blast it as the first no chemicals solution. If you do use chemicals, then keep the volumes low. Any excess is wasted and can only cause problems. Mould cleaner is highly basic - much cheaper if you buy washing soda (Sodium carbonate) from the drogerie, washing soda is stronger than baking powder. Adding vinegar produces bubbles and enhances the lifting effect but neutralises the base, so add the vinegar after an hour. The harsh chemicals have the benefit of killing mould spores.
If water running to the neighbour below is no issue, the I would water blast it as the first no chemicals solution. If you do use chemicals, then keep the volumes low. Any excess is wasted and can only cause problems. Mould cleaner is highly basic - much cheaper if you buy washing soda (Sodium carbonate) from the drogerie, washing soda is stronger than baking powder. Adding vinegar produces bubbles and enhances the lifting effect but neutralises the base, so add the vinegar after an hour. The harsh chemicals have the benefit of killing mould spores.
I was also going to suggest using a power-washer. I used one recently on the stone tiles of our patio and was amazed at how well it removed everything, including all the mold, etc. from the concrete. It looks like I have a brand new floor out there. The kind I used required a hose hook-up, though (which wasn't a problem since we have a hose in our garden). But I assume you don't have a hose on your balcony, so you would need the kind of power washer that allows you to fill it with water first (unless you ran a hose from your bathroom or kitchen faucet using an adapter).
If you do decide to try a power washer, there is a nice site that allows you to rent various machines and tools from people in your area. Looks like there are some power washers on there for around 10 CHF per day or more.
I have been looking into buying a power washer, and was wondering exactly that: Are there models that you can fill it with water, rather than have the direct connection? I do have a way to run a hose from my kitchen, but, I hate doing that as its never convenient to unscrew/rescrew and there's always a bit of leakage.
Any idea of brands, models, where to look for that fit the bill?
I have a kaercher. Since I have a large terrace with a water outlet, it’s no problem. I don’t know if there are ones you fill up, they use a lot of water. A steam cleaner might be feasible - you fill them up and either connect to electricity or there might be battery operated models.
in a liter of water, leave to soak of the tiles for a couple of hours and then kärcher it with tap water. If you are lucky the washing soda may do the trick without water blasting.