I have tried high pressure hosing the dirt build up. It needs extra abrasion though to fully clean. too much to do manually. Is there a machine I can hire?
Welcome to the Bunnings Workshop community. Thank you so much for joining us and sharing your question about cleaning your terracotta tiles.
I suggest using Chemtech 5L Brick Tile And Paver Cleaner. This is one of the most popular cleaning agents that builders use. Please read the instructions before using this product it will need to be diluted before use. I recommend testing the cleaning agent in a hidden spot to make sure that it is compatible with your terracotta. I propose using an Oates Compact Deck Scrub Brush in combination with a Ryobi 2000W 2200PSI Pressure Washer using the deck and driveway head cleaner.
Due to the time that it has been exposed to the elements, it will never have the same finish as it did when it first got laid down. The best we can hope for is a much cleaner surface. Discoloration and sun damage can't be washed off.
If you need further assistance, please let us know.
Thanks guys. Seemed a plausible plan, but didn't quite hack it even when using the cleaner neat. I've high pressure cleaned which gets the slimy stuff off but the ingrained dark patched just sit there! I can abrade it out with a sander - but rather a lot of work. Bleach? Appreciate your effort.
Are these tiles sealed @SteveHoptroff? Place some droplets of water on their surface. If they don't absorb within 15minutes, there's a sealer on them. If there is a sealer on them and the pressure washer isn't blasting the grime off, then the contaminants have embedded into the sealer. You'll need to remove the sealer with an appropriate stripper suitable for the sealer that was used and then re-seal them.
I'm getting the impression that the tiles are possibly sealed from your description of them needing to be abraded.
We had the tiles high pressure cleaned and sealed "professionally" some years back. The idea being the sealer make it easier to clean the tiles after sealing. This didn't work too well. Tried your water test. Where I abraded the water is immediately absorbed. Elsewhere it just sits there so your assumption seems correct.
How to remove sealer?
Then clean and reseal? Thanks.
The two main types of sealers are penetrative and surface, Steve (@SteveHoptroff). You'll need to work out which one of them was used. Diggers 1L General Purpose Lacquer Thinner applied to a test section should start to eat away at a surface sealer. If not, you likely have a penetrative sealer. Since you can abrade the surface, and then the water absorbs, it's a pretty good indication that it is a surface sealer. You can also try using Diggers 1L Xylene Solvent, Crommelin 1L Water Rinseable Degreaser and Crommelin 1L DiamondCoat Solvent. A stiff bristle broom can be used to agitate the solvents and a scraper to scoop up the coating off the tile surface into a bucket. These are all pretty potent chemicals, and all appropriate PPE gear should be worn including a respirator, goggles and solvent resistant gloves. A penetrative sealer will take several goes at applying the solvent to get enough of it out of the tile to allow a new coating to adhere. Please make sure to start with a test section before moving onto the entire area, as discolouration of the tiles could occur.
Stripping sealants off tiles is a laborious and time-consuming task, so much so that I'd encourage you to get a few quotes to see how much it would cost for someone else to do it.