This was a beautiful house to work on. Being renovated and prepared for market, it was all go to get this place looking amazing.
We were hired by the builder that was performing the renovations. The majority of what we worked on was real slate, natural Travertine and natural Marble. We love working with a product that we know is going to look fantastic when it’s cleaned, so we were happy to take on this project.
The builder was sealing the stone themselves, using high-end decorative sealers, so it was our job to not only clean the surfaces, but to prepare them for sealing as well. This means no enduring post-treatment or other chemical residue, a perfectly clean surface and a mild etching that wont damage natural stone, which is the hardest bit.
We took a tiered approach to cleaning the stone. We started with a typical pre-treatment of Potassium Hydroxide and Sodium Hypochlorite. We gave this one a very thorough soak and gave it a fair amount of time to work. We then pressure cleaned all the surfaces with a combination of surface cleaner, turbo nozzle and fan tips. Pretty standard stuff. Instead of applying a Sodium Hypochlorite based post-treatment which we would typically leave on a surface for restoring as much brilliance as possible, we went a little more specialist on this one. We needed to prep the surface for a semi-coating sealer, but natural stone is very sensitive to acid, so we couldn’t give it a standard Hydrochloric Acid etch. We used an organic amine salt based acid substitute in a weak solution across the whole area. Because it’s an oxidising agent, it will bleach the surface, which is why we used a weak solution and used it evenly across the whole area.
There were quite a lot of rust stains across the whole property. For these we used a combination of Oxalic and Phosphoric Acid (not at the same time) to remove rust and other iron stains such as fertiliser etc. We would then blend those areas in with a progressive amine salt solution, to smooth out the gradation between the lightened area and its surrounds, knowing it would even out even further once having the decorative sealer applied.
This was quite a large job, so we did it across two days. That gave us the option of working in stages, where we could leave pre-treatments actively working in one section while we cleaned another. We were even able to leave a treatment on overnight to get the effect of a post-treatment, with the ability to remove all chemical residue the following day.
The trickiest bit of this project was that there was a previous coating sealer which still had some residue on the slate. A full chemical stripping was out of scope and out of budget. Stripping requires working in very small, workable sections and would have turned this from a large project into a gigantic one with huge cost.
What we did instead was blast any obvious sections with a turbo nozzle. We then conducted a test patch of applying sealer that had been very heavily thinned with Xylene (the sealer was solvent based) as an undercoat. Xylene is a very aggressive solvent, so we were testing to see if it would re-work the remnants of the old sealer into the new undercoat. We love it when a good plan comes together and this was one of those times. Xylene is very expensive, but not as expensive as a high quality slate sealer, so it’s often helpful to do this anyway, as it provides for better coverage on the undercoat, rather than undiluted sealer being wasted by being sucked into the substrate. It provides for more economical coverage across two coats.
We just wish we had been back to this one, once it had been sealed.