A few simple cleaning and maintenance steps can help your keep your sandstone patio looking good for many years. Sandstone is an easy-care patio surface. But don’t get in the habit of letting things go until nature takes its course. It’s much more difficult to clean and restore outdoor sandstone once dirt, grime, mold, algae and weeds have settled in.
Sandstone, sometimes generically called flagstone, is flat sedimentary stone primarily made up of feldspar and quartz. Different regions are known for unique sandstone colors. Sandstone is porous, and sandstone rock formations filter -- purify -- and store water well as aquifers. Flat blocks of quarried sandstone are split into thin layers and used for both interior and exterior applications in homes and businesses. Slabs can be broken into irregular shapes or cut into uniform concrete-style pavers. Sandstone has a naturally nonslip surface, which makes it ideal for floors and pavement.
Sweep your sandstone patio regularly, and hose it off occasionally. Dirt particles can drift into sandstone pores and start to darken and discolor the surface over time. If leaves fall onto sandstone and remain during rainy weather, the surface can stain. Rake up and remove leaves frequently. Make sure all surface drains are in working condition and clear so rain or irrigation water runs off quickly. Also maintain rain gutters and downspouts to prevent overflow downpours onto your patio.
In wet climates or where humidity is high, mold, algae and eventually lichen may grow on your sandstone pavers. Clean these and related organic stains quickly. Chlorine and water or chlorine-based commercial cleaners do the trick, but chlorine is an environmental toxin. Thoroughly wet the stone surface and try a 50-50 vinegar-and-water solution first, scrubbing a small test area with a brush. Mild detergents may also work. If you clean with chlorine bleach solution instead, sponge up the scrub water and dispose of it via your household plumbing rather than through storm drains, for proper treatment. Avoid pressure-washing, which can abrade and damage sandstone surfaces.
Sealing outdoor sandstone is a subject of some disagreement. Many stone installers don’t recommend it, because in heavy weather sealers can actually increase staining and discoloration problems. If moisture enters pavers from below it can’t escape, and may cause white mineral film to develop beneath the seal. The argument for sealants or sealers -- especially for sandstone used indoors -- is self-evident: They help seal porous stone against oil, greasy spills and embedded stains. Natural-look subsurface sealers are the best to use on sandstone if you do choose to seal your pavers. These sealers, called impregnators, allow the stone to “breathe” somewhat, so moisture vapor is released yet water isn’t deeply absorbed. Reapply sealers every 18 to 24 months.
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