Maintaining Limestone Siding | Limestone Siding Maintenance
Limestone siding, like all natural stone, is resilient and beautiful. It will easily last for your lifetime and beyond, and is an excellent investment in your home. It's also largely maintenance-free, meaning you won't have to worry about repainting or restaining it, or be troubled by insects, rot, or woodpeckers. With the exception of earthquakes, which could create some cracks, most natural events that would trouble homeowners with wood or vinyl siding won't pose a problem natural stone is impact resistant, bug resistant, and fireproof. It's also a natural and effective insulator, and is especially high performing in areas with temperature extremes.
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Maintaining Limestone Siding | Limestone Siding Maintenance
However, although limestone siding is tough and durable and relatively maintenance free, it doesn't mean you can go for 50 years without a minor touchup here and there. Like any surface, it will collect dust and dirt, so you'll most likely want to hose it off (gently!) every once in a great while.
Natural stone is also a porous substance and will absorb water which makes it vulnerable to staining (especially from algae). Every couple of years, you should step outside and walk around your house, taking a good hard look at your siding. Do you see any black marks or other signs of stains or discoloration? If so, addressing them as quickly as possible is the best course of action.
Most natural stone surfaces can be cleaned using some form of water, chemicals, or abrasives. For limestone, however, only chemical and water methods are advised due to the relative softness of the stone.
As limestone is an acid-sensitive stone, only alkaline cleaners are recommended. Alkaline cleaners are made from an alkali usually potassium hydroxide, ammonium hydroxide, or trisodium phospate. Even though acidic cleaners shouldn't be used on limestone, alkali cleaners do require a post-wash rinse with an acid (usually acetic acid) to neutralize the surface, followed by a water wash. If you have paint or graffiti to remove, alkali and organic solvent paint removers are effective, and are usually applied with a brush or roller.
For stains usually classified as industrial, metallic, or biological its best to match the removal agent to the stain. One of the best remedies is a solution called a poultice, which will reverse the stain. There are commercial poultice mixes, or you can make your own at home it's typically made with powdered whiting (or some other absorbent material) and hydrogen peroxide or another chemical reducing agent. It's relatively simple to make and/or use, but of course the type of poultice depends on the type of stain. Poultices are applied when moist sometimes even covered with plastic and taped on and left to dry. As it dries, it draws the stain out.
Another company called NaturallyClean™ produces chemical-free enzymatic cleaners that utilize naturally occurring vegetable-based enzymes to eliminate organic stains. These cleaners harness the power of natural cleaning agents and process accelerants without producing fumes or using phosphates and acids. Their NaturallyClean™ Mildew is specifically recommended for cleaning siding.
EaCo Chem's Britenol is an acid-based cleaner designed specifically for masonry surfaces. Acidic cleaners are best used on non-acid-sensitive stones such as granite, slate, and sandstone, but EaCo Chem does recommend Britenol for limestone siding. It is advertised as especially effective under the eaves, where mold, mildew, and algae tend to congregate. (Gloeocapsa magma in particular is an airborne algae that loves limestone, and thrives in warm climates.)
Many historical societies, which have more experience with natural stone siding than your average homeowner, recommend the simplest, gentlest methods first and foremost: Hand scrubbing with a natural bristle brush and water, or maybe a gentle non-ionic detergent.
Non-ionic detergents (also called surfactants) are not soap, but rather made from synthetic organic compounds that are really effective at removing oily soil. Igepal, Triton, and Tergitol are a few of the more well-known brands. Non-ionic detergents also do not leave any visible residue (but you should always rinse your siding after using surfactants).
If the problem area is tough, historians and preservationists recommend spot-testing with chemical cleaners first, as even compatible cleaners (alkaline cleaners are recommended for limestone) can cause damage. Acidic cleaners in particular aren't recommended for sensitive stones (such as limestone or marble), as they can result in etching or dissolution. Even the recommended alkaline cleaners have the potential to damage the stone's surface, hence the spot-testing recommendation.
In all cases, historical societies recommend avoiding any cleaning method that involves pressurization, especially at high levels. Remember limestone is a soft stone. If you must use a pressure washer, using it at 100 psi or lower is best. If you increase the pressure, do so gradually and never exceed 300-400 psi. A low-pressure steam treatment is also an efficient method of loosening the dirt on your siding, and getting plant tendrils to release their grip.
Preservationists also adamantly recommend resisting the temptation of sealers, as absorption and evaporation are natural processes for masonry, and waterproofing treatments can actually cause moisture to become trapped, causing even bigger headaches down the road. Even the Brick Institute of America notes that, "the most efficient and low-cost method of damp-proofing or waterproofing walls is proper construction."
Tips for Effective Water Cleaning
Water is the safest method by far, but there are still important safety considerations. First, you need to be sure your joints are sound. If your siding isn't watertight, you could have problems.
Never clean during or before cold weather! If the absorbed moisture freezes (and it could take more than a week for your masonry to dry), it'll crack your siding.
Even if you use a really low psi setting, you need to be aware of other factors, such as the distance from the nozzle to the stone, type of nozzle, and the gallons per minute (gpm). Even a low setting could damage your limestone siding, which is why non-pressurized cleaning is generally recommended.
What's in your water? Many municipalities have naturally occurring minerals and additives (such as fluoride) in the water supply. Iron and copper can cause discoloration, for instance, unless a chelating or complexing agent is added. This agent inactivates metallic ions, softens minerals and water hardness, and prevents staining.