The Proper Way To Clean & Seal Exterior Slate or Flagstone
Material: Flagstone: Exterior Patio: Approximately 2000 sq/ft
Customer Request: Bring out the color of stone without adding any shine.
San Diego Stone Care Exterior Stone Recommendations: The number one observation I see on almost every exterior stone application is what I consider, not necessarily the wrong sealer, but the wrong type of sealer that will cost you $1000.00’s of dollars to maintain over the years to come, applied to exterior stone applications. The reason I say it’s not the wrong sealer is because when these types of sealers are used on interior stone they usually work beautifully with no problems.
First, let me describe the type of sealer that is usually applied to exterior stone & why… and then I will describe the type of sealer that I recommend, which will not only make your patio areas look beautiful, but the sealer application will last longer & it will be less expensive to maintain over the long haul. The type of sealer that is usually applied is called a “Topical or Coating Sealer” which performs just like it sounds. When you apply this coating sealer some of the product does absorb into the stone and some of the sealer lays on top of the stone. When you apply more coats you are building layers on top of the stone…hence you are making a protective layer of sealer that sits on top of the stone…OK that sounds good so far right? In addition, especially as you add more coats the sealer will leave anywhere from a matte to a high gloss shine, which I know a lot of people like that look. Now these coating sealers also bring out more detailed color of the stone. The reason you see these coating sealers on almost every exterior stone installation, I believe, is because of this. Exterior stone installation is quite often done by a landscape contractor not a tile contractor & this is just fine I have seen some beautiful installations. But for whatever reason landscape contractors seem to like using these coating sealers, maybe because these are the same sealers they use to seal stamped and colored concrete for protection, and what is good for the goose is…well you know the rest. (By the way you will have same issue with your stamped concrete with these coating sealers but these coating sealers are the only thing that will protect your concrete…not true with natural stone)
Where is the Problem? A couple areas: One the fact that they are a coating and shiny can present a problem of being slippery especially when water, like in pool areas, gets on top of the stone. Secondly…UV sunlight & water both affect coating sealers in a negative way; actually sunlight makes all sealers less effective over time. But the real problem is water not only when you have standing water, like after a rain or from ones sprinklers, but also water that is below the stone…underground. You see coating sealers act like a lid on a can of paint, although many manufacturers state their sealers are breathable…this is not enough to prevent water vapor damage…so water that comes from below the coating is now trapped and begins to deteriorate the sealer. You will know this is happening, especially around the edges of your patio or areas where there is not much sunlight, because your stone and sealer begin to take on a white opaque look to it. So…we will get the call when someone sees this and they say: “My stone needs to be cleaned” Sorry…but cleaning alone is not going to fix your permanent problem. Last and the biggest & most expensive problem…what needs to be done to fix this damage? Can I just add more coatings to improve the look…yes you can but you will not improve the look. You will only make a damaged patio look shinier. Can I just patch apply sealer to the most damaged areas…yes you can & you will have the same results a shiny damaged looking stone.
The San Diego Stone Care Solution: The only solution which will bring back your stones original look is to strip off as much of the old coating sealer as possible, which is a time consuming, costly process. Why? These coating sealers require using very smelly dangerous & costly stripping solutions, by hand, one tile at a time, to remove as much of the coating sealer as possible. (You will never remove all the sealer as some will stay trapped below the surface of the tile.)
So once you have all the coating sealer off the stone and it has been allowed to dry properly…now we can apply a much better longer lasting “Penetrating Enhancing Sealer”. (If you have a new installation that has not been sealed yet this is an even a better situation to have.) How is this “enhancing sealer” different? First…it’s a penetrating sealer, which means, it is absorbed, into the stone and grout and protects the stone from below. (There is no sealer left on the surface of the tile….If there is any sealer residue on top of the stone, your stone care company incorrectly installed the enhancing sealer…we see this almost every week…please let San Diego Stone Care do your stone maintenance!) Second…the sealer also “enhances the natural colors” of your stone WITHOUT adding any shine…this is a good thing – no slippery stone) . What makes the enhancing sealer a better sealer application? Although every sealer is affected by the suns UV rays, penetrating sealers seem to last longer than coatings since they are below the surface verses coating sealers which are more exposed to UV since they sit on top of the stone. Also…penetrating sealers are a better breathable sealer…which means these do not trap moisture that comes up from the ground but allows the water vapors to transmit safely through and out the stone and grout. (No white hazing looking tiles) Lastly…enhancing sealers do not need to be removed at all in order to re-apply more sealer down the line and they do not need to be applied as often as coating sealers to be effective. So re-applying enhancing sealer in the future is as simple as giving you stone a good cleaning, allowing it to completely dry, and re-applying the enhancing sealer. This is actually easy enough that with some direction from me some of my customers re-seal their own patios. (I would doubt any customer would want to attack removing a coating sealer…we don’t even like doing it.)
FYI…there are also “Clear Penetrating Sealers” which perform exactly as do the enhancing sealers except “Clear Sealers” do not add any color to your stone or grout…If you like how your stone looks without any sealer then a Clean Penetrating Sealer is the right sealer for you.