Should I use 100% Silicone Caulk Sealant or the Sanded Caulk Sealant?


I have a white subway tile backsplash in my kitchen, counter is granite. Should I use 100% silicone caulk between the two or can/should I use a sanded silicone caulk by the same manufacturer??


ANSWER - The tile and stone industry standards require that an ASTM C920 sealant (caulk) is used for movement joints and transition joints between changing planes or materials.  ASTM C920 are normally 100% silicone or a urethane sealant.

Sanded sealants (caulking) normally do not meet ASTM C920 standards nor do they perform as well or last as long.  Typically sanded sealants are acrylic or latex based and they might say it is siliconized, which is not the same as being 100% silicone.  They are much easier to use for the installer in terms of application and installation, but they don't come close to lasting as long or performing as well.  Installing the 100% silicone sealants requires much more protection and care, and timing of the application is critical to ensure a good installation and easy cleanup.

I have seem some installers broadcast sand over the 100% silicone so it looks more like the grout, but that diminishes the performance of the material and voids the product warranty.

Note that per the sealant directions you are suppose to apply a backer rod or backer tape in the movement joint before applying the sealant, and the sealant needs to be at least 1/4" thick for walls, which isn't practical for very thin tiles.   Per sure to follow the sealant manufacturer's directions.

20 thoughts on “Should I use 100% Silicone Caulk Sealant or the Sanded Caulk Sealant?

  1. Rob H says:

    I used “Custom” brand Sanded Ceramic Tile Grout to redo cracking grout on the bottom of my shower where the floor meets the wall. Do I need to also use a sealer or is the grout enough? The grout is siliconized, but Not 100% silicone

    • Donato Pompo says:

      A sanded grout is normally a rigid cementitious grout and it should never be used at the transition from the floor to the wall.

      You said it was siliconized, so that suggests it was a resilient caulking, but not one that meets ANSI C920. The 100% silicon caulking/sealants do meet ASTM C920 and will last a lot longer. The siliconized caulking will work at first, but they don’t last as long or perform as well.

      Regardless of which sealant/caulking you used, you don’t need to apply a sealer over it as the caulkings in theory are impervious.

  2. Sarah says:

    What about silicone first and then sanded silicone… just for looks? Would that do meet the code requirements?

    • Donato Pompo says:

      I have tried adding sand in silicone and urethane sealants and it doesn’t last long or perform well. And it would not meet the industry standards.

  3. Aaron says:

    Great info! I started to use sanded to patch some cracks and this stopped me.

    I have a shower with marble hex tiles and standard grout. The grout has gotten a bit dirty (I don’t think it was ever sealed), and I was thinking about cleaning, then using a 100% silicone over the old standard grout. Is this a bad idea? Haha. I like the longevity and resistance to mildew/mold that the silicon provides.

    • Donato Pompo says:

      You need to get enough depth in the grout joint for it to be practical to over fill the joint with the ASTM C920 silicone sealant. The grout joint and the sides of the tile have to be very clean. You might need to use a primer first.

      Make sure you use a silicone sealant that is mildew/mold resistant. Don’t use a clear sealant as they tend to darken. When you apply the sealant you should tool the joint slightly to give a slight concave surface so that feet don’t walk on the sealant. This will help prevent the sealant from getting dirty that can be difficult to clean.

  4. Mike says:

    I’ve used GE Advanced Silicone (100% silicone) on the joints in my quartizite countertop and it has cured with a gloss surface. Is there a way to degloss it?

    • Donato Pompo says:

      If you try to roughen the sealant up it will have more of a tendency to collect dirt and will be more difficult to clean. The gloss surface is better and more practical.

      • Brian says:

        I am facing this glossy dilemma right now. We just had black uba tuba LEATHERED granite installed. They are cutting all but one backsplash to install next week, but they did seal one backsplash piece to the countertop. Is there not a matte solution or a way to de-gloss the shiny silicone?

        • Donato Pompo says:

          It is normal that the silicone sealant has a slight sheen. Most silicones can’t be painted, but there are certain ones designed for painting over. So you could paint over with a flat paint, but I doubt it is worth the trouble. There are polyurethane sealants that don’t tent to have a sheen, but it could be problematic for the stone fabricator. I would just live with it.

  5. Norm says:

    We have quantize counters with a small waterfall backsplash in back of sink. A gap between the counter top and the bottom of the the water fall has begun to form. The silicone is separating. I removed silicone and than noticed there was some type of grout beneath the silicone, between the counter stone. As I removed the clear silicone the the grout behind it was coming loose also, so I removed that also. I think it is “Sanded Silicone”? Can I cover Sanded silicone with clear 100% silicone?

    • Donato Pompo says:

      Per TCNA EJ171 industry standards, at all change of plains should be a resilient movement joint as there is likely to be movement at those transitions. We call it a movement joint.

      Sanded sealants (caulking) normally will not meet ASTM C920 requirements that should be used. It will perform as well and won’t last as long.

      You should remove all of the material in the joint. Clean the joint out. If the joint is at least 1/8″ wide and over 1/2″ deep you can install a 1/4″ diameter polyethylene foam back up strip. Push it down at least a 1/4″ and then fill the joint with an ASTM C920 100% silicone or polyurethane sealant. These sealants are more difficult to work with. So you should apply painter’s tape one both sides of the joint tightly to the stone surface. Fill the joint with the sealant and then tool the excess off leaving a slight concave finish. Immediately pull the painter’s tape and you will get a nice clean joint that isn’t messy; unless you loose control over the tape you removed that has the excess sealant on it.

    • Donato Pompo says:

      I don’t think there could be any significant difference between Mapei’s 100% silicone sealant and other brands. Silicone sealants are more difficult to work with and more messy if you don’t know what you are doing, but they perform much better and longer than acrylic sealants.

      When installing silicone sealants, you need to put painter’s tape on both sides of the joint tight to the tile surface. After you apply the sealant so it fills the joint and oozes out the top, you scrape off the excess and then tool the joint to a slight concave finish. Then immediately pull the tape off pulling away from the joint. If you do that you get a perfect sealant joint without a big mess.

  6. Allan says:

    What are your thoughts on using color matched, sanded caulk that specifically says it meets ASTM C920 requirements? I ordered it online, and it’s more expensive due to shipping, but in theory provides the best look and necessary flexibility.

    • Donato Pompo says:

      I have never heard of a sanded ASTM C920 silicone or polyurethane sealant. I would read the data sheet wording carefully. It might say it meets ASTM C920 in certain ways.

      Sanded caulking is normally a latex based type of sealant that is easier to install and clean up, but is not long lasting nor does it bond as well to the materials substantially.

      I have experimented years ago with ASTM C920 sealants and added sand and it didn’t perform well or last long.

      By adding the aggregate to the sealant it limits its ability to expand and contract. Maximum performance is with a true ASTM C920 sealant. After it is installed for awhile you will likely not be able to tell the difference.

  7. Erica says:

    After 5 years from install, My “Custom” brand 100% silicone caulking in my shower has mold behind it. The epoxy grout has fine cracks in it in the shower pan. An outfit came out and wants to re-do the shower pan and states that if done right, the caulking should never have mold behind it, meaning never, and the grout should never crack between the tiles. Is this the case? or is it standard to have moldy caulk that needs replacing as it eventually fails which I keep seeing on the internet? And if so, is all that needs to be done is some touch-up on the grout and re-do the caulking after killing the mold?

    • Donato Pompo says:

      I have seen where clear silicone caulking can discolor. Whether it is a microbial stain or not would have to be determined by testing. The silicone itself doesn’t support or perpetuate microbial growth, but if there is organic food behind the sealant with moisture it can develop and show through.

      The cracks in the epoxy grout on the shower floor is a symptom of a problem. The problem could be that there is excessive deflection the floor or it could be the epoxy grout wasn’t installed correctly. The only way to know for sure is to forensically remove tiles and evaluate the underlying conditions. If there is an waterproof membrane under the tile as there should be, slight cracking along the edge of the tile between the epoxy grout probably doesn’t cause a problem.

      You can remove the silicone caulking and reinstall it. There should be a closed-cell foam backer rod or bond breaker tape behind it, which is often left out. You could replace the caulking with a colored sealant and make sure there is a backer rod or tape. If the condition behind the sealant doesn’t change then it might develop microbial growth, or the foam backer rod might created a barrier to sealant, if that is what caused the stain, but with a colored grout and foam backer rod you probably won’t see a stain.

  8. Erica says:

    Thank you so much for all of the info on this situation. The shower pan is 5 1/2 X 4 feet with a linear drain in the center that is 42 inches long. The tiles are 22 x12 inches. So seems to be large tiles for a small space. Would this contribute to a deflection problem?
    Tiles have a texture and we have iron in our well water, which is difficult to clean off. I tried barkeeper’s friend cleanser and it seemed to have taken off the surface sheen? Their website claims that the cleanser will not damage the surface and is perfect for getting off iron deposits. The Schluter 42 inch long linear drain is a huge hassle as the water just sits in the trough and needs cleaning once a month. Why would one want to clean out a huge shower drain once a month???
    So with all of this, I think that my best bet is to pull up the pan tiles to see what may be going on behind regarding the mold issue, and find a replacement tile that has a smoother surface to eliminate the iron problem, find a small round 4 inch drain that does not need monthly cleaning, make sure that the caulking is installed correctly. Or may I ask, I have a slab on-grade house including the shower, why can’t I grout all of the joints instead of caulk? A number of folks told me that the walls and floor still move even if this shower is sitting on a concrete slab, with just contraction and expansion of the surfaces from heated shower water and cooling.

    • Donato Pompo says:

      Using larger sized tiles in smaller spaces makes the space appear larger, although normally shower floors will tend to use smaller tiles that provide better slip resistance and are easier to installer in some cases where there drains in the middle of the floor.

      Trench drains are great because they are easy to clean and prevent clogging. With a smaller area drain much of the debris that causes problems get into the plumbing that can cause problems. What isn’t normal is to have the trench drain in the middle of the floor. Normally it is installed on the back wall so water is draining in only one directly away from the entrance. Plus the bottom of the trench drain should have a slope to the drain outlet so water doesn’t collect.

      Sounds like you might have a natural stone that has discolored and etched. If it was a porcelain tile it wouldn’t stain. If it is a natural stone, it should be able to be refinished by a professional stone restoration company to look like new.

      Per industry standards, all transitions in the shower should be filled with an ASTM C920 sealant/caulking that not only will mitigate movement, but it makes those joints water tight.

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