What thinset, grout to use when installing new tile in a spa?


Installing Tile in Spa or Swimming Pool - I am in the process of installing new tile in the spa. some of the tile will be in water, the bottom of the spa is plaster.

I have consulted with employees at several stores with a very conflicting amount of installing information and products to use.

I would like the job done right the first time! I have installed tile on floors but this has to be water proof.

The spa is in the down stairs bath, in the ground, with plaster. I have removed the tile and it looks like a gray thin set was used. It was attached to wood and cement. The old tile lasted 15 years but the grouting and some of the tile came loose. I wanted the new tile so I tackled the job.

What kind of thin set and grouting should I use. My new tile is in sheets. What color grouting and does this come in mixed or do I mix with a special glue used for grouting and thin set?


ANSWER - I will assume the spa surface will be a plaster material.  You mentioned something about wood, but never install directly over wood in a wet area.  Whether you are tiling the whole spa or just at the water line, I would recommend applying a liquid waterproof membrane first over the properly prepared clean and sound plaster surface.  Laticrete has one called 9235 Waterproof membrane and Custom has one called Red Guard and there are others.  Go to Installation Products for their website links.

The membrane will provide some protection against efflorescence (leaching of salts and plasticizers from the plaster on to the surface of the tile) and shrinkage cracking. Then use a polymer modified (multipurpose) or latex modified thin-set that is recommended for swimming pools to adhere the tile to the membrane. Read the bags or data sheets to be sure, but most good quality products will work under water, although some won't!.  Use white thin-set if you are using white grout, so the thin-set doesn't show through the grout.  You can use polymer or latex modified grout, which will work fine, but for maximum protection use an epoxy grout.  Epoxy grout is more difficult to use and more expensive.

Be sure to follow the instructions from the manufacture of each product you use!!!

Good Luck!

28 thoughts on “What thinset, grout to use when installing new tile in a spa?

  1. Mike Palladino says:

    I’m tiling my pool and using a porcelain pool tile what size grout lines would you have 1/8 “, 3/16 or 1/4” thank you for your info.

    • Donato Pompo says:

      Typically porcelain pool tiles come as sheets where they are glued to a fiberglass web so the grout joints are pre-set which is typically 1/8″ wide. Mosaic glass tiles will come mounted with 1/16″ wide grout joints which is the minimum width that is allowed. You can make the grout joints wider, but the more grout exposure the more cleaning that might be needed.

    • Donato Pompo says:

      I will assume you have an all-tiled pool that is leaking. Grout is not a waterproof material unless it is an epoxy grout or an ASTM C920 sealant caulking. Even then they are not rated as waterproof in terms of justifying eliminating a primary waterproof membrane that the pool should have.

  2. Samantha says:

    Hi Donato! I am using an unglazed porcelain tile (Corso Italia Alpe Graphite 12×24, outdoor use) as my pool decking. I am interested in continuing the same tile over the edge of the pool onto the stairs, baja shelf, and waterline. Then finishing the remaining pool walls and pool bottom with a different, more standard pool finish. I’m curious whether this is possible? Is there some sort of protective layer such as epoxy that can render the pool tiles pool safe? Thank you so much in advance.

    • Donato Pompo says:

      Porcelain tiles are commonly used in swimming pools including all-tiled commercial Olympic pools and all-tiled residential high-end pools as well as tiles used on waterlines and spas.

      The submerged tiles on the steps and shelf can be directly bonded to the gunite/shotcrete concrete surface after properly preparing them. If it were an all-tile pool you would first install a waterproof membrane over the shotcrete and/or mortar bed. Make sure the thin-set mortar adhesive is recommended for submerged applications.

      If you are installing the tile over a spa cap and around the walls and spill edge they should be waterproofed first with one the tile waterproof liquid applied membranes. If you don’t then you are likely to get efflorescence staining; not the surface type from the evaporation of the water as it goes over the spill way, but the efflorescence that is caused by the underlying migration of moisture that travels through the grout joints.

      Also make sure you use an ASTM C920 sealant caulking recommended for submerged swimming pool applications at any tile transitions to mitigate the stresses they will be subjected to.

  3. Matt says:

    Pool with existing PTI TEC finish is 16 years and the Pebbletek liner is in good condition

    HOWEVER the Waterline tile is bad shape, I got told in order to remove/replace them I need to cut a line at the tile/Pebbletec junction before chisel the old tile off to prevent damage to the PTEC finish!?

    And then later after NEW tile is installed to grout that line between tile and PTEC with epoxy grout??
    1 what blade to use at the Ptek/ Tile junction
    2 what thinset for sheet porcelaine tile onto concrete/plaster wall
    3 which grout?
    4 why is epoxy more difficult to work?

    Thank you so much!!

    • Donato Pompo says:

      It is a good idea to first use a 4″ or 4.5″ diamond continuous dry blade on a grinder to cut out the joint. Use a vacuum shroud on the grinder to control the dust.

      After carefully removing the tile, the shotcrete or gunite concrete surface needs to be scarified and patched with mortar. If not too thick of an application you can use the thin-set mortar adhesive for patching

      Use a polymer modified thin-set mortar that meets at least ANSI A118.4 or A118.15 that is recommended for submerged applications. Laticrete, Mapei, Custom and others produce this type of thin-set.

      Most installations use a polymer modified cementitious grout. Some will use an epoxy grout that is more difficult to clean up if you don’t have the experience. In theory the epoxy grout is more stain resistant since there is no absorption, but it depends on how it is installed. If the epoxy grout surface is too textured it creates a maintenance problem.

      The transition joint should not be epoxy. It should be an ASTM C920 sealant suitable for submerged conditions such as the Laticrete Latasil silicone sealant.

  4. David says:

    I have a concrete basement floor that was covered in carpet and recently flooded. I removed the carpets andwas planning on putting down ceramic tile but understand that regular thin set may not survive submersion. Would it be reasonable to use a product that is used for swimming pools. If yes, what product would you recommend?


    • Donato Pompo says:

      Most thin-set dry set mortars for adhering tile are suitable for submerged applications and will last a long time. Just make sure that the data sheet for the thin-set mortar says it is suitable for pools, fountains, spas, and etc.

      You need to make sure that the flood wasn’t caused by water coming up from the concrete floor causing a hydrostatic condition that would affect the tile. If the water is coming from above the tile surface then it should be ok.

      If the concrete floor doesn’t have a vapor retarder under it to keep moisture from migrating up, it can cause efflorescence staining if there is moisture getting through.

  5. Jef says:

    I have a plaster finished pool and was looking to change it to tike. My question is can I use thinset right over the plaster after taking a wire brush and acid wash to it? And is it concerning to use a glass mosaic that is made for pools?

    • Donato Pompo says:

      Glass tile is often used in all tile swimming pools, but you need to make sure it is a quality glass tile for submerged pool applications.

      Whether you can bond your glass tile to an existing plaster finish pool depends on the condition of the plaster and what you do to prepare it.

      Plaster is typically about a 6:1 sand to cement mix which is on the weak side. Plus after being subjected to the pool chemicals for years it may or may not be a suitable substrate. If it is stable then you need to power wash it and make sure it will be a suitable surface to bond to.

      Plus if you are going to install a glass mosaic you need to shape the pool accordingly to accept the glass tiles and to install it in a professional way with an acceptable aesthetic appearance.

      Normally for all tile pools we float and shape the walls with mortar and preferably with a polymer modified mortar. We then waterproof the mortar bed with a liquid applied waterproof membrane. We then adhere the glass tile to the membrane with an ANSI A118.15 thinset mortar suitable for submerged applications. You do need to install movement joints with an ASTM C920 sealant suitable for swimming pool submerged applications at the coping to tile transition and at other transitions in the pool per TCNA EJ171.

  6. Ernest Horn says:

    Hello, my spa spills over into my pool. The spillway is travertine with fairly spall grout lines. over the years, the grout is eroding away and I want to re-grout it. What type of grout should i use. This is just for touch ups only.

    • Donato Pompo says:

      Chances are the grout joints to the travertine are too small so the grout can’t fully fill the joint as should be done. It is always recommended to go with a minimum 1/8″ wide joint, but never less than 1/16″ wide joint. You are never suppose to butt the tiles together as that can cause failures.

      Assuming that you have at least a 1/16″ wide grout joint you need to remove all of the existing grout and let it dry out. If necessary you can get a diamond dry cutting blade on a grinder and cut through the grout joint to remove the existing grout and open it up more. Then use a cementitious grout preferally sanded grout or a grout that is for both narrow and wider grout joints and fill it full and pack it in. Let the grout set up awhile before removing the excess and cleaning it up. Let it dry for at least 72 hours before you submerge it in water or as directed by the grout manufacturer.

    • Sana B. says:

      I have a fiberglass outdoor, I ground jacuzzi that I am having repainted with epoxy as I can’t get anyone to reglaze an outdoor jacuzzi. I’d like to tile the waterline after. What do you recommend as an adhesive?

      • Donato Pompo says:

        Keep in mind that if you are adhering a tile to an epoxy paint you should use an epoxy adhesive. Of course the bond strength of the tile will not be any better than the bond of the paint to the jacuzzi.

        Assuming the jacuzzi is fiberglass they normally use an ASTM C920 silicone sealant/adhesive to bond the tile. The silicone is resilient and bonds tenaciously so it can perform well over fiberglass. You might be able to bond the tile to the epoxy paint with the silicone depending on the characteristics of the paint. Epoxy adhesives do have some flexibility too and there are tile epoxy adhesives.

        You should test it out to make sure which works the best for you before doing the entire installation.

        • Walter Burstein says:

          Hi Donato,
          I have fiberglass spa, in the past tile has fallen off. This time I am in process of using silicone adhesive made for fiberglass spa. Is it a fatal mistake that I used Multi Surface Bonding primer painted onto fiberglass between it and tile ? I listened to the sales person who sold me mosaic tile . Thanks.

          • Donato Pompo says:

            Well on one hand the data sheet for Customs Multi Surface Bonding primer states that it can go over rigid fiberglass, but it also says it is meant to provide a surface for modified mortars and underlayments. It also says do not use where subject to prolong water immersion. So no you shouldn’t use it. 100% silicone recommended for fiberglass surfaces should be all you need as long as the fiberglass is properly prepared per the manufacturer’s directions.

  7. Joyce Wilson says:

    How do you properly prepare a new gunite pool for waterline tile and tile border on steps? Do we need to apply something such as a membrane directly on the gunite prior to applying the Thinset? If so, what product do you recommend?

    • Donato Pompo says:

      Depending on how they applied the gunite at the water line, you might need to grind smooth or fill in so you have a consistent flat and plumb surface. The finish surface should be porous.

      To help prevent effloresce staining, you can apply a liquid applied waterproof membrane that meets ANSI A118.10 such as Laticrete Hydro Ban. You should bond the tile with a modified thin-set mortar that is designed for submerged applications such as Laticrete 254 Platinum thin-set. Be sure to caulk the top and bottom joint of the tile as it transitions to a coping or to the plaster finish with an ASTM C920 sealant that is suitable for swimming pool applications such as Laticrete Latasil sealant. Normally you have to allow the tile 14 days or more curing before you submerge the tile.

  8. Herbert says:


    I had a pool retiled 16 months ago and am now losing multiple tiles mostly above the water line. Grout cracking everywhere. I’ve been told pool tiles should never fall off. Is this true? The builder has made multiple repairs but the problem persists. What course of action would you take?

    • Donato Pompo says:

      If the pool tiles were installed correctly they should not debond and the grout should not crack. If it is continuing then you might have a systemic failure, but the only way to know for sure if it is a systemic problem or if it is repairable is to determine what is causing the tiles to debond. To determine the cause will require experts like CTaSC to forensically remove tiles under various conditions in a very careful manner to look for evidence of deficiencies. Once you know the cause of the problem, then you can determine how to repair the affected tiles so the problem doesn’t reoccur.

  9. Linda Ayad says:

    I have a new concrete pool ready to tile. I am only tiling the water line and the feature wall and inside the spa as well as the spill way with mosaic tiles. I have had a cement renderer render the mentioned areas for tileing.
    Do we need to apply waterproofing prior to tiling or is the apoxy grout adequate to prevent calcium built up and to prevent other grout from deteriorating over time?

    • Donato Pompo says:

      You should waterproof all of the areas that will be tiled to keep the minerals in the concrete from absorbing in the water that later precipitates the calcium buildup as the water evaporates. I would use a liquid applied waterproof membrane for submerged tile installations. The joint below and and on top of the water line tile should be caulked respectively to the adjacent plaster and coping. The sealant needs to be an ASTM C920 sealant recommended for swimming pools.

      I would not put mosaics on the spa spill way as it is known to take a lot of abuse from the wet and dry cycles and have a tendency to build up calcium and have tiles debond. I always put a solid piece of dense granite or quartzite on it that works much better and doesn’t get the calcium buildup. Plus if gives you a nice level and straight edge for the water to uniformly cascade off the edge.

      Water spillways will always tend to develop calcium building because you have a high volume of water passing through with evaporation occurring in these areas that precipitates the minerals causing the calcium buildup. So that means there is more maintenance to keep it clean. It is relatively easy to clean when it first gets on the surface. If you wait too long it oxidizes and become insoluble and much more difficult to remove.

  10. Josh says:

    I would like your thoughts on a best practice to install porcelain tiles on a ICF constructed pool. I see a lot of water proof plaster being applied to ICF walls. Would it be best to apply a plaster base or use a membrane product such as Redgard to thin set the tile to? I would assume the plaster would give a stiffer base than a membrane base, but a porcelain tile in itself would increase stiffness with less leaching potential from the plaster. Would a more flexible thin set mitigate the risk of a straight membrane?

    • Donato Pompo says:

      Insulating Concrete Form (ICF) pools is not common. Obviously the EPS foam provides the benefits of insulation. I would treat it like we do on exterior veneers with insulation where we use stainless steel metal lath with tie wires anchored in the concrete. Then scratch and float it out with mortar to the intended shape relative to the type of tile used. Then apply a liquid applied waterproof membrane over the mortar and bond the tile directly to the appropriate waterproof membrane. Install movement joints at least at all transitions if not throughout per TCNA EJ171.

  11. Amy says:

    I would like to tile over a raised brick pool spa. It would only be the outside. The brick is uneven and old. I would like to use a mortar to even out the whole surface but am unsure which mortar to use. I am concerned about cement mortar because of cracking. What should I use to make an even surface?

    • Donato Pompo says:

      The tile installation can only be as structurally good as the original brick installation.

      Assuming the bring is structurally sound. You want to make sure it readily absorbs water and if necessary scarify the surface to remove any contaminates. Then power wash it to make sure there is no dirt or loose material. Then use a polymer modified mortar such as Laticrete 3701 Fortified mortar to bond over the brick to plumb the side and provide a smooth surface. I would waterproof it with a liquid applied waterproof membrane. Then I would bond the tile with a polymer modified thinset mortar that is suitable for the tile you will be installing. be sure to put a resilient movement joint at the top and bottom transitions following TCNA EJ171 Movement recommendations. Then grout the tile with an appropriate grout. Best to go with a single source manufacturer to ensure compatibility and best performance and to obtain a single source extended labor and material warranty.

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