Difference between latex modified thin-set and polymer modified thin-set?


Modified Thin-set Cementitious Adhesives - Can you tell me the difference between latex modified thin-set and polymer modified thin-set?


ANSWER - There are modified thin-set adhesives that meet ANSI A118.4 or ANSI A118.15.  They can either me latex modified thin-set where you add the appropriate liquid latex rather than water or there are polymer modified thin-sets that have dry polymers in the powder and when you add water it activates them to give similar performance as the latex modified thin-set.

26 thoughts on “Difference between latex modified thin-set and polymer modified thin-set?

  1. Donato Pompo says:

    It isn’t that simple. First you need to know what kind of brick it is and whether it has any type of coating on it that you can see or not see. An easy test is to put water on it and see if it readily absorbs. If it does then generally it can be bonded to with a thin-set mortar. If it has a coating or doesn’t readily absorb water then you have to scarify the brick with some type of grinder.

    Once the brick is suitable for bonding to it, you should use a modified thin-set mortar that at least meets ANSI A118.4 requirements to skim boat the brick substrate. If the brick joints are deeper more than 1/4″ then you have to use a mortar that allows for a thicker application such as a Large and Heavy Thin-set mortar that can be applied as thick as 1/2″.

    Depending on the application you might have to float a mortar bed over the brick by first screwing in metal lath.

    After the brick substrate is properly prepared then depending on what type of tile you are installing you need to select the correct thin-set mortar. If it is a porcelain tile an ANSI A118.4 thin-set will normally work, but for glass tile and some other more difficult to adhere tiles you have to use a ANSI A118.15 improved thin-set mortar that will achieve better bond strength.

  2. Troy Carrington says:

    Unmodified or polymer modified thin set for large format (12′ x 24″) marble tile in shower wall application?

    • Donato Pompo says:

      Most thin-set manufacturers recommend either an ANSI A118.4 or A118.15 polymer modified thin-set mortar for porcelain tiles. Schluter is the exception. They use to only recommend ANSI A118.1 non-modified thin-set mortars when installing over their membrane, but now they produce a polymer modified thin-set so they might have changed their mind..

  3. Troy Carrington says:

    Thanks for the quick reply. They do make 3 new types (one of which is their All-Set, which is a modified). So given that, what I currently have meets A118.4 A118.11, which is the same as Schluter’s All-Set, the only difference is the brand (Custom)? Also, long story, but would that same polymer modified thin-set work over RedGuard?

    • Donato Pompo says:

      In theory, any polymer modified thin-set that meets ANSI A118.4 would bond to Custom Redgard membrane. Although it is always best to go with a single course manufacturer for installation products. So if you use Custom Redgard you should use their thin-set and grout. If you use different manufacturers for the different installation products and you have a problem then they all point fingers at each other. If you use all from the same manufacturer then you only have to deal with one company if there is a problem.

      • Troy Carrington says:

        Thanks again. I figured it would be that way, but as I said, long story. Had a contractor use both and do a really horrible job (he’s no longer on the job). So I’m left with what is here and going to finish it myself. Picture a patchwork quilt. Thanks for all your insight!

  4. MP says:

    Hi and many thanks for your expertise! What is the best thinset for 12×12″ porcelain tiles on a concrete, ground-level interior floor? There are slight cracks (about 1/16″ wide but going some length in the floor. The space gets a little vibration from a nearby train. Would you suggest anti-fracture liquid membrane such as RedGard as prep? I was thinking of using Flexbond Crack Prevention mortar (ANSI A118.5).

    • Donato Pompo says:

      Custom Bldg Products Flexbond Premium Crack Prevention Thinset mortar is an ANSI A118.15 adhesive, so it should bond well if you prepare the substrate properly and make sure it is clean and porous in that it will readily absorb water.

      The Flexbond thinset data sheet says “Protects against cracking caused by minor in-plane surface movement.” In-plane movement is shrinkage cracks that do not move vertically between each side of the crack. It only mitigates horizontal movement in shrinkage cracks.

      So based o their data sheets as long as your cracks are very minor, normally not more than 1/32″ wide, then you should not need to use the Red Gard crack isolation membrane. Although I would take the Flexbond thinset and using the flat side of the trowel skim coat over the cracks to fill them with the thinset. Then watch it for a week and see if it cracks through the thinset. It it does crack then you should also use a crack isolation membrane for in-plane cracks. If there is vertical displacement between the two sides of the crack then you have to make structural repairs.

  5. Barbara Duncan says:

    Hello Donato, I’m installing American Olean mosaic (linear) stone tile with a mesh backing as a backsplash in the kitchen. The directions say to use a white thin-set mortar with a flexible acrylic additive or a white polymer fortified thin-set mortar. This is my first attempt ar tiling. There are so many choices and brands and the recommended brand is mapei. Of course it is sold out. Could you recommend one? Also another question, the instructions say to use a 3/16 x 3/16” v notch trowel then knock down the trowel ridges with the flat edge. I don’t understand the purpose of the v notch then. Plus it says to back butter the sheet. But it doesn’t say how thin or thick to do that. The tiles are of multi size stones, some even have texture (linear grooves) some are smooth shiny marble. Instructions say to seal the tile sheet before grouting and again after grout. But I read that the sealer for stone is different than grout sealer. I’m really trying to understand all this before my attempt. Any answers/advice you can share would greatly help this mom-mom! Thank you

    • Donato Pompo says:

      There are a number of good polymer modified white thinset mortars. If the bag says it meets ANSI A118.4 then it is a good thinset. If it meets ANSI A118.15 they it is a higher performance thinset and more expensive. Each company has a good better best offering. Just make sure the bag says it is suitable for installing a natural stone. The main manufacturers are Custom Building Products, Laticrete, Mapei, TEC and others.

      The purpose of the trowel is to gauge how much thinset to apply to a surface. Depending on the angle you hold the trowel you can apply more or less thinset. On glass tile and some mosaics some installers will trowel the thinset creating notches and then flatten them out so there are not voids and to try to avoid the thinset getting into the grout joints, which you then have to clean out before it dries and becomes too hard to remove.

      It is recommended to first apply the thinset with the flat side of the trowel forcibly against the substrate leaving a slight skim coat of thinset and do the same to the back of the tile to ensure a good bond. Then use the notch side of the trowel to apply and gauge the amount of thinset, so it is enough to make full contact between the tile and its substrate, but not too much where it fills too much of the grout joint causing you to have to clean it out before it fully cures. Then forcibly beat in the tile and shift it to fill all voids. Pull tiles occasionally right after you set them to make sure you are achieving full thinset contact.

      On large tiles you are suppose to trowel in one direction so that the ridges of the thinset are parallel to each other. Then you embed the tile forcibly and shift it perpendicular to the thinset ridges so the ridges collapse into the valleys in order to try to achieve 100% thinset contact between the back of the tile and its substrate. This method prevents air from being trapped under the tile.

      Regarding using a sealer before you install the tile they do that to prevent potential staining of the tile by the thinset or by the grout. You have to be careful whey you apply the sealer to the face of the tile to not get it on the edges as the sealer can act as a bond breaker.

    • Donato Pompo says:

      Mapei has several thinset mortars that are polymer-enriched. It is likely that any of those mortars can be used to fill the USG Durock cementitious backer board in a shower embed with alkali-resistant, fiberglass mesh joint tape. Whatever thinset you purchase, just verify on the bag that it is suitable for interior wet areas.

  6. Stacy says:

    We’re planning to install porcelain plank flooring OVER existing 19″ square porcelain tiles. What is the best thinset to use for installing tile over tile?

    • Donato Pompo says:

      The tile installation will only be as good as the existing installation so make sure it is structurally sound.

      I would scarify/grind the existing tile surface first and clean it. Then I would use an ANSI A118.15 improved modified thin-set mortar that has much higher bond strength. All of the major manufactures such as Mapei, Laticrete, Custom Building Products all of these types of thinset mortars. Make sure the instructions show that it is suitable for bonding to existing tile.

  7. Bret says:

    I appreciate your posts here. I have another Redgard question. Does Versabond LFT mortar work as well as Flexbond mortar over Redgard? I’m using 18” tile which needs the larger format recommendation, I just want to make sure it will work in Redgard.

    • Donato Pompo says:

      Custom Building Product’s data sheets for the two products indicate that either one can be used over Redgard waterproof/crack isolation membrane. Red the product’s data sheet and it says Redgard is a suitable substrate for each of them.

      Versabond LFT is an ANSI A118.4HT thinset. H means for heavy tiles and T means it is sag resistant. Flexbond is an ANSI A118.15 thinset meaning it has greater bond strength and it is a crack resistant and is suitable for glass tile.

      Using the Versabond LFT with the 18×18 tile will make it easier to avoid tile lippage. Its bond strength is good enough for a porcelain tile. Flexbond is more flexible and will provide some crack isolation protection, but you are already using Redgard that should do that.

  8. Ruth D says:

    I am detailing a ceramic tile (size t.b.d. but it won’t be larger than 6-8″) shower floor and walls, in a bathroom that will be tiled with the same tile. The bathroom is in an existing, 100+ year old wood joist brownstone. Walls will be new. Subfloors will be marine grade 3/4″ plywood. Currently thinking that all walls will be thin set with latex mortar and the floor, shower floor and shower curb will be mudset. Do you agree, or recommend epoxy thinset, at least for the shower walls? Thanks for your expertise!

    • Donato Pompo says:

      What is most important is how the walls will be constructed and with what materials. Industry standards state that the walls cannot have more deflection than L/360, which isn’t much. The walls need to have a vapor barrier and be waterproof over a substrate that isn’t moisture sensitive. The wood subfloor needs to be presloped and waterproofed and tied into a two part drain with weep holes or to a trench drain. It is good to mudset (mortar bed) the shower pan and curb. We always recommend a primary waterproof membrane under the mortar bed over a pre-sloped surface, and a secondary waterproof membrane over the top of the mortar bed to keep water our of the mortar bed and to have crack isolation protection. We do offer a free Tile and Stone Installation Guidelines download on our website at https://ctasc.com/expert-answers-overview/ that you should read.

      Most installers don’t know the industry standards and unintentionally can cause conditions that can cause problems, so make sure they follow industry standards.

  9. Andy says:

    We are installing a paper faced glass mosaic tile on out fiberglass pool. What is the the proper thinset or tile adhesive? It is my understanding that it has to be white so the color will be correct.

    • Donato Pompo says:

      To install glass tile on a fiberglass surface you will have to use an epoxy adhesive or sometimes they will use a silicone sealant. You need to check with the manufacturer of the adhesive you use.

      Normally for thinset mortars they use a white ANSI A118.15 improved modified thin-set mortar. If the tile is translucent without a white backing then it is important to get full adhesive contact with our any trowel ridges or otherwise you might see them through the glass tile.

      Paper faced glass mosaics is the the test to use so you can get 100% adhesive contact to it and in the grout joints. Web backing on glass tile sheets can be problematic if the glue used is water sensitive or not compatible with the adhesive.

  10. Shelly says:

    Hello! We are looking to install a marble tile around a fireplace. We have removed the existing tile and found they tiled over the metal fire surround. The manufacturer says any materials used on the metal surround must be non combustible.
    Are there specific thinsets and grouts that can be used on this metal surround or should we plan on trying to clean up the metal surround and just tile the drywall around the metal?

    • Donato Pompo says:

      To bond to metal, you have to scarify the surface of the metal and use an epoxy adhesive.

      There are epoxy adhesives that meet ANSI A118.3 and ANSI A118.5 that is even more resistant to heat and chemicals. There are modified epoxy adhesives that combine a cementitious material with the epoxy such as Laticrete Latapoxy 210. Non of them should be combustible.

      A fire surround normally doesn’t get that hot, but look at the epoxy adhesive data sheet to determine which will be best for your situation.

  11. Vernon Bush says:

    Hello. I’m sure you’ve seen some of the confusion regarding Schluter’s All-Set mortar which is a modified mortar, but Schluter’s advises not to use modified mortar with Kerdi-board but does advise its OK to use AL-Set with Kerdi-board. This opens up the question can you actually use modified mortar on Kerd-board, especially mortars with Latex additive? If using a modified mortar on kerdi-board with latex additive how much longer would one be expected to wait for full curing. I assume that curing would be slower with square tile where curing would have to be via grout lines but would be quicker with, say sliced stone, which would be much more open. Is this assumption correct?

    Thank you, Rgds Vernon

    • Donato Pompo says:

      Keep in mind that tile installation product manufacturers want you to only use their products to maximize their profits and to help ensure compatibility and single source responsibilities.

      Schluter originally pushed non-modified thin-set mortars saying that with impervious porcelain tiles that the thinset would set up faster than polymer or latex modified thin-set mortars. Then they came up with a modified thin-set mortars. So if you are installing Schluter products then you should follow their directions to ensure the maximum warranty.

      The reality is that polymer modified or latex modified thin-set mortars are mostly used today for installing porcelain and other types of tiles. Often these impervious porcelain tiles are installed over an impervious membrane so there is very little drying through absorption. The polymer modified thin-sets are formulated with water retention chemicals and accelerators so that the thin-set mortars cure at a reasonable rate through a hydration chemical process. Most polymer modified thin-set mortars want the thin-set to cure 24 hours before grouting and at least 72 hours before being subjected to high traffic conditions. There are also rapid setting thin-set mortars that indicate the tile will be ready for grouting within 2-4 hours.

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