Modified Thinset – A Brief History

by Roger

Laticrete 3701What is the difference between modified and unmodified thinsets?

Which unmodified thinset is better?

What makes a modified thinset modified?

Why do you drink so much beer?

These are questions I get asked a lot, along with ‘why is my dog on fire’ (because you used the incorrect product for a specific installation).

Unmodified thinset is simply a thinset which does not have any latex polymers or other products added to it. It is essentially portland cement, silica (sand) and lime. Recipes vary, but those are the basics.

History (pay attention – there may be a quiz…)

To understand modified and unmodified you should understand why modified exists. Way back in the 1940′s Henry M. Rothberg was a chemical engineer. Back then the standard installation procedure for floor tile was the full bed method. This was a 2″-3″ deck of portland cement and sand upon which tile was installed. The need for the thickness is at the heart of the development of modified thinsets.

It needed to be that thick in order to retain enough moisture for the cement to fully cure.

Concrete cures through a process called hydration. The cement chemically reacts with water and grows interlocking crystals – these interlocking crystals are what gives cement it’s hardness. These crystals grow as long as they are exposed to moisture (water). Once the water is gone the crystals slow and stop. So…

The longer the cement is exposed to moisture the longer the crystals grow. The longer the crystals grow the more they interlock. The more they interlock the stronger the concrete.

It’s all about moisture retention in the mix. Enter Latex (or rubber). Rubber was added to concrete mixes in the early 20′s to repair and solidify sea walls, and later added to brick mason’s mortar to make brick installations stronger. Adding rubber or latex to cement mixes helped the mix retain water for longer periods of time.

Mr. Rothberg realized that the common tile installation methods at the time had limitations. He set out to find a way to solve this. He began experimenting with the natural latex which was being used in sea walls and brick work but soon realized the these products had limited working time and were difficult to store for any amount of time before degrading.

He then set out to develop a synthetic form of latex which would be easily stored for longer periods and had an extended working time in order to be feasible for tile installation purposes. After developing and testing more than 300 different chemical compositions of synthetic latex rubber he finally found one that met his criteria.

It was introduced to the market as ‘Laticrete’. It was a liquid latex polymer which was added to concrete mixes to make them stronger and give them some flexibility.

That’s right, my favorite company actually has a story. :D The name is a pseudo-compound word formed from ‘latex’ and ‘concrete’. This was the name of the synthetic polymer Mr. Rothberg created for use in tile installation products in order to retain moisture in the mix and allow it to cure stronger and not be as brittle.

In the 1960′s the (then) Tile Council of America developed a powdered thinset with dry polymers which were activated by adding water. Soon afterward it was used by nearly everybody for nearly every installation. This actually led to a lot of problems, mainly due to misunderstanding of the product and it’s limitations – it was being used for everything with unrealistic expectations.

The latest modified thinsets have come a long way from the original TCA types and are now tested to minimum standards in an attempt to keep expectations realistic. Powdered or liquid polymers added to regular thinsets help the mix retain water for a more durable end result, as well as adding flexibility, bonding power, or any number of specialty capabilities needed for the numerous installation requirements.

Any thinset that has either a powdered or liquid latex polymer added to it is considered a modified thinset. Any thinset that does not contain these is an unmodified thinset.

This post began as a description and information on unmodified thinsets and which are better. I realized very quickly that this was not a subject that can be easily explained in one blog post. It can – but you’d get bored. So my next post will deal with that topic now that you know why modified thinsets exist and what they do.

 

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Michael

- I’ve used the Laticrete Hydroban over the Hardiebacker. Great color!
Can I use Mapie Ultraflex 2 over the Hydroban?

Reply

Roger

Hi Michael,

Yes.

Reply

BC

Long story short, we were given some bad advice and porcelain tile was installed on the shower floor using MAPEI Powder Dry-Thinset Mortar with only water added, no polymer mixed in (Lowes Item #: 12795 | Model #: 12250136, Exceeds ANSI A118.1 bond strength requirements when mixed with water;). Yes, I know the bag clearly says for Porcelain tile, you must mix in a Polymer. Don’t ask, stupidity seems to permeate every home renovation project we tackle regardless of how hard we try.

We applied redguard over the mortar shower bed and let it cure a day before the contractor installed the porcelain mosaic tile (yes, i know the contractor should have known better too). The tile job is done. It is a guest bathroom and the shower will be used very infrequently. Is this just a total disaster waiting to happen? Is there any chance it holds up? Is there anything we can do at this point?

PS – same mistake on the rest of the bathroom floor with large 12X24″ porcelain tile. Redguard was also applied for crack preventtion.

Reply

Roger

Hi BC,

It’s fine. It’s just unmodified thinset. While modified is better, unmodified will work just fine.

Reply

Kevin

Roger,

I think I saw this info somewhere on your site, but couldn’t dredge it up this time- What is the final thickness of the thin-set under tile once set for different notch sizes? I know it will depend, but on average for deck height estimating.
1/4 x 3/8; 1/2 x 1/2

Thanks,
Kev

Reply

Roger

Hi Kevin,

A 1/4×3/8″ will give you about a 3/16″ layer, and a 1/2″ x 1/2″ will give you a 1/4″ layer. The minimum layer thickness beneath your tile is 3/32″, so either will work just fine.

Reply

Dale

Hey Roger – Apologize for having to ask but couldn’t find anything already on your site. I’m building a bar top. It’s relatively small, only about 12 sqft. I’m planning to use Granite Squares, either 12″X12″ or a 12″X12″ mosaic (2″X2″ squares). Can you recommend an adhesive?

I know you’re a Laticrete aficionado , which based on your previous advice I found to work very well on previous projects. Not sure what works best with Granite, though. And the lazy side of me wondering if there might be a premixed product that would be available? I’m not expecting this to be a wet area, unless someone spills their Martini.

Thoughts?
Thanks,
Dale

Reply

Roger

Hi Dale,

Laticrete 253 is my preferred thinset for granite. 4xlt is also very good. You never want to use premixed with natural stone, the oils can absorb into the stone and discolor it.

Reply

Charley

I got my pre-slope shower base in – now waiting for it to cure for the recommended 3 days before putting on RedGard – and I am preparing for the wall tiles of the shower – I bought a bag of Flexbond from Home Depot and wanted to double check if this is ok before moving forward or should I go out and get Ultra Flex 2?

Thanks
Charley

Reply

Roger

Hi Charley,

The flexbond is just fine. It’s a good thinset.

Reply

Elfriede

A water pipe leak in my bathroom required the removal of tiles, drywall and studs. The restoration company which did the rebuilding, put greenboard over the wall studs, with no moisture barrier behind it. They used drywall mud and regular drywall tape over seems. No mud over the drywall screws. According to them it is now ready for the tiles to go over it. When I commented that I had read about the need for some kind of waterproof barrier to be put behind the tiles, I was told to trust them, as they always do it this way (no moisture barrier) and they have never had a problem. I am worried about moisture problems in the future (especially around the bathtub) I would be grateful for your opinion, so I have something to back up my argument when I talk with them next.

Reply

Roger

“Trust us, we’ve done it hundreds of times and never had a problem”. This is my reply. TCA standards (EVERY ONE OF THEM) require a MINIMUM of a moisture barrier behind a water-stable (greenboard IS NOT) substrate. Greenboard is no longer approved, and hasn’t been for at least six years now, for use in a wet application. A shower is a wet application.

If they build you a shower and you have a major problem with it – water damage, mold, etc. – would you call them to come repair it? I wouldn’t either – that’s why they think they’ve never had a problem with it. What they are doing is not correct shower construction. It just isn’t.

Reply

cory

i was looking for a video that explained the crystalization process and maybe even showed a dramatization of Henry M. Rothberg ideas.

Reply

Roger

Hi Cory,

None exist of which I am aware. You can find Henry on facebook – ask him. He WILL answer you and point you in the right direction to at least get you more information about it. You can find him here: Henry Rothberg.

Reply

Betsy

Roger, thanks so much for this site, but even after reading and reading I’m still not sure what to do. I have a 4ft x 8ft shower that is ready for tile. It was built by a contractor with Durarock then waterproofed with Red Gard. I’m planning to put 24×24″ ceramic tiles – very thick – maybe a half inch? on the walls. Smaller 2×2 tiles on the floor. Here are my questions: 1) Use modified or unmodified thinset? I’ve seen both recommended with the waterproofed Red Gard by different people…I’m very confused.
2) Lay the floor or walls first?
3) Any other tips for these super heavy wall tiles? Like grout size, back buttering, trowel size, etc.
It just seems that the more I read, the more confused I get. Thank you so very much for your help.

Reply

Roger

Hi Betsy,

1. Use modified thinset over redgard
2. Either works fine. I prefer the floors first.
3. Grout size depends on your tile and how consistent it is, it’s a personal choice. Always backbutter, especially large format tile such as that. Trowel sizes: Which trowel to use

Reply

GEM

roger, how to pick the right thinset I see the prices vary at the box stores but I don’t want to pick on price I just want the right one for the application and then choose on the price :-D . I am doing a bathroom and shower in the shower I used aqua defense and am wondering if I should us the same thinset for everything… floor, walls, inside shower outside?? I can give you specifics as to brands and kinds carried at the local stores but I am just wondering what to look for?

Reply

Roger

A good modified thinset will work for all of it. I prefer laticrete 253 as my go to thinset.

Reply

GEM

How to know a good one….? I didn’t mention that I am using Porcelain tile so I don’t know if that makes a difference or not? The blue store changed to Mapei in our area from Laticrete and they have one for ceramic and one for porcelain at $11 more per bag for the porcelain is there really a difference? I don’t want to screw it up by being cheap but that can pay for the beer :-D :!:

Reply

Roger

Mapei ultraflex 2. Don’t know which specific products you’re speaking of so I really can’t say how much different they may be. :D

Reply

GEM

Roger, so what size trowel would you recommend for 18×18 Porcelain. Square notch? V notch? I am being told 1/2×1/2 square and that looks huge. I appreciate all you time and help!!

Reply

Roger

3/8″ – 1/2″ square notch. I prefer the 3/8″ as long as you get the coverage you need.

Reply

Alexander

Roger, sorry, but I got confused. So much information – but I still don’t understand which exactly thinset to use for floor tiles over the hardiebacker? Modified? Unmodified? If unmodified – what to add?

Thank you for your wonderful posts – I spent today all day reading them!

Alexander

Reply

Roger

Hi Alexander,

Regular modified thinset. Don’t add anything except water to it.

Reply

Short on time

Please ignore phone number that accidently got pasted in my previous question. If you could delete it that would be great, I think the guy whose number that is would be pissed to see it published on a blog. Thanks!

Reply

Roger

Man was that guy pissed when I called him. :D

If you read through Creating a shower floor for tile it describes the entire process. The liner is not bonded to the pre-slope. Thinset will not stick to the liner – you need two mud decks. One beneath the liner and one over it.

Reply

Ally

I am renovating my bathroom and would like to tile my tub surround up to and on the ceiling. I will be installing the Kerdi system for waterproofing as I have drywall. We had the plastic stick up tub surround but the moisture was getting in the ceiling and creating mold so I don’t want to put that back up. My question is do you have to remove all the glue from that or can we put the thin set and Kerdi over it? Also along the bathtub the lip against the wall is back further than the drywall do you just fill that with thin set and set your tile down to the bathtub ledge?

Reply

Roger

Hi Ally,

You need to remove as much of it as you possibly can. You don’t know how well the thinset will bond to it long-term. Is it worth the risk? I don’t believe it is. As long as you can get it to where it’s just a ‘stain’ of the glue rather than actual rubbery glue on there it should be fine.

Reply

Keith

Hey Roger, long story short i have a bathroom floor in which i installed ditra mat (orange waffle mat stuff). stuck it down with premix thinset i know thats the first wrong. then i set the 12×12 tiles to it with some more premix thinset, i know second wrong. So now i am in the process of poping those still wet (its been 3 weeks) tiles back up off of the mat. my question is…if i scrape the premix crap off the back of the tiles and get most of that stuff off of the mat can turn around and use the correct morter to set them back down and be good to go? and will the residue and little bit of premix left on the tiles and mat compromise the setting with the new morter? I am 99 percent positive that the premix used to set the mat down with is set up fine.

thanks

Reply

Roger

Hey Keith,

Unfortunately you’ll likely need to replace the ditra. I don’t know that you’ll be able to get enough of the premixed out of there to enable the thinset to mechanically bond the tile to it properly. You should be able to reuse the tile if you get the mastic off of them, though.

Reply

Craig

not to be a know it all, because I know practically nothing, but I think you maybee could save the ditra……if you pull up the tiles and scrape the excess premix off the ditra and then let the residual premix dry (which it should with no tiles on top, right?), then use the proper unmodified to set the tiles, I would think that the unmodified would bond to the premix that may be left in the waffle dovetails, thus giving you the mechanical bond. If the unmodified won’t bond to the premix then you are screwed. Roger???? I am not a plumber nor a tile guy, and I don’t even play one on TV.

Reply

Roger

Hey Craig,

Cured mastic (the premixed ‘thinset’) is not porous at all. Thinset will not bond to it, there are no open pores into which the cement crystals can grow. If it did bond to the mastic you’d be correct, but it won’t. Attempting to remove the mastic from the dovetails will do more to destroy the ditra than it would ridding it of the premix.

Reply

Keith

Thats just it though, the premix thinset after it dryed still did not bond to the ditra. it actually just vacuumed right out of the waffle squares in little square chunks.

Reply

Craig

Keith:
That is by design; I don’t think any thinset will “stick” to the ditra (I think that is why they have the mesh on the underside as the thinset can stick to that). And that is really the point of the ditra, it isolates the tile from the substrate which is subject to movement. The tile and thinset is more locked to the ditra than it is bonded or stuck. It is locked via the waffles.
I sure hope you don’t have to pull the ditra as I cant imagine there is an easy way to do that. I just completed my first ever tile work and I used ditra and followed all Rogers’ tips and it has come out pretty good. Good Luck!!

Reply

Roger

Well if it came out without damaging the ditra then you can still use it. I DO NOT like the mastic under the ditra, but it isn’t my floor, eh? :D

Reply

Nancy

Would like to install subway tile above newly installed tub so ill be tiling three sides. What is the best way to start-right on tub and level first row?

Reply

Roger

Hi Nancy,

That’s normally how I do it. You can also use a ledger board starting one tile height from the lowest part of the tub (if it isn’t level).

Reply

Karl

What is your recommendation for modified/unmodified thinset with glass tile 1″ x 1″ to be installed in a shower niche on top of kerdi. The kerdi manufacturer does not appear to want any modified thinset due to drying time, but the glass needs modified. Will using a modified thinset (I currently have laticrete 253 gold that I was planning to use) with the small glass tiles work on the kerdi? Should be able to dry in a reasonable time with so many grout spaces or not? In your experience what have you done or would recommend?

Reply

Roger

Hey Karl,

I’d just use the 253. It works just fine with the glass. You’ll lose your warranty, but it’ll work.

Reply

Steve Sass

Do you have a recommendation on modified thinsets like the piece you did on unmodified?

I am looking to put a scratch coat on 3 different areas that I will be installing heat mat.

Area 1. bathroom floor over a sandwich (3/4 120 year old subfloor, 1/4 plywood, planipatch, 1/4 playwood). I will install Ditra over all of that then 9×18 stone tile
Area 2. bathroom floor over new 3/4″ OSB TG. I will install Ditra over that as well
Area 3. Front door, this one complicated. Concrete for 1/3 of the area which I will cover with warmup insulated backer, sandwich similar to Area 1. I will get all of these to the same height, then install the heat, Ditra and 18×18 stone tile with a soft joint at the location of the wood concrete interface.

What should I use for a scratch coat. I have access to Mapei products.

I will also be installing some porcelain/ceramic shower tile that I topical waterproofed per your manual. What modified whould you recommend for that.

Reply

Roger

Hey Steve,

Ultraflex 2 would be fine for everything you’re doing. Ultraflex 3 would be better for the floors, if you have access to that.

Reply

Joe

What do you recommend for tiling over cutback

Reply

Roger

Hey Joe,

Not tiling over cutback. :D

I always mechanically scarify the surface to remove cutback until the floor will soak in water when splashed on it (that indicates that thinset will bond to it). There are thinsets that are approved for use over cutback, I believe mapei ultraflex 3 is one such thinset, but you’d need to check with mapei to make sure.

Reply

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