Unmodified Thinsets – A User’s Guide

by Roger

In my previous post about thinsets I explained what modified thinsets are and how they came about. That post actually started out as this post, I tend to get sidetracked by beer my dog.

Unmodified thinsets, in one form or another, have been around forever. With the expanded use of modified thinsets, the unmodified version had nearly gone by the wayside with everyone except us hard-headed setters who bought unmodified thinsets and added liquid admixes to them – to create modified thinsets. I no longer do this for my modified thinsets, but it was a hard habit to kick. :D

The reemergence (I know – doesn’t even look like a word) of unmodified thinsets came about in November of 2001. At an NTCA / Schluter workshop the statement was made that the preferred method of installation over ditra is the use of an unmodified thinset.

Mass confusion ensued.

This has continued to this day with even seasoned professionals questioning if unmodified should be used, and if so – why and which unmodified to use. This problem is compounded for do-it-yourselfers who don’t have nearly the understanding nor material and product access that we do. It’s difficult to find and purchase. If it helps, it’s sometimes difficult for us as well.

So let’s see if I can shed a little light on the subject and at least let you know which ones to look for and where. This list WILL be a bit biased. If you’ve read anything here you know I’m a Laticrete diehard. It is, and will continue to be, my preferred manufacturer for nearly every tile and stone setting material needed. That said typed, I do realize that other companies exist. :D

Just like modified thinsets, there are different levels or grades of unmodified thinsets. This is normally measured by the ratio or percentage of cement to sand in the mix. The higher the cement content, the better the thinset. More cement, more sticky, more stable.

It is also, in part, due to the type and percentage of whatever retention product is in the mix. For most thinsets (as far as I can tell – ancient guarded secret and all…) a powder called ‘hydrated lime’ is used. It is the same lime used by brick masons in order to retain water in the cement mix for a longer period of time, thus making the cured product stronger.

So that’s how unmodified thinsets are ‘grouped’ or graded – the ratio of those three items in the mix. Now that you know that, let’s group them in order according to how they are graded and perform. I’ll do this by manufacturer since most people only have one or two specific brands available.

Laticrete 317

Laticrete 317

Laticrete:

Laticrete 272 is considered the premium (best) – then Laticrete 317. There is negligible difference in these thinsets unless an admix is added to make them modified. For use as an unmodified I prefer the 317. Although they classify the 272 as their ‘premium’, they’re nearly identical.

The difference in these two thinsets: “There is more portland cement in LATICRETE 272 and the sand in the

Laticrete 272

Laticrete 272

LATICRETE 272 is slightly finer so it is a little bit creamier.” (Thanks to Anita at Laticrete for this clarification) The 272 contains 25-35% portland while the 317 contains 20-30% portland.

On the consumer side Laticrete products often have a different name – you may be familiar with Laticrete MegaBond. That is nearly identical to the 317. I use 317 for almost all of my unmodified thinset needs.

Mapei kerabond

Mapei kerabond

Mapei:

Kerabond: This is considered Mapei’s premium unmodified thinset. It works very well for any Schluter product

 

 

 

 

 

Mapei Keraset

Mapei Keraset

Keraset: This is Mapei’s mid-range unmodified. It’s not ideal but it works if it’s the only available. Give it extra time to fully cure! If you use Keraset be sure to wait a FULL 24 hours, at least, before the next step.

 

 

 

 

 

Mapei keraflor

Mapei keraflor

Keraflor: The ‘economy’ level unmodified from Mapei. I would not recommend using it for any shower applications or any regularly used flooring surface over ditra. Best to find one of the other two.

 

 

 

 

 

Custom Uncoupling Mat Mortar

Custom Uncoupling Mat Mortar

Custom:

Uncoupling Mat Mortar: This is Custom’s premium unmodified mortar made specifically for Custom’s spiderweb mat and other ditra-like products. It is difficult to find and has limited availability. If you can get your hands on it, use it.

Masterblend: Currently Custom’s only readily available (to my knowledge) unmodified thinset. It is available at most Home Depots. It’s a good sack of powder if you have a flood and need a makeshift levy. That’s it. Any reputable tile contractor will tell you not to use this for anything – ever. I’m one of them. The only really good thing I can say about it – It is an unmodified thinset.*

Custom masterblend

Custom masterblend

*This is by no means any type of intentional slander or slam against Custom building products! They make some great products. Masterblend, however, is not one of them in my opinion. And that’s all this is – my personal opinion. I do not consider this a viable product with which to install tile or stone over Schluter products.

 

 

Tec SturdiSet

Tec SturdiSet

Tec:

Sturdi-Set: Tec’s premium unmodified. A good unmodified thinset for nearly anything requiring one.

 

 

 

 

Tec full set plus

Tec full set plus

Full-Set Plus: Tec’s other unmodified. Comparable to a mid-range unmodified. It’ll work in a pinch if needed, but ensure full cure time before the next installation stage.

 

 

DitraSet

DitraSet

Bostik (Hydroment):

Ditra-Set: This is the best product with which to set anything over kerdi or ditra – it was specifically manufactured for that purpose. The availability is extremely limited, however. Most professionals don’t have ready access to it, let alone regular homeowners. So just plan on not finding this.

If you are lucky enough to find it you’ll feel ecstatic, like the luckiest person alive! If you don’t find it you’ll just think ‘Well, FloorElf told me I wouldn’t find it…’. See – win-win for me. Yay.

So in the groups above it breaks down like this:

Best:

Bostik Ditra-Set

Laticrete 317 (Laticrete MegaBond)

Laticrete 272

Mapei KeraBond

Tec Sturdi-Set

Custom Uncoupling Mat Mortar

Works if limited options exist:

Mapei KeraSet

Tec Full-Set Plus

It’s last call – find something:

Mapei KeraFlor

Go home alone and hold onto your wallet:

Custom Masterblend

So there you have it. The most commonly available unmodified thinsets and where they rate on the scale of quality. As I stated, this list is biased. The list above is the order in which I would use them if given the choice. Regardless of the order under each heading (Best, Works, etc.) this is how they are rated by their respective manufacturers.

Do not be surprised if you cannot find one of the quality products easily. They are not commonly stocked by regular big box stores except for the Laticrete Megabond. The best place to look for any of them would be at a tile supply shop. If, however, you are limited to normal big box stores, you can find some of the common products there.

Lowes will either stock Laticrete or Mapei. Home Depot will only (currently) carry Custom products. Menards normally stocks Mapei. Beyond those three, I have no idea what you may have around you.

You can always check the respective company’s website to find the nearest supplier. Since you will be looking for one of the more uncommon products keep in mind that just because you have a supplier near you does not mean you’ll find that particular product there. It’s always best to call the customer service line and ask them directly where you can buy the product you want.

One last thing – before anyone asks: adding more portland cement to a particular product may or may not make it better. Adding more cement to masterblend, for instance, will not make it comparable to kerabond. It doesn’t work like that. These thinsets, as all tile installation products, are put together in specific ratios in order to accomplish what the company wants. It may work, and it may not work. Unless you personally know someone in the chemistry department of the manufacturing plant there is no accurate way to tell.

ANSI Specifications

All thinsets, as well as any tile installation product, will have a specific ANSI (American National Standards Institute) number on the bag. This determines what type of product it is and what ANSI standard it meets. The number for unmodified thinset is A118.1. The ‘.1’ at the end determines the unmodified version. If you find a thinset you are curious about, and it is not on this list, look for that number. If it has A118.1 AND more numbers after that (with no mention of admix) then it is a MODIFIED thinset.

For instance, if it says on the bag that the product meets ANSI standards A118.1, A118.4 and A188.11 then it is a modified thinset. All modified thinsets meet the criteria set forth for unmodified thinsets as well, that’s why the A118.1 is on there.

ALSO! (I know it’s a pain, I live it) Most bags of UNmodified thinset have the A118.1 number as well as the A118.4, possibly A118.11 also  If it does it will plainly state that it only meets the last two standards (for modified) when mixed with the appropriate admix. Masterblend states that it meets all three – with the addition of admix (liquid latex). Don’t let this confuse you. They cannot legally misstate the ANSI numbers.

I hope this helps clear up a little bit of confusion about these products and helps you determine which would be appropriate or best for your project. As always, if you have any questions please don’t hesitate to ask them below. I answer them all. I’m just super cool like that. 8)

 

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lars

you said you no longer add an additive to the Laticrete 317, so what modified thin sets do you use?
What thin set should i use when installing kerdi backer board?
modified or unmodified?
i have a bag of Laticrete 317. its unmodified, right?
and when i install the porcelain tile i think i need to add an additive to make it modified, right? or can i use it as an Unmodified when installing the 12X12 porcelain floor tile
i plan on using a floor leveler, then a primer, thin-set, backer board, thin-set then the tile. sound about right? just not sure what thin-set to use where

Reply

Ralph

The hype that you can put ceramic tile down over correctly installed linoleum, true or false? Have a divot in the vinyl where fridge corner, uhh dug in when I pulled it out to clean. house is built on slab foundation. Can you give input on this? Enjoy reading your post.

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Mark

Is MAPEI Keraflor ok to use between 1/4″ HardieBacker and 3/4″ TG Plywood?

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AJ

II’m setting a shower floor over kerdi with natural stone mosaic. The tile is in light beige tones. Should I use the Grey Custom uncouppling unmodified mortor to set? I can not find Laticrete kerabond. Concerned with grey leeching into light colored stone? Alternatives? Tiles say to use latex modified?

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Roland

Hello Roger, I am installing ceramic tile 13 X 20 on drywall. Only the bottom half of the tub surround which will be two rows. What is the best thinset to use?

Thanks.

Roland

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Bill

Jason – read your post. I am in exactly the same position you indicate. I put up the Schluter membrane using Custom Masterblend unmodified thinset before I read this very informative post. The membrane is still on the wall a week later and it looks ok, but I was not comfortable that I got good adhesion while I was doing it. I haven’t tiled over it yet. Did you ever get an answer to your question – pull it down and start over? Is it still on the wall. Roger, what do you think? Thanks.

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Neil

Bill, per my earlier post, I was in your position. I decided to pull the membrane off the wall. There were parts that adhered solidly, but there were plenty of areas that were not. So pulling it down was the right move. Because the unmodified is already on the wall, I don’t want to redo the membrane, so I am going to smooth out the unmodified with modified, and use Redgard instead of the membrane. But I will still use the shower floor with Kerdi Band filling in the seams.

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Andy

Hey Awesome Roger (that should be your nickname, since it’s definitely true!).

I was an idiot :bonk: and didn’t read your mortar page until after I started using some Custom Masterblend. Thankfully I didn’t get very far with it, just did my kerdi-drain and a few kerdi-board screw patches. Allegedly Lumber Liquidators carries the good stuff, the Ditra-Set, so I’ll pick some up this weekend.

Anyway, I’ll pull off my screw patches and re-do them, but as for the drain I did, do you think I’ll survive? All I did was mortar it to the floor (wood OSB) with the curved punch-out wedgies from the Schluter shower tray, following Schluter’s video instructions.

Thanks a million! If I could pay you to read your site, I would, because the information here is truly that valuable! :rockon:

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Neil

Hi Roger,

I’m installing the Schluter shower kit. I used Customblend from HD, and put up the Kerdi membrane over cement backer board. I wasn’t comfortable that it adhered properly, so I pulled it down and plan to use Redgard instead. I was told to fill in the unmodified thinset gaps with modified thinset to smooth it out, and then apply the Redgard. Will the modified adhere with the unmodified already on the wall? And can I use a pre-mixed modified?

Thank you,
Neil

Reply

Bill F

Hi Roger,

Thanks for all the good information! And the humor! I’m setting 16×16 travertine tile on Schluter kerdi and ditra. Will Mapei uncoupling mortar be a suitable mortar to use for both the Schluter products and the tile? Subfloor is plywood, shower walls are sheetrock.

Thanks much,
Bill F

Reply

Roger

Hi Bill,

Yes, that will work just fine.

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Shaymouse

Hi Roger

Have you ever used Ardex, I’m UK based so can’t get Laticrete and was wondering if Ardex X78s (semi pourable) would be good for large format (28inch x 28inch) as an alternative to Mapei?

Interested to hear what you think – and thanks in advance.

Regards

Shaymouse

Reply

Roger

Hi Shaymouse,

I never have, but the guys who do absolutely love it. They have very good products, so yes, it would be a fine alternative.

On a side note: I have NO idea what ‘semi-pourable’ means???

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Jet

Oh boy i have question. Creating wet room. Outside shower area. Plywood subfloor, modified thinset, ditra, Unmodified thinset then tile. Good so far I hope. Now inside shower. Using a tuff form resessed pan with thier water proofing system then using kerdi membrane from walls to lay on the pan, waterproofing it on the pan with ARC waterproofing paint on stuff. How is that? the real issue is using tuff form and using kerdi for everything else. Tuff form has there waterproof stuff that you just role on, yet im so unsure about it. Any advice. Thanks.

Reply

jason

If you use tec 383 thinset to inbed the kerdi and wrap the whole arc pan and use kerdi fix around the drain you should be good. But if i were you i would just use the roll on waterproofing that comes with the kit.

Reply

Jsh

Will the Custom Uncoupling Mat Mortar work for adhering Kerdi to the sheetrock walls in a tub/Shower alcove? Can’t find any of the other recommended products.
Thank you!
jsh

Reply

Roger

Hi jsh,

Yes it will

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Wayne

Very frustrated:

I am preparing to lay 12″ x 24″ marble tile – that are almost 3/4″ thick – over Ditra-Heat. They are very heavy and I need to use a medium bed to help hold them up and level, but I can’t find an unmodified medium bed anywhere. Use Kerabond?

Reply

Roger

Hi Wayne,

You can use a modified over that.

Reply

Duriofont

Hi Roger,
HELP! I’m in the process of having Ditra installed and will be installing 8×32 porcelain tiles over the Ditra. The installation of the Ditra is almost complete. Although the flooring company used Custom’s uncoupling membrane thinset under the Ditra, they want to use Versabond to install the tiles in spite of my concerns about Ditra’s recommendations. They insist they’ve done this many times and it will be fine. According to the installer, the porcelain tile manufacturer recommends modified to install the tile. He did say he could find a modified with more sand if that would ease my concerns. Other than Schluter not recommending, what are the potential problems with his preferred method and why might he be hesitant to use unmodified? Please advise as to how I should proceed.

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Acacio

Hi Roger’
My steam room was not waterproofed properly when it was built. I’m considering rebuilding it, and I’m wandering if I can apply kerdi membrane over the existing tile to waterproof it and then new tile over it , or demolish the walls and start new.

Thanks in advance for your advise
Acacio

Reply

Bill

Regarding Custom Blend’s MasterBlend, I would agree with your assessment. I used this as the HD I was at only carried this product. The product did not work well and I would definitely not use this again. I have used Schluter’s Ditra and Kerdi numerous times before using either DitraSet or the UnCoupling Mat Mortar. Both of these products are very good and easy to use.

Reply

Birgit

HI. Not sue if you can answer this. I want to install a Kardi shower system and about to put on the water barrier. USg calls for unmodified Thin set Mortar but I only have the pre mixed Thin set mortar available. Does this still work?
The pre mix is composed of sand, calcium carbonate (not oxide) and some acrylic polymer…. (A136.1)

Thanks,

Reply

Roger

Hi Birgit,

Absolutely not. That is simply mastic with sand in it. You need to use powdered thinset sold in a bag.

Reply

Birgit

HI Roger

Thanks I am just about to start the project. I already bought the premix thin-set and wondering if it is OK to use for the ceramic tiles on wall and floor or better return it?

This is a really great site thanks for doing this,
Birgit

Reply

Roger

Better to return it.

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Bianca

Hi Roger!
Your site is very informative! I am preparing to remodel my bathroom and would like to know if I can use ditra shower pan with Kerdi waterproof membrane on the shower floor and then use Durock boards either Redgard on the shower walls. If yes, how do I seal the joint between the Durock and the shower pan. Thanks for your help!

Reply

Roger

Hi Bianca,

Yes you can. As long as you use a topical waterproofing on the walls also it’ll be fine. Silicone the backer to the pan, then paint the redgard down over it onto the pan.

Reply

Kyle

Roger

I want to install a porcelian tile over schluter on a covered concrete patio in southern california. The tile says that you must use latex modified thin-set but schluter says not to use modified thin-set because of the cure time that would be required. What do you suggest?

Thanks,
Kyle

Reply

Roger

Hi Kyle,

Unmodified thinset works just fine with porcelain over ditra.

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Tom

Just wanted say happy I found this post….dead on info. Before finding it, I used the cheap Mapei, as that was what I found at Lowes that said “unmodified”. I wet my backer board,which never really cured it’s thirst. The combo of those two made the application AGONIZING. I’d wager to say that you’re better off picking up after your dog and using that in place of the cheap floor thinset.

So found this post, and my time so had the Bostik Ditra set. Wow,that over the skimmed layer of cured thinset on the wall was night and day difference! Thanks for saving my project! !

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Jon Caswall

Trouble is, most floor tiles I lay nowadays are porcelain and laticrete recommend adding the latex admixture presumably making the adhesive modified, so not suitable for sutra matting…….. :?:

Reply

Roger

Hi Jon,

Yes, it will make it modified. What is ‘sutra matting’?

Reply

Apu

Roger
my contractor has used schluter product for waterproofing shower walls. the slab guy shows up and says I dont put slabs on this. After convincing he brings out Prospec b150 epoxy to put 2 cm slab on schluter. schluter does not recommend epoxy over their stuff. correct? what should I do?
please help! I have two days to stop this dispute between my contractor and the slab guy!
Thank you in advance!
-Apu

Reply

Roger

Hi Apu,

Epoxy is fine over Kerdi.

Reply

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