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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Stephanie

This seems to be a floor site, but you are extremely knowledgeable, and I can not find the answer to my question anywhere! I am placing brick veneer on the wall behind a wood burning stove. Because of the contraction of temperature changes, I want to use a modified thinset. However, I am concerned that the added latex polymers will not handle the heat. I can also use type s mortar. They are just 1/2 inch veneers, but I don’t want them sliding down the wall as I put them up. What are your thoughts? The more I read, the more confused I get! Thanks!

Reply

Roger

Hi Stephanie,

The heat is not going to affect the polymers in powdered modified thinset at all.

Reply

Dusty

Hello Roger,
I’m installing wood plank porcelain on ditra. I’m using unmodified thinset like they recommend my problem is they say use large tile thinset and I can’t find any large tile unmodified thinset. What would your recommendations be on this?

Reply

Roger

Hi Dusty,

Regular unmodified thinset will work just fine.

Reply

Dusty

Awesome thanks for the quick response. Would u recommend a bigger notch than 1/4 x 1/4 which is what I normally use. I have always back buttered my tiles so was going to do that also.

Reply

Roger

I would use at least a 3/8″ trowel for that. 1/4″ isn’t nearly large enough.

Reply

Dusty

Thank u

Reply

Jake

Hey Roger, if any of your readers are in the Seattle area Master Wholesale sells the Bostik Ditra-Set for about $23! As well as may more of your top un-modified choices.

Jake

Reply

Roger

Thanks Jake!

Reply

Kara Brophy

Hello,
I am about to install kerdi around my hardibacker tub walls and the drywall guys mudded over the seams and the mud extends into the shower by about 5 inches. Should I sand it all off as best I can or will a latex or oil primer do the trick? I am using kerabond T for my thinset.

Also, would like to extend tile all the way to ceiling and am not 100% sure if that’s hardibacker all the way to ceiling. Tile shop told me ti use mastic above the shower head, but that’s contrary to everything I’ve read online.

Very grateful for your advice!

Reply

Roger

Hi Kara,

Sand it off as much as you can. If you can get to where you can see the seam you’ll be fine. As long as it’s above the shower head it doesn’t need to be hardi, but don’t use mastic (you already knew that). :D

Reply

Kara Brophy

Thank you so much for the quick response – much appreciated!
Is primer a good idea up top if I can’t sand off a lot of that? Bummer when you can’t trust the advice of the local reputable tile shop :/ That’s why I love your site!

Reply

Roger

Yes, primer will be fine if needed, but you don’t want to rely on that below the shower head. It is water-soluable, so when water gets to it it’s going to release from the wall. Anything attached to it will do the same.

Reply

Kara Brophy

Roger, Roger. Thanks so much!

Reply

Rich

Roger great info
I’m tiling over a concrete foot there was vinyl tile before,it was removed all that’s left is some glue . The vinyl floor is 60 yrs old . It’s probably asbestos glue that was used .there is very little glue left . Should I used Laticrete 317 with 333 additive ? If so should it be all additive mix or can I use half water ? Thanks

Reply

Roger

Hi Rich,

Yes you should. Just the admix, no water.

Reply

John M

Roger

I am a DIY working on replacing a tub with a walkin shower and am using the Schluter shower kit (base, curb, Kerdi membrane) plus a heated tile floor. I have unmodified thin-set mortar for applying the Kerdi membrane to the wall and shower base however was told by the retailer to use a polymer modified thin-set to bond the tiles to the wall and floor.

I am very confused (ok, easily accomplished) as your previous post about thin-set mortar types described the reasons for modifying the mortar was to increase curing time which in turn increases bonding strength. I am using 6 inch by 36 porcelain tiles so am concerned over binding strength. The confusion comes from the recommendation to use an unmodified thin-set mortar over the Schluter Ditra membrane…. does this compromise bonding strength ?

Also does this increase the curing time (the Schluter manual reads something like up to 60 days could be possible) and references latex leaching…. whatever that is.

Any guidance greatly appreciated !!

John

Reply

Roger

Hi John,

No, using unmodified mortar does not compromise bond strength. The fact that the membrane is waterproof and you are placing a large tile over it ensures that water in the mix does not prematurely dissipate and the full bond strength is reached. Using modified will increase cure time.

Everyone makes it confusing. Use unmodified to install your tile, you will have full bond strength as well as maintaining your schluter warranty.

Reply

John M

Roger

Thank you so much for fast response – I now know which type (unmodified) of mortar to use in the shower and need not be concerned over reduced bonding strength !

Should I use modified mortar for the floor tiles over the heating cable…. I am using the Schluter sheets with the raised honeycombs that hold the cable (sorry I cannot seem to find the correct product name) or would modified be a better choice for this area. I am using a 6 inch by 36 inch porcelain tile ?

Thanks again – your site is very helpful to DIYers !

John

Reply

Roger

If you are using ditra-heat then you need to use unmodified mortar to bond the tile to the mat over the wires.

Reply

John M

Roger

Thank you for the quick and informative reply.

I now understand which mortar to be using – unmodified over the Kerdi and Ditra-heat. The store that sold me the Schluter shower & floor heat kits, tile and mortar exchanged the modified mortar no problem. This time he recommended Laticrete 317 which after checking your site I accepted as I see you rate it quite highly. This is a bit a pain moving 50 pound bags of mortar to and from the site by snowmobile (on a seasonal road) but this is all part of the experience.

I have another question if I may impose….. I am installing 6 inch by 36 inch (3/8 inch thick) porcelain tiles on the floor and walls in the shower area and am wondering what size of trowel you would recommend. I was thinking of using a square notched 1/4 by 3/8 inch to apply the mortar to the wall & floor and buttering the tile with the Schluter Ditra trowel.(square notched 11/64 inch by 11/64 inch). Does this sound like it will work ok ?

Thanks,

John

Reply

Roger

Hi John,

Yes, those trowels will work just fine.

Reply

John M

Roger

Thanks – very much appreciate the quick and informative answers !!
I think I am now set up for a bit with your assistance.

All the Best,

John

Reply

Jason

Hi Roger,
I have Ditra heat TB mat and wire in, and now getting ready to put down large format tile (9″x43″ Porcelain tile). I have a bunch of laticrete 317 from setting the Ditra left over, but I wondered if TEC 338 uncoupling would be a better choice for the large format given it says it is suited for medium bed application. Thoughts?

Reply

Jason

Another quick thought is to use the 317 for a skim coat and fill the waffles and let it cure. Then come back with the TEC for the actual tile setting, mortar bed and back buttering…..

Reply

Roger

Hi Jason,

That would likely be the best option.

Reply

Jason

Thanks! I just wasn’t sure if I would run in to issues with 317 and TEC getting a good bond or not. Given they are both an unmodified, I wouldn’t expect an issue for adhesion between the two. Would you?

Reply

Roger

Absolutely none.

Reply

Dan

I appreciate the very helpful information you are providing and I’m scouring the Reno/Carson City area for the thinsets you recommend (with not much luck yet). I am confused however by a comment you made in your posting about modified thinsets–you said you always use modified thinset, even when Ditra calls for unmodified. Your comments on the unmodified thinsets in this article lead me to believe that you have considerable experience with them. I’m not particularly concerned by warranty issues–I just want to use the best product I can find–the last thing I want is a tile braking loose. Please clarify that for me–I confuse easily. Thanks, Dan

Reply

Roger

Hi Dan,

Schluter requires that non-modified mortar be used in order to retain the warranty. I have extensive experience with all sorts of thinset. I use what I want depending on the tile I am installing. Not too sure what your question is?

Reply

Clint

Aurora tile and marble
D&L tile

One of the two have ditra set can’t remember which

Reply

Steve

Too everyone that would like to get the ditra set it is available on amazon but very expensive. I did find it for 14.37 at a tile supply store so I feel very lucky.

Reply

Maureen

And Morris Tile carries Therabond. Beautiful to work with. No other tile stores in my area carry anything specific to decoupling membrane.

Reply

Maureen

Sorry. Kerabond!

Reply

Thom

Sorry, wrong email on my last question.
Can I put silica sand in unmodified thin set to make it unmodified medium bed?

Reply

Thom

I need to build up unmodified thin set over schluter to maybe 5/8″ but can,t find medium bed unmodified. Can I put silica sand in my unmodified thin set to make it not slump? Will this let me build up the unmodified to 5/8″ thick?
Sometimes these schluter products are irritating.

Reply

Roger

Hi Thom,

Why do you need to build it up that much??? I think it would be stable enough to be durable, but I’m not confident enough to tell you to go ahead and do it, it’ll be fine. KnowWhatIMean? :D If you tell me why you need to do that I can likely give you an alternative with which I would be confident.

Reply

shannon

My understanding (and we have done this on many occasions for installs) is that unmodified mortar is used for the lack of air between a plastic membrane of any sort (ditra or otherwise) and a porcelain tile. Please correct me if wrong.

Thank you,
Shannon

Reply

Roger

Hi Shannon,

That’s part of it. The biggest positive aspect of unmodified is that it will cure at a regular rate, like clockwork, whether it’s sandwiched between two impervious layers or not. Nearly everything will cure, eventually, but unmodified is reliably efficient with zero guesswork.

Reply

Joshua DeMarcinco

Hello and thanks for the specs and information….quick question..laid some mesh heated floor mats, skimmed them down with a modified thinset. We have several bags of unmodified ditra-set left over, would it be ok to use to set 18×18 tile over the cured modified or would you suggest sticky with a modified for the application?..thank you!

Reply

Roger

Hi Joshua,

I would STRONGLY suggest using a modified thinset for that application. You’re going to have a lot of expansion and contraction in that floor.

Reply

Mark

Will Tec 369 polymer modified mortar , full contact mortar work for putting Vitra down over plywood?
Will Tec 338 uncoupling membrane dry set white work for setting tile over Vitra ?
This is Menards offering. They no longer carry maipes products
Thankyou

Reply

Roger

Hi Mark,

Yes to both.

Reply

Maureen

I have Ditra down. I understand that I should not use self-leveling compound over it. But if I mix the unmodified thinset very thin and apply it over the Ditra, can I essentially get a self-leveling effect? I don’t know that I need extra help with leveling. But I’d like to have the reassurance that I’ve done all I can. Thanks!

Reply

Roger

Hi Maureen,

No you can not. You will get a self-leveling effect, but once it cures and all that water dissipates you’ll simply have an uneven mess. If you want an slc effect you need to use slc.

Reply

Maureen

Thanks. I have spot filled my low spots with kerabond over the ditra. I’m guessing it’s too late for SLC. I think I’m okay, though. It’s pretty good. I’m guessing that 12*24 tiles are too risky, all things considered. After all I’ve learned in the past two weeks of studying on the net, I wonder if any diy-er should tackle large format tiles as a first tiling project. BTW – When people talk about cracking, is this mostly in the grouting?

Reply

Roger

Yes, it is about the grout 95% of the time.

Reply

Marcelle

Can I trim my 6″ tall schluter shower curb down? is there a code on it?

Also, do I need to use unmodified thinset to attach my stone tiles to my Kerri membrain. What about porcelain?

Reply

Roger

Hi Marcelle,

Yes, you can trim it down to whatever you need. Most codes (check your local if you’re worried) require a minimum of two inches above your finished inside shower floor height. Schluter requires unmodified for ANY type of tile or stone over their products.

Reply

Ian

I am laying 1/4 hardibacker sub floor in my bathroom. Should I use unmodified or modified thinset? I will tape and screw, etc. thank you for you help. Love your website, blog etc. thanks. Ian.

Reply

Roger

Hi Ian,

Either one works just fine, it doesn’t need to actually bond to anything. It’s just there to fill space.

Reply

Maurice

Is kerabond T the same as straight kerabond ?
Thanks
Maurice

Reply

Roger

Hi Maurice,

No, kerabond t is a higher grade, non-sag medium bed mortar. It can be used anywhere you would use regular kerabond, though.

Reply

Mario

Roger –

I’m a DIYer and addicted to your site. Like, support group worthy.

I’m putting in a shower and will be tiling soon (used your site – AND PURCHASED ONE OF YOUR BOOKS! – for mortar bed, cement board, curb, etc). I’m looking around like crazy for Laticrete thinset and the only one I can find is Laticrete 253 Gold (a poymer modified thinset). I cannot find Laticrete 272 or 317.

Is Laticrete 253 acceptable for installing porcelain shower tile (4″ X 15 3/4″ subway tiles)? Also for 3″ wide glass mosiac running vertically along the corners?

Thanks in advance! Answer and I’ll buy you a bee…soda anytime you’re in Denver!

Mario

Reply

Roger

Hey Mario,

Yes, 253 is a very good thinset. The 272 and 317 are both unmodified, to be used over schluter products. The 253 is modified.

Reply

Mario

Wow! Thanks for writing back so fast! I owe you your favorite hop-flavored carbonated beverage.

I used a traditional waterproofing method with liner sandwiched between deck mud levels – all thanks to your website’s help.

As it turns out, I ended up with Laticrete 254 Platinum instead of Laticrete 253 Gold. Pricey stuff! But in the grand scheme, it’s only going to cost me $40 more for two bags and it says that it will be fine, even if submerged underwater. Now if my shower is submerged underwater in Denver, my guess is that I have bigger issues, namely whatever drove my dog to burst into flames and then fill the bathroom trying to put herself out …

Thank you again!

Reply

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