What is the best thinset?

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Old 02-16-09, 10:15 AM
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What is the best thinset?

I looking for opinions on what is the best brand and type thin set for this application. I want this to last so money is no object when coming to preperation. I'm using 1/4" Hardiboard over an OSB subfloor, then installing 12" porcelain tiles over that. Using Screws to hold down the hardiboard and fully secure the 2 layers of subfloor that equals 1 1/2".

Hardiboard instructions say to use a "mortar or modified thinset" under the board. What is the best here?? Laticrete, Tec, etc...and what type? For instance Laticrete has about 10 different "modified thinsets"; Mega bond, multipurpose, platnum, etc.. They also make an unmodified "floor adhesive" that would fall into the "mortar" catagory in the Hardibacker instructions. I know this is just to take up voids and not bonding so I'm not as concerned here as I am with the next thin set needed.

So, now I need a modified thinset meeting some ANSI code for bonding the porcelain tile to the hardiboard. What is the best here?? I see some Laticrete thinsets comply to this code but I can not find them at the local Lowes, etc. They have "Mega bond" with the latex additive but it does not say on the bag any ANSI code.

I'm looking to do this job once and not void any warrenty.

So, if anyone has done similar installations please let me know what you used and how it held up. Brand and type.

Thank you! Jim
 
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Old 02-16-09, 11:31 AM
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Hi Jim!

I understand you want a good installation, so we need to know a few more things before you begin:

What are the size of your floor joists (2x?), their center to center spacing, and the unsupported span of those joists.

It's important we find out that information so we can determine if your floor deflection meets specs.

Saying that, any portland based thinset will work for under the board. The thinset is not for bonding purposes, but just to fill any voids and have a solid footing for the board itself. I would personally use Versabond from HD, or a Megabond from Lowes. Both these meet the ANSI standards. I would used that for below and above the cement board.

A better product instead of cementboard is Schluter Ditra underlayment. It's a little more money, but takes less time to install.

In regards to warranty:

Install per manufacturers instructions. I know HD has a lifetime warranty if you use hteir cementboard, Flexbond thinset, and grout.

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Old 02-16-09, 07:46 PM
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Since you have to use a modified thinset meeting A118.4 or A118.11 when installing porcelain and also for any tile over Hardie, you may as well use the same under the board too. Hardie doesn't care which type goes under it, but it has to be modified to set all tiles.

Just a matter of which brand is easier to get. Both companies make various grades of each type. Unmodified thinsets meet A118.1 which I don't recommend you use.

VersaBond, although a decent basic mortar, is nothing to brag about. It's Custom's entry-level modified. (great for under Hardie though). Their Flexbond is much better. Laticrete,s MultiPurpose is modified, SpectraSet is better. Mega Bond is unmodified. Make sure you dampen Hardie just prior to spreading thinset. It will suck the life out of your thinset.

Jaz
 
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Old 02-17-09, 08:00 AM
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Originally Posted by HotinOKC View Post
Hi Jim!

What are the size of your floor joists (2x?), their center to center spacing, and the unsupported span of those joists.


Custom Building Products :: Do-It-Yourselfers :: Home

It's 16" on center, the house is only a few years old so it should be up to current codes.

The last installation was with Ditra and there was bonding problems so I'm staying away from it even though I'm sure it's good stuff when installed properly (long story). I spent 2 days tearing 2 grand worth of tile up, so I get mad when I see orange

With that said, I now have another question. The subfloor does have thinset residue on it that I scrapped off as best as I could with an ice scrapper. Do I need to spend 2 more days scraping all of it off or will the the new thinset take up some of the "texture" in the old thinset? Basically, how good does it need to be??

I talked to a Hardibacker rep and they also suggested Spectraset above and below the cementboard. They also mentioned that OSB is not a good subfloor because the water in the thinset can affect the bonding of the wood chips in osb and cause problems. They basically said it should be ok, but it's not the best. There is no way I'm going to tear up the subfloor...or add plywood to it.

Thanks for the info!
 
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Old 02-17-09, 11:45 AM
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Subfloor Size Question

What is the Min size OSB subfloor required for porcelain or ceramic tile? 3/4" with a 1/4" cement board? 5/8" with 1/2" CB Etc...

With 16" on center floor joists under it.
 
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Old 02-17-09, 02:16 PM
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5/8" usually, and the cement board has no structural value, so you don't count that for anything. I would rather use exterior grade plywood though.
 
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Old 02-17-09, 03:35 PM
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Jim

Sorry to here that you had a failure.

OSB will be fine under hardibacker. Thinset doesnt have to bond the hardi to the osb. Thinset fills any voids between the 2 layers and fully supports the hardi. The screws are what secures the hardi to the osb.

If you give us some details on what happened to your floor, we may be able to tell you why it happened, and how to avoid it happening again. I'm guessing from your original question that you used the wrong thinset to bed the ditra, yes.

The first layer of osb should be glued and fastened to the joists. The second layer of osb should be fastened to the first layer only. Stagger the seams so they dont line up with the sheets below. Use lots of screws here, every 8" in the field and every 6" a the edges.

Make sure you knock down any ridges left by the thinset. You should be able to install the hardi over what you have, provided you have gotten it pretty flat.

Use a good quality modified thinset to set your porcelain tile. Dont skimp on quality and buy the cheapo stuff. Jazman has made some good thinset recommendations. Tec Superflex is also a good choice and one that I use alot.

Have you checked to make sure that your joist structure will support a ceramic tile installation. If you tell us the joist size, unsupported span and species of the joists we can tell you if you are good to go. So far all you have told us about them is that they are 16" oc.
 
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Old 02-17-09, 03:39 PM
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Jim

It appears from your other thread that you have 1 1/4" of osb, 2 layers. Is that not the case?

Its best to keep all your questions in one thread so that we can help you without having to search around for info on your project.
 
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Old 02-17-09, 04:11 PM
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Threads merged.....................................
 
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Old 02-17-09, 06:24 PM
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Well, at least I learned a lot from that failure. Now I just need to find something to make out of 200 tiles with thinset ditra squares on the back of them. Maybe an outdoor bar. Beer 4U2

I started a new thread because that was a different project, I have 2 irons in the fire here. I always get in over my head.. I think you answered all my questions, thank you very much. The kitchen has 3/4 osb with a 1/2 osb glued over it. I'm ready to roll on that project with everyones advice.

My other thread was concerning a room that has 3/4" osb with only a 1/4" osb glued to it. I wanted to know what the min size is because I was thinking of pulling up the 1/4" due to some people saying you should never tile over any 1/4" material. This was before I found out it is totally glued down.. There is no way that is coming up. I would like to just add hardibacker and screw down though both sufloors. I can't imagine that 1/4" coming loose with a few hundred screws going through it.

Next time I build a house I'm making sure the subfloors are plywood....
 
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Old 02-17-09, 06:51 PM
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Originally Posted by HeresJohnny View Post
I'm guessing from your original question that you used the wrong thinset to bed the ditra, yes.
YES, good call. Used an unmodified thinset under the ditra Might as well used nothing because it didn't stick at all. I had some "I've done tile" guys install it, again long story... They never used Ditra and I was trying to save money by hiring "friends" so it's part/all my fault. Lesson learned, nothing worse than seeing grout cracking and crunchy tiles 2 days after an install. At least it made the tear-out go easy.

Someday down the road I will install ditra in a bathroom, correctly... I have a left over roll of it.

My Specs on the floor is as follows:
3/4" (osb) "Sturd-I-floor" exterior bond
1/2"osb over that, 1/4" in a different room.
12" Engineered (I beam) joists 16" on center
15 foot span

Thanks again for all your info, you guys helped me a lot with this.
 

Last edited by jimbremer; 02-17-09 at 07:06 PM.
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Old 02-18-09, 06:16 AM
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Jim

You are correct with the 1/4" osb underlayment being no good. There are no 1/4" sheets of anything (well except cement board, ditra lx, etc) that I'm aware of. If its glued and screwed well, you may be ok, but yeah, you are taking a chance with it.

Ijoists are typically speced to L480 so you are probably ok with what you have. You can check with the manufacturer to make sure. They typically publish span info on their websites and have technical people that can and will be happy to answer questions. 16" on center with 3/4" osb is good for all cement boards I'm aware of.
 
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