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recommendation for unmodified thinset between hardi and wood subfloor

recommendation for unmodified thinset between hardi and wood subfloor


  #1  
Old 03-13-12, 07:59 PM
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Question recommendation for unmodified thinset between hardi and wood subfloor

I just finished ripping up 100sqft of floor tile and the 1/4" wood underlayment, now it's time to make it nice again.

Planned setup:

* 3/4" wood subfloor, in good condition
* 1/4" hardibacker (1/4" square notched for thinset)
* 6" and 12" porcelain tiles (3/8" square notched for thinset)
* Laticrete 1500 sanded grout (with their liquid admix)
* Laticrete MultipurposePro modified thinset (for tiles)

I've read many discussions (on here and elsewhere) on modified vs unmodified thinset for between hardiboard and subfloor. Hardi recommends either, they just want you to have one. I believe unmodified will work better because I agree that it fills any voids you may have without bonding the two surfaces.

Three questions:

1) Recommendation on unmodified thinset (brand and type. I currently have Laticrete Floor Adhesive, basic unmodified but have never seen it discussed... don't know much about it)

2) Recommendation on grout sealer. Leaning towards DuPont's StoneTech grout sealer.

3) Preventing grout haze. I've seen many people disappointed that they can't remove it. Seems like cleaning up with a damp sponge (constantly rinsing it in clean water) right after grouting can prevent this, any other tricks?


Thanks for you insight!
 
  #2  
Old 03-15-12, 07:30 AM
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I read more on the 'Flooring Adhesive' from Laticrete, it seems to really just be a basic unmodified thinset.

Would there be any benefit in returning it for the MegaBond from Laticrete (a slightly more expensive unmodified thinset, usually mixed with a latex additive). Wondering if anyone knows of a quality difference that may hold up better?

Or any specific brand and name of an unmodified thinset for between hardi and plywood subfloor you've had success with in the past?
 
  #3  
Old 03-15-12, 05:50 PM
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Hi skibum,

You can use any thin set to install your Hardie. It makes no difference. Just switch back to a decent modified for the seams and to set the tiles.

If it were me I would just buy 2 bags of modified and use it for both operations. Otherwise you'll need a total of 3 bags to do both based on 100 ft. or so.

Jaz
 
  #4  
Old 03-15-12, 08:32 PM
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Thanks for the response Jaz. No concern about a modified 'bonding' the hardi to the subfloor, rather than an unmodified used to just fill gaps?

Laticrete's site puts it in the 60-70sqft per pag, so i grabbed two of the 253 Gold 50lb bags for the modified (think they were ~ $25 each), and two of the cheap $7 bags of Laticrete 'Floor Adhesive'

even if i upgraded to the 'MegaBond' from Laticrete it would still be cheaper than buying a 3rd bag of the modified. that that being said, saving $20 overall on the project is not a concern if there is even a small advantage to one way vs the other.
 
  #5  
Old 03-16-12, 09:04 AM
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No concern about a modified 'bonding' the hardi to the subfloor
None at all. When I used to use concrete board for floors, I almost always used modified. The main reason was that I rarely used Hardie. I used mostly Durock & PermaBase, both recommend only modified.

You should use one bag plus a handful for under the Hardie. No big deal, with your plan though. You should get 75-85 ft. per #50 using a 1/4x3/8 trowel unless you waste some.

Jaz
 
  #6  
Old 03-16-12, 10:27 AM
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ahh ok, thanks Jaz. You said you 'used' to use cement board, you no longer use it?

Do you see any issue/difference if I keep the (cheaper) unmodified thinset for the hardi/subfloor layer?
 
  #7  
Old 03-16-12, 02:21 PM
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I use Ditra more than any other product for floors in place of backer boards. Keep doing what you're planning.

How about the joists, is the framing stiff enough for tiles? Is the floor flat?

Jaz
 
  #8  
Old 03-16-12, 03:46 PM
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yeah the 3/4" plywood is in good shape after we took up the 1/4" underlayment for the old tile. joists are 16"oc, on 2x10's.
 
  #9  
Old 03-16-12, 05:29 PM
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Chances are your framing does meet minimum deflection criteria for ceramic tiles, but there is no way to know for sure from the info you supplied. You also have to know the span of the joists. It would also be helpful to know the species and grade, otherwise you're guessing.

Jaz
 
  #10  
Old 03-17-12, 07:49 AM
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we pulled up ceramic tiles that have been there for 20 years. they were a pain in the butt to get up. that's a real test right there.

with that being said, they're 16" apart, and anywhere from 8 to 12ft long depending on the area (there is a little jut-out where the laundry is that make up the 12ft sections). even using 'unknown species, good condition' I get a deflection of L / 399 for the 12' spans.

I am going to swap out the Laticrete 'flooring adhesive' for a 3rd bag of modified, or 2 bags of megabond unmodified. two bags of this are still cheaper than a bag of the gold modified i'll be using for the tile and i still get to use an unmodified. question here is do I use this unmodified for taping the seams too, or should I mix a small batch of the modified to tape the seams then wait 24hrs?

- clean floor
- cut hardibacker, adhere to floor with thinset 1/4" notch trowel, screw every 8 inches
- wait 24 hours
- wipe top of hardi with damp sponge, spread modified thinset with 3/8" trowel, backbutter all tiles, press in firmly to install
- wait 24 hours
- grout
- wait 48+ hours
- seal grout

If I'm doing 6" and 12" tiles, I can use the 3/8" squared notched trowel for both?

Thanks again.
 

Last edited by skibum01; 03-17-12 at 09:05 AM.
  #11  
Old 03-17-12, 05:12 PM
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You should be using modified thin set for the seams. Some like to tape the seams as they set the tiles. One reason for this is so they do not create a speed bump, which could happen if you get sloppy.

There is no reason to wait over night to start tapping and/or setting the tiles.

If I'm doing 6" and 12" tiles, I can use the 3/8" squared notched trowel for both?
You have no choice, but yes, you want the tiles to end up at the same level..... no?

Jaz
 
  #12  
Old 03-17-12, 05:41 PM
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yeah, mixing 6" and 12" tiles is artistic enough for me... no need for different levels

i was under the impression i should follow what Laticrete has on their bag for the unmodified MegaBond, and wait 24 hours for it to set. I guess if you're screwing the hardi down over thinset, it's not going anywhere, especially with 80-100 screws per board. wow.

while the plywood is exposed, i want to toss a few more nails (or screws) in some areas. zinc coated screws or any specific type of nail?
 
  #13  
Old 03-17-12, 06:22 PM
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while the plywood is exposed, i want to toss a few more nails (or screws) in some areas.
Why only a few? You should be re-fastening the entire floor, into every joist every 8-10". 2"-2 1/2" screws or 8D galv. deck nails, or similar.

Jaz
 
  #14  
Old 03-17-12, 06:36 PM
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the subfloor is pretty solid, just a couple places where we had to put extra elbow grease into getting the underlayment up need some extra. i'll get some extra to toss into all the boards.
 
  #15  
Old 03-17-12, 06:46 PM
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the subfloor is pretty solid, just a couple places where we had to put extra elbow grease into getting the underlayment up need some extra.
That's the wrong attitude. :NO NO NO: Handymen that do that are called hacks.
You can't see minor movement. Squeaks mean movement, but today no squeaks, next week when the temps and humidity changes you may have them. So you may be fooled thinking everything is fine? They might be fine, but you don't know. Just do the entire floor and be safe.

Jaz
 
  #16  
Old 03-17-12, 07:06 PM
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alright. seems like screws would hold better than nails, just take a bit more time.

just a standard zinc-plated wood screw, galvanized? i wonder why most wood screws are philips, what a pain.
 
  #17  
Old 04-08-12, 04:19 AM
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Skibum take care of your thumb! Go with the screws
 
 

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