I'm a bit confused on a underlayment issue. I have already bought Laticrete Megabond and the Laticrete additive. I also already have sheets of "luan" to lay down. I intend on using Hardibacker on top of the "luan". Laticretes website says not to use the megabond on Luan but to use a EGP. The luan I bought has a Type 1 exterior glue rating. The guy at Lowes assured me that the term "luan" has just become a generic term for plywood underlayment and that what I bought is correct.

My floor consist of 2x10 joist 16"o.c. 23/32 OSB subfloor, 1/4" EGP, 1/4" hardibacker, then tile. Does this sound good?

Your statements are a little confusing. I will do a little assuming and answer you as best I can. "Lauan" (its correct spelling), is forbidden anywhere under a tile installation. The odds are you're wood is 4' x 4' "MultiPly", which is a brand of underlayment that's sold in many/most or maybe all Lowe's Stores. If so, you don't need anything else. "Modified" Thin-Set should be your choice to install ceramic tiles to this and any underlayment substrate. "Lauan" has never been, nor will it ever be, a "Generic Term" for anything, especially "plywood". "TIRTGIM" Armen Tavy

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Armen Tavy

Sorry I didnt mean to be confusing but that is basically how the info was given to me.

The sheets I bought were 4'x8'. The tag that hangs on the rack where the sheets are stacked said "Lauan underlayment 1/4" type 1 exterior glue plywood." There was also stickers on the sheets that said "exterior grade". Seems like their tag contradicts itself. This stuff looks to be made up of 3 layers.

Hopefully its the right stuff because I already layed it down.

Thanks for the response.


Edited by Brian Jones on Jan 30, 2009 at 12:16 AM


Edited by spacerman on Jan 30, 2009 at 12:40 AM


Edited by spacerman on Jan 30, 2009 at 12:40 AM

I will try to stop at my local Lowe's to check it out. However, the word "underlayment " doesn't necessarily mean it's an "underlayment" for ceramic tiles. The words, "exterior grade" only refers to the glue between the 3 layers. If the "skin" (top layer) is really "Lauan", there isn't a mortar in the world that will bond to its surface. Armen Tavy

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Armen Tavy

If it's "Lauan" your only option is to use my TAVY "Thin-Skin" which "Will" stick/bond to "Lauan". However, "Lauan" and water/moisture are not "bedmates". Armen Tavy

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Armen Tavy


Edited by spacerman on Jan 30, 2009 at 06:41 AM

I dont know if this may be a sign as to what it is but it was about $8 for a 4x8 sheet. Like I said before, I hope its the right stuff because I already layed down the sheets along with my hardibacker.

It's all a mute point now since you already installed the Ply "Something" and the HardiBacker over it. In essence what you did is make a "Baloney" sandwich instead of "Roast Beef' with Swiss Cheese. I hope for your sake that you used mortar or adhesive to secure your HardiBacker Boards before you secured them with nails or screws. If you did not, you must remove the "Hardi" and re-install it properly or your tiles will crack in short time. Did you leave a 1/8" space between all the "Hardi", backfill the spaces with modified mortar, then use Alkali Resistant backerboard tape over the joints with yet another coating of mortar over the tape? The triple decker sandwich was VERY GOOD, its the Filling along with the Toothpicks that hold the sandwich together, that may compromise the quality of this meal. Let's hope the wind will fill your sails.
"TIRTGIM" Armen Tavy

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Armen Tavy


Edited by spacerman on Jan 30, 2009 at 05:44 PM

Pretty much a YES to everything.

I used mortar under the Hardi then used the Hardi specific screws, left the spacing between boards then filled and taped the joints with a coat of mortar over the tape.

How great of a job does the coating of mortar need to be over the tape. Obviously not creating a lump from to much but does it need to be as good as say, mudding drywall? I will have to go back and sand the seams a little bit.

Thanks for all the help so far.
Edited by Brian Jones on Jan 31, 2009 at 02:08 PM


Edited by spacerman on Jan 31, 2009 at 03:16 PM

Only a skim coat. Just enough to hold the tape in place. The Alkali ResistanT Tape is perforated and the mortar should at least fill the perforations. Of course we dont want humps to tile over. Good Luck, and keep us all in the loop so others can benefit from your experience. I have done my job right if I can convince others to step up to the plate and "hit a home run" without errors. Armen Tavy

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Armen Tavy


Edited by spacerman on Jan 31, 2009 at 03:16 PM

Armen Tavy,
Make any money on those spacers yet? I imagine Armen Tavy is a grade a old school tile guy. The new school knows that multi-ply burned down, and lowes does not sell "good" anything (except those spacers)for the professional. looked to me you may have given yourself a height issue with all that floor. i believe you only need 1 1/8 thick subfloor. how you get that should include 1/4 cement backer board. if it doesn't you can use schluter ditra. or they make a thinset you can put down on wood with no underlayment that solves height issues. thats right, 100 dollars a bag but that guarantee it above grade on osb. email floormesales@gmail.com for all your flooring needs.

Thank you for the "un-soliceted TAVY Spacer" plug. The "Industry Says" that the "Minimum" sub-floor thickness should be 1 1/8" BEFORE any other tile underlayment is used over it, including any kind of membranes and "cementitious" Backerboards (CBU). "CBU" does not strengthen a floor to the required stiffness, as does full sheets of plywood (fastened correctly)and other "woods", except "Lauan", which has been totally "Banned" from use in the Tile and Linoleum Industry.

When tiling over "Plywood", it should be "Exterior Grade GLUE Plywood", however, the "Tile Industry" doesn't really favor installations directly over any kind of WOOD subloor. 3/4" minimum "Mud Pack" over Galvanized Wire Lath, "CBU", and other "TCNA " Tested and Passed Tile Underlayment Membranes over a 1 1/8" sub-floor, is the only "Politically Ceramic Way" to go. Armen Tavy "TIRTGIM"

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Armen Tavy