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insulatorpro 08-21-2008 06:10 PM

What comes first Leveling or backerboard
I'm in the middle of a bathroom makeover. I removed all of the old 3/4" pine board subflooring (mostly rotted from years of leaks). I reinstalled the 3/4" Home advantage moisture resistant plywood from HD! The floor is out of level by about 1/2 to 1" in spots. We bought marble tiles for the finished floor. The question is should I level the floor completely with thinset first. Then after that is cured, add more thinset then backerboard? OR Should I lay the thiset and backerboard to the plywood, then proceed to level the floor with more thinset or SLC. THANKS!!!!! Also, the bathroom is only 6' x 8', so a few extra dollars for the RIGHT material shouldn't be an issue!!!!!! Thanks Again!

Bill_Vincent 08-21-2008 08:55 PM

backerboard first, then SLC.

JazMan 08-21-2008 09:09 PM

Hi Mike,

First of all, although it's nice to have a level floor to install tile on, it is not mandatory. What you need is sturdi and flat.

Secondly, to install marble tiles on your floor, you will need to install another sheet of plywood. This underlayment can be as thin as 3/8", but I recommend going as thick as possible.

You can then install a 1/4" tile backer and then level the floor with SLC. (You can NOT level a floor like yours with thinset mortar.) Or you can use the SLC and then install Ditra or NobleSeal CIS.


insulatorpro 08-22-2008 07:51 AM

Thanks Guys! Hey Jaz, can I use the particleboard underlayment or should I get regular plywood? Also, should I use an adhesive to bond the layers together or would just screwing it be ok? Any preferences on SLC? I know there are a lot out there to choose from. THANKS!

JazMan 08-22-2008 09:01 PM


There is no such think as particleboard "underlayment". Particleboard is junk and can not be used on a floor for ANY application. Maybe you meant to say OSB? Use good quality plywood made with exterior glue.

Do NOT glue the underlayment to the subfloor, unless you can use a liquid type wood glue spread 100% and are able to fasten it super fast. Usually take 2 exp. people. Never use any type of adhesive that comes in a tube. Doing so actually creates voids and makes thing worse.

I don't use SLC enough to have a preference. I'm sure they all works as described. Just follow directions to a T, and don't expect miracles. You may need a primer. You will have to be prepare and work fast. Have enough material on the job, running out creates problems.


AtlanticWBConst. 08-23-2008 07:09 AM


Originally Posted by JazMan (Post 150961)

There is no such think as particleboard "underlayment". Particleboard is junk and can not be used on a floor for ANY application. ...Jaz

Evidently this home owner never got that memo:
(Small portion of one of our Remodeling projects from this week)

insulatorpro 08-23-2008 08:54 AM

HOLY CRAP! Plywood it is!!! THANKS!

JazMan 08-23-2008 08:54 AM

Yes I know......:furious:

Throughout history, people quest to save money and so discover new cheaper products to replace older, proven, but more expensive ones. I too have seen particle board used as subfloors and underlayment, many, many times.

Often these cheaper products are touted by jerks.....ah ahahahahhh, clerks at lumber yards. I'm sure the same clerks who referred to greenboard as at first "water-resistant" and later insisted it was "water-proof drywall" :censored: They had, and some still have no clue.


insulatorpro 08-24-2008 09:45 AM

One More thing. Can marble tiles stand up to the weight of a cast iron radiator, or should I reinstall and then tile around it??? The thing must weigh 3-400 lbs. Thanks!

roncudz 08-27-2008 03:25 PM

Be extremely careful with marble flooring. Pet urine will eat holes in it, plus completely ruin the surface shine. Bowl cleaners and many other cleaning products contain acids that will also remove the shine from marble. I made the mistake of installing marble flooring in our bathroom. It's just not practical flooring material. Nice for museums and masoleums though.

jogr 08-27-2008 03:46 PM

Just one point for future reference. It would have been best to do the leveling before the subfloor was applied rather than afterwards.

insulatorpro 08-29-2008 05:16 AM

Do you think I should level it before I put down the second layer of plywood? What would be the best way to do this? What would hold up to the weight?

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