Ceramic tile over wood underlayment? Will it stick?

[zaz]

We are having a difference in opinion between two different tile layers about our laundry room floor. We had someone come to the house who put down 1/4 inch wood underlayment that was nailed to the laminate floor underneath. Then he used ultraflex 2 mortar to apply the tiles (putting mortar just on the floor not on the back of the tiles). So basically this guy disappeared for about a week and has been a nightmare to work with so we decided to call someone else to finish the other two tile projects in the house. The new tile guy came to the house and looked at the job that had already been done in the laundry room and said that the mortar will soak up the moisture from the wood underlayment and cause the tiles not to adhere properly, causing the tiles to move and therefore the grout to crack.

I'm obviously not a tile layer and have no real clue on who's right here. Does anyone have any advice on this??

Thanks
zaz

It sounds like 1/4" lauan was installed, which is a no-go in the ceramic tile trade. You mentioned it went over a laminate floor. Did you mean a vinyl floor, or is it a laminate floor like Pergo?

Any chance that you know what is below the laminate/vinyl? How about the floor structure below? Joist size, spacing and type of joists?

[zaz]

Rob -
Thanks for your reply. I miss spoke the wood underlayment was nailed on top of linoleum. The underlayment was multiply plywood. What is lauan and why is it a no go with ceramic? Is this different than what he used? What do you think and what would you do now that it's installed?

Thanks so much
zaz

[bbcamp]

Luan is a relatively cheap plywood made from tropical hardwoods. It is weak, and sometimes bleed oils from the wood. It is not an approved underlayment for ceramic tile.

Multiply plywood may or may not be acceptable. It must be rated Exterior or Exposure 1. The glue laminating the plies must be waterproof. The knotholes in the plies must be plugged. Acceptable grades of plywood are AC, BC or CC (plugged and sanded). To my knowledge, there is no 1/4" thick plywood that meets these specifications.

Installing the plywood over a lineolum floor is OK, but not if it is vinyl. Lino is very hard and not cushioned, but most vinyl sheet flooring is. Cushioned flooring will "give" a little under point loads, this is not a good thing for tile. Are you sure you have honest-to-gawd lineolum?