Ceramic tile over wood subfloor

[jackpine]

Hi I am new to forum, and and in middle of large tiling project; looking for some help. Here's basics: I am putting in ceramic tile over plywood underlayment, which is over t&g subfloor over joists on 16" center. The structure built in '55. The subfloor is 3/4" thick and the underlayment is 5/8" plywood installed with grain at 90 degrees to joists. I checked the structure and it meets the L/360 specs. The existing floors being removed are linoleum installed in 1984, which are fully glued to plywood, and mosaic wood glued to plywood. I've decided to remove the linoleum, which is slow and tedious work using heat gun and 8" scraper. I plan to put a 1/4" hardibacker board on thin set mortar over the plywood, and then put the tile on thinset over this. The tile is 12" Datile from Menard's.

Here's the main difficulties I'm having, which probably are no surprise:

See pictures for details.

1)The linoleum was glued down very well and is coming up slowly. There is still some backer residue and glue. How clean does this have to be to put down the hardibacker? What methods suggested to clean further?

2)The wood floor came up easy in most places. A few spots had some damage where the ply bond was weaker than glue bond. I would like to patch these instead of putting an added layer over the subfloor. There are height issues in the kitchen around dishwasher and refrig/cabinets. Again regarding the mastic left, how clean does it need to be; what methods to clean?

When the wood parquet floors and linoleum were put down in 85, I prepped the floor, which was creaky. So I renailed the plywood to the subfloor at the joists (maybe was a nono from what I've read). Overall still stable.

3) What type of thinset mortar should I use for the hardibacker to plywood and for the tile to hardibacker?

Thank you very much! I am going back to remove more wood floor and will check back in a couple of hrs.

Steve

[Brian in San Diego]

Steve,

When you imbed the Hardiebacker in thinset it's purpose is to fill voids under the Hardiebacker. I think I'd set the Hardiebacker as soon as you have finished breaking your back getting all that old stuff off your underlayment. Follow the manufacturer's fastening schedule and you should be fine.

Use modified thinset for both under and over the Hardiebacker. If you have HD anywhere around I would recommend using Versabond.

Brian

[jackpine]

Thanks for the suggestion Brian, I finished pulling the rest of the wood floor off this morning. In one area I'd used a different brand of mastic, it's darker and thicker. I've used a scraper on the floor that gets up some of the glue residue. From what you've said I should be good to go with the modified thinset under the hardibacker. The underlayment where the linoleum was is very smooth; should I scuff/rough up to get wood showing also?

Thanks, Steve

[CSS]

No you do not need to do anything to lino. to install backerboard the thinset is just to fill the voids so you have a solid surface without loose areas or pockets. the screws hold the board in place so you may use a unmodified under hardi if you want to save a couple bucks. if the $8 a bag diff dont matter the versabond is a good multi purpose thinset.

[Brian in San Diego]

James Hardie instructions specifically state to use a modified thinset under Hardiebacker. We try to encourage the DIYers to do it by the book.

[Trask]

Agreed..I don't have an issue with using unmodified thinset under CBU but you have no worries if you go by the manufactures recommendations. If Hardie wants Modified they have a reason...go with modified. Versabond is time tested and is economical.

[jackpine]

I am assuming that you put the nuheat matt down first and tape, then use thinset to float, and then put the DITRA on top. I just wanted to make sure how you are doing this. sounds like a great way to keep level.

[John Bridge]

Hi Steve,

You dug up an old thread here.

I would say (not being an expert) that you are correct. I have now done two heated floors, the one mentioned above and another over a concrete bathroom floor in my house.

In the most recent one I used Laticrete heating mats which are self-stick (pretty much). I used a hot glue gun to make sure they stayed down. Took a while but it was worth it. Then I floated over with thin set and left it till morning, whereupon I installed Ditra and left it alone again. Came back and set the tiles.

[cx]

Brought your post here from the old thread, Steve. If you'll keep all your project questions here it'll help folks see the history and what's been previously asked and answered.

'Fraid I don't know what TGR is.

And most heating systems don't require a CBU be installed over the plywood subflooring prior to installing the heating wire. You got something special in mind there?

The uncoupling membrane over the heating system is an excellent idea, though, to my thinking, even though most heating system manufacturers say it's not necessary.

My opinion; worth price charged.

[jackpine]

TGR was the username of the person who posted the technique of using the ditra and backerboard with nuheat rolls. I couldn't find a way to respond to that user, so I put the name on the post. Sorry for the confusion. Thanks for the additional info.

[jackpine]

I am still looking for advice on cleaning mastic off plywood underlayment. The last section of wood parquet floor I pulled up has a much thicker layer and it is almost black in color (from '86). There is also some remnants of old linoleum backing (greenish) that I pulled up at that time to put down the wood. Is scraping the best way to go; or are there any solvents that would help...I know there is downside to those. Thanks!

[jackpine]

My project has now another phase; my better half insists on in floor heat. I have studied posts and mfg websites, and I am looking at nu heat, step warmfloor, laticrete, thermosoft,warmly yours and easy heat. Have put in for quotes on them. About 250 sq feet to heat; floorwarming only. Thermosoft, warmly yours, and laticrete look similar; easy heat maybe a little cheaper. The nu heat and step warmfloor look easiest for installation. Theromsoft has a 50% off sale good through tomorrow; compared to other pricing actually is about 40% less. Any particular benefits or cautions with any of the manufacturers that you folks know about? Or any tricks for installation?

Thanks!

[cx]

Steve, if you're gonna put a CBU over your plywood, using a chemical remover to help get the cutback adhesive (the black stuff) off isn't so much of a downside as you'll not be trying to bond anything to the floor.

But if anything is to be bonded, a membrane, heating system, SLC, you need to scrape the stuff off dry. Or remove and replace the plywood.

There really are no easy methods with that stuff.

For heating systems it's mostly dealer's choice amongst those you've cited. We have folks who've used most all of them with success. Thermosoft doesn't ring any bells for me, but that doesn't mean much.

My opinion; worth price charged.