Anything in a bucket premixed should NEVER be used.

Unless it is in a bag and you need to add water, do not use.

Although the manufacturers say the premixed junk is "OK" for showers, it is inferior to "real" thinset, and should never be used. It is organic, and can create mold when wet. And some manufacturers claim their product is mold resistent, but do not trust that either.

Check the ANSI standards too depending on your application. Know your tile and the thinset required. Example - Porclain MUST and should be latex modified thin set that is 118.4 ANSI rated. I have not found a bucket of pre mix that has this ANSI standard.

The premix stuff never really hardens either, it remains soft for a long long time. Many contractors like it because it does not need to be mixed and you can put a lid on it and reuse it at a later date, but that does not make it the best choice.

I would question any contractor that is using this stuff. Ask more questions before you hire him.

Tom, thank you for replying so quickly. I had that sinking feeling when I read his quote.

The rest of his install method will be 1/2" Hardibacker on studs in wet areas (Greenboard in dry areas), with Redguard over the hardibacker before tiling.

This is for a tub surround (4x4 inch ceramic tile with a 6" mosaic strip) in one room and two shower walls (all glass mosaic) with acrylic base in another room. From what I have read on here, Redguard sounds acceptable in these settings (versus a vapor barrier). Is this right or have i misunderstood?

Thanks very much for taking the time to help.

All mastics are not created equal, but there's not a mastic made since the early 70's that could be used in wet areas safely. Tell your guy that if he uses one of the new lightweight thinsets (Mapei Ultralight, Laticrete 255, or Custom Megalight), that he can still "hang" the tiles from a level line, just as he does with mastic, and they won't move on him.

Good stuff. :-)

Thanks, these sound good, I will get one of these.

Tom, your note about questioning the contractor makes sense. We also want to tile over hardwood flooring in kitchen and dining rooms (about 350 sq ft). The same tile guy told us he would do: mortar, 1/4" hardibacker, mortar and then our tile (12" porcelain). We've just been reading on John Bridge's that this sounds like a bad idea.

Tom or Bill -- do you know a good tile contractor in Atlanta, GA?

The hardwood's got to come up. It's too unstable to til over, even with the cement board.

Bill, we also used the Deflectometer on the John Bridge website. Our kitchen will be 14' wide (this is a 1950s ranch we have just bought and we are moving the kitchen into what was the original living room).

I need to check whether we have 2x8s or 2x10s, but either way, the deflection rating was well under what is needed for porcelain tile (L/153 for 2x8, and L/290 for 2x10).

So, to tile it we would be looking at taking out the existing hardwood floor (which runs through kitchen and dining rooms), and reinforcing these joists. Can we place posts under every joist half way (7') along (would this then give us joist lengths of 7' to use in the deflectometer?), or must we sister all along the length of the joist? I remember reading threads on this some time ago on here but i think they have dropped off.

The other option would be to refinish the cat-pee-stained hardwood floor and embrace it as our kitchen/dining floor. We much prefer a tiled kitchen floor, but perhaps this is the best way to go now.

My last (and most naive!) question -- if we just leave the hardwood floor and don't tile, will there be any problems with the joists supporting the weight of the kitchen appliances? These will be placed closer to the edge of the room above a central supporting wall, so I guess they will have a different load distribution than a tiled floor would, but they are pretty heavy all the same. is this a concern?

thank you

First, you want to check what you have for joisting. Code in most every area I know of is for the deflection standard to be L/360, no matter WHAT kind of flooring it's going to receive. I don't know how old your house is, but unless it's 50 years old or older, your joisting should be okay. Check it to make sure, though. Most houses that have that kind of span are using 2x12's or their on center spacing is reduced to 12" on center instead of 16". One other twist alot of builders are using is instead of using traditional dimensional lumber for the joists, they're using "I" joists, or another kind of stronger member-- I'm drawing a blank here. Brain farts-- I HATE EM!! LOL Someone will have the name of them. This is embarrassing, because it's elementary!! But one way or another, this other "member" if engineered properly, can carry spans over 25' or more.

Bill, we just went to the house to look. Under the kitchen/dining hardwood floor are 2x10" joists. Do the other types of supports (i-beams, and is the other type engineered trusses?) look similar or are joists clearly different looking? If so, we have joists.

The 2x10s are 16" apart on-center and they span the 14-foot wide room (which is combined about 27 feet long). But, several of the joists have previously been sistered (with 2x10s) and there are 2 concrete stacks underneath 2 of the joists half way across the 14-foot span and about 1/3 and 2/3 along the length of the room.

The house was built in 1956 (and not much has been updated since!) so code probably doesnt apply.

How do we determine how much sistering/supporting is sufficient to bring the floor deflection down to the levels needed for a ceramic floor?

Even if it would be OK, we'd need to take out the existing hardwood floor and put down plywood. Unfortunately, because we believed the tile guy who told us we could do backerboard and tile over the hardwood, we have had our carpenter frame a wall on top of the hardwood to separate the kitchen and dining rooms. People warned us that a fixer-upper would not be easy ;)

Okay-- first things first. As for the wall being built on top of the hardwood, you should be able to cut the hardwood on either side of the wall with a reciprocating saw (sawzall). As for sistering up, you're not that far off from where you need to be. With 2x10's, max span is thirteen feet. You could probably sister either 2x4's or 2x6's to the joists that aren't sistered already. OR, you can take a 44 beam and jack it into place at mid span with a couple of adjustable lollicolumns. That would also be more than enough for what you need.

Oh, and yes-- TRUSSES is what I was looking for!! DUH!! :-)

thanks Bill, maybe our tiled kitchen floor is still an option. we will talk to our carpenter for quotes on the sistering/beam.

Now, if we could find a tile guy who knows what he's up to...! I will post on the john bridges forum as you suggested. thanks so much for your help, its such a relief to hear advice from someone who knows their profession.

I have 12x12 porcelain tile half way up a 4x4 shower surround. Used mastic (Reliabond ceramic adhesive Type I BIG bucket)over waterproof fabric brushed with liquid waterproofing (black stuff). Most forum posts say thinset is what one should use. Bill Vincent seems most sensible and now I am wondering if I should take all this tile off and start over using thinset? Any suggestions?

Thanks, Gail

I would if I were you. You have two things going against you. First, mastic shouldn't be used in a wet area. The reason is that even after it's been dry for years, it can still reimulsify (become soft) from contact with moisture. Secondly, even in dry areas where mastic CAN be used, it's not supposed to be used for anything bigger than 8x8 tile. The reason for that is that if you apply mastic too heavily (as you would need to with the larger tiles-- anything bigger than 1/4x1/4 is too big for mastic) then it won't dry, and if you use a 1/4x1/4 notch then you're not getting the coverage you need to have. So now, either you don't have enough adhesive behind the tile, or it's going to stay soft, which means it'll wash out from behind the tiles all that much quicker.

Take the tiles down.

Bill,
Yep, I thought you might advise that. OK. I assume I need to scrape ALL of the mastic off the walls. That should be fun! You must be on the east coast - I'm in Washington state.

I need latex modified thin set rated at 118.4, right?

Thanks again!
Gail

Exactly. On ALL counts.

Hi all,
Just thought you would like to know that I have spent today brushing on Klean Strip Adhesive Remover on my shower walls and the mastic is coming off. It requires two or more coats but is ready to scrape within the stated 30", and doesn't seem to be affecting the waterproofing too much. I think if I let it dry overnight it will be ready to accept the thinset. I'm going to switch to 6" tiles as well. Thanks for your help! Gail

Wow gailsm, and I was peeved to have to spend a couple of hours cleaning silicone residue off my tiles and tub.

Good for you for doing it right. Good luck with teh rest of your project.

I hope that adhesive removeer wasn't solvent based. if it was you may have issues with the thinset sticking to it.

Hi Bill - well it was solvent based....I have painted another coat of waterproofing on and let that dry, and I'm going to bite the bullet and try laying the first course tonight and see what happens. I'm going to just take a wee bit of the dry thinset, mix it with water until I get a moderately stiff mix, and just go for it!

And "budge1", I got drywall mud and mastic residue off the acrylic shower base and the vinyl window frame with nail polish remover.

All this because the tile folks assured us the mastic was "suitable for wet areas", just like it says on the bucket. Ha! Gail

That's something that burns my butt. Every pail of type 1 mastic says it's suitable for wet areas, and yet every single thinset, grout, and adhesive manufacturer is well aware of the failure rate, and won't have any qualms about warning you against using the mastic for wet areas. However, sales people who have no intelligence and even less scruples have no problem selling it. No one wants to be the first company to take that phrase off their bucket of mastic.

Hi Bill - Yep, and we learned the "hard way. What a shame that disinformation perpetuates costly and frustrating errors and ultimately damage in people's homes, when often DIY is a result of not being able to trust "pros". Thanks for being such a valuable and generous resource.

So! The Thinset went on the waterproofing just fine, the tiles are set and plumb and straight (that was 10 hours of work between the two of us-one buttered and the other set). Today we tackle the one piece granite shelf that we had custom cut to fit into the window recess as well as between the side walls of the shower stall - that will require grinding the sides a wee bit...we'll post some pics if you like when we're finished! Gail

Please do!!