Questions on glazed porcelain on cement slab

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Old 12-03-14, 02:58 PM
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Questions on glazed porcelain on cement slab

I have several questions. I have searched a lot and watched lots of videos, but still some questions remain. Please take a stab at any or all!

I will be tiling my home's entryway, which is an L-shape. When I moved in, a low pile carpet was glued to the subfloor. I tore it up and found the cement slab, covered in black (mastic?), and there are square imprints, which I am guessing are from a previous tile installation. Photos are below.

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This is the tile I will be installing.

My Questions on preparing the substrate:

#1 Does this have to be scraped and somehow removed to prepare it for porcelain tile?

#2 Since it may be very difficult to remove, would skim coating it with cement or using self leveling cement as a skim coat be an option?

#3 Would it be better to install some sort of cement board over the whole thing?

Regarding tiling:

#4 Is the mortar chosen based on the substrate or the tile?

#5 Sanded grout for this installation?

#6 Is a transition piece needed for the front door? Or is the base of the door frame adequate? Please take note of the semi-exposed hot water pipe.

#7 What size trowel? The tiles are 12" x 12" and the floor area is 60 sq. ft. in an L shape.

#8 Let's say I find some accent tile that I want to create a border with. Must it also be porcelain? If it's ceramic, would I still mortar and grout as usual? If I found a cool mosaic made of stone, marble or even glass, is it possible to do?
 
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Old 12-06-14, 05:04 PM
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Any takers? Ideas? Thoughts? Questions?
 
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Old 12-07-14, 04:52 AM
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I'm new to tiling myself so I don't have any absolute answers for you.

Read the product descriptions to find out about how to deal with the previous adhesive material. The self leveling compound I just used says yous can install over adhesive as long as it is not sticky. There my be different advice for the use of thinset.

You can mix and match different tile materials. The thing to keep in mind when doing this is how to deal with different tile thicknesses. Stone tile usually runs thicker than ceramic tiles. But they can all vary even the slightest amount between different style of tiles.

Which thinset to use? I have no idea. I'm using unmodified for my project which includes marble and ceramic tile. I f you are using all ceramic/porcelain, I think modified is the way to go.

The type of grout you use is based on the size of the grout line. I forget the dimension, but I think it is if the gap is less than 1/8" you use unsanded.

Tile up to the door. Cut your casing so the tile fits underneath.
 
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Old 12-08-14, 02:00 PM
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Thanks! I've downloaded all the product info I could find on the tile and didn't find anything on prepping the substrate. The black stuff definitely is not sticky. It seems like its been there a LONG time. It's been exposed to the air for several months now and nothing has loosened up between my dogs and me walking over it daily. I'm concerned that any mortar will have problems adhering to it. My hunch is to do a skim coat of cement so the thinset has something clean to grab onto. But, this is my very first tile project and I wanted to get other opinions. I feel like I've searched until the end of the internet for answers, but sometimes all you need is the advice and knowledge of someone who's done it before.

I appreciate your thoughts on the different thicknesses of materials. Unless I come across a truly unique accent that I have to include, I'll probably just go straight with these 12" x 12". Might be better for a first timer, anyway.

This is a project I want to do once and not have to deal with tiles popping or cracking because I didn't do things the right way. I am all for learning from mistakes, but I'd rather they be mistakes I can fix during the process, not six months after.

Thanks for your input! Hope your project is a success!
 
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Old 12-08-14, 03:55 PM
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I meant the product info for the thinset and self leveling cement.

This is one of the products my local Lowes sells: Tile Mortar | Flooring Mortar | TEC Skill Setâ„¢ As one of the suitable substrates listed: "Adhesive residue (except tacky or pressure-sensitive adhesive)"

You may need to back butter your large tiles. Check out the Floor Elf's web site. I found the informations there to be helpful.
 
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Old 12-08-14, 04:27 PM
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Oh, gotcha. I didn't know if the concrete substrate determines what type of mortar is used, or if the material of the tile does, so I haven't looked at mortars yet. I don't think the slab needs self leveler, but if I were to skimcoat it, I would use SLC to make things easier on myself.

I will check out that website. Thanks!
 
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Old 12-08-14, 07:02 PM
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This is none of my business so please ignore if it's inappropriate: there's a conversation parallel to yours, currently on p.1 (you're on p. 2), on a different tiling project. It was started by drooplug on 8-8-14, going back and forth with czizzi who seems knowledgeable, in case you want to eavesdrop...
 
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Old 12-08-14, 07:22 PM
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Should have said: drooplug's other thread is titled How to install tile? and of course now the threads have swapped places, FirstHomeNH. (Sorry, I haven't figured out a better way to indicate threads yet, I'm very new.)
 
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Old 12-09-14, 04:04 AM
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Thanks Mary, nice to see my name used without prompting.

The black stuff definitely is not sticky. It seems like its been there a LONG time. It's been exposed to the air for several months now and nothing has loosened up between my dogs and me walking over it daily.
The key here is that the mastic is hard, stuck fast and not going anywhere without chemical strippers. I therefore would liken the presence of the mastic as similar to an uncoupling membrane such as RedGard or Hydrban. In that case, I would use a latex modified thinset such as Ultraflex 2 by Mapei Products. Latex modified thinsets are stickier than unmodified ones and should grip what you have well. I would refrain in your case from the addition of another layer such as a self leveling compound to keep the "sandwich" as simple as possible. Limit Leveling and patching to those areas that are out of level (dips and valleys). I would also recommend back-buttering your tile to make sure you get excellent coverage.
 
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Old 12-09-14, 01:29 PM
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Hi Mary, thanks for pointing me to that thread for czizzi's insight. I didn't read that the OP had a similar substrate or installation as mine, unless I am missing something? Maybe it was the wrong thread title?

Hi czizzi. After getting started with drooplug's suggestions to research the specs for mortar, I was able to uncover a whole world of info that answered some of my questions above.

I have finally identified my black mess as asphaltic cutback adhesive, likely filled with yummy asbestos. I have read that there are some mortars that are indicated for use with cutback, although it still has to be scraped down some, but only to the extent where there aren't ridges. I believe the cutback is mostly absorbed into the concrete slab and what I've read thus far indicates I need to shot blast it, which will then require some SLC to smooth it. Can I ask the rationale for scraping opposed to encapsulating? I'm a person who needs to know the "why" before I can move on in my head.

During my research, I discovered Custom Mega Flex Crack Prevention Mortar, but I think this would need to go over cleaner concrete. Is this comparable to Mapei Ultraflex 2? Do you know of these elusive mortars that can be used on cutback?

I've downloaded and read RFCI's recommended work practices for removal of resilient floor coverings, and to be honest, I am not willing to go to that extent to remove this stuff. Even if that means putting carpet over it rather than tile. I'd REALLY prefer not to carpet it, as the stuff I pulled up was damp and smelly, and it doesn't feel right, with our cold and wet NH winters, complete with wet boots and paws. I've read where some installers have tiled right over cutback and haven't had any issues. What are your thoughts?
 
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Old 12-09-14, 01:50 PM
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No scraping, sanding, blasting or anything to disturb asbestos cutback. The less you disturb the better.

Can I ask the rationale for scraping opposed to encapsulating?
Hint - By tiling over it, you are in fact encapsulating it.

Again, if the cutback is stuck, solid and well adhered, a modified thinset will work fine. If you do not have a slab that has a lot of movement (cracks) then you do not need an expensive mega flex crack prevention mortar. I have used the CBP's VersaFlex mortar in a pinch, however, I prefer UltraFlex2 as my go to. It mixes to a smoother consistency and is easier to work with. I find the mortars carried by box stores to be sometimes suspect due to the liberal return policy. A bag could have been sitting for 8 months and ends up returned. I pick it up and it has lumps and won't mix smoothly. You probably would not notice the difference, but I purchase most all my supplies from tile stores/distributors. The tiles are square (not a pun, but actually square) and tile backer is not picked through and ragged, you don't have mixed dye lot issues, and the mortar mixes are fresher.
 

Last edited by czizzi; 12-09-14 at 02:36 PM.
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Old 12-09-14, 02:04 PM
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Hint - By tiling over it, you are in fact encapsulating it.
That is true!

I don't have any cracks in the slab at all, just some divots from long ago carpet tacks, and not even the most recent carpet. So it sounds like Mega Flex might be overkill, not as budget or DIY friendly as UltraFlex2. Is there any sort of test I can do to determine if I really can set tile directly over this? I read somewhere that if you can get a fingernail underneath the adhesive, it has to be scraped. My cutback is really set in the slab, to the point that when I first uncovered it last year, I gasped and thought it was mold!

The slab has to accept water penetration in order for mortar to adhere, is that correct? No beading. Is there a time frame that it should absorb water? Like if I "pour a few ounces of tap water and time it to absorb" type of test?
 
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Old 12-09-14, 02:35 PM
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Is there any sort of test I can do to determine if I really can set tile directly over this?
I forbid you from overthinking this... The modified thinset spec sheet states that it is OK to use over cutback adhesives. It is possible that the CEMENT needs to be porous for proper adhesion, but you are not adhering to the slab, but the cutback. Recap- Cutback stuck fast to slab---> modified thinset ok on cutback---> move on to planning your tile project.

Don't worry about the small divots from the carpet tack strips, your tiles will float over those. Any large craters will need to be filled with a cement based patching compound like Speed Finish by CBP. And, as a bonus, you have already got a nice grid marked out on your floor to guide you during your installation.
 
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Old 12-09-14, 03:59 PM
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as the stuff I pulled up was damp and smelly,
Why was it damp? You may have a leak on your hands that needs to be resolved before you tile.
 
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Old 12-11-14, 10:33 AM
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Thank you for saving me from analysis paralysis. I love to research and learn, and sometimes having too much info as an amateur can be a detriment. Too many what ifs piled onto no experience.

Drooplug, there's no leak but I have moisture issues throughout the house, originating from the dirt floor basement. Some moisture, no doubt, is also coming through the slab (the first part of the house is slab and the rest has a basement). The entry (which is what's being tiled) had a mildew odor, and when I pulled up the carpet, the carpet was damp underneath. Once I disposed of the carpet, the mildew smell is gone.
 
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Old 12-11-14, 02:33 PM
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You'll want to verify that you are not getting moisture from an improperly sealed entry door. Take a good look at the areas on the outside that are within 2 feet of the floor and make sure that you have an adequate seal to prevent future moisture from getting to the inside.
 
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Old 12-11-14, 03:36 PM
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The mildew odor is gone because the mildew was growing in the carpet. Now much in concrete for mildew to feed on. How high above the ground is this concrete slab?
 
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Old 12-13-14, 12:56 PM
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Pretty sure the door is sealed adequately, but when the previous homeowner had the area just outside the door paved, it was paved LEVEL to the interior. My home inspector noted this and thought it could be an entry for rain. They may have done it that way for wheelchair access.

The house is built on a slope, with the entry at the highest point. The slope continues down the length of the house, so the other end of the house is the highest off the ground. So the slab is likely level to the ground at the entry, and possibly a few inches up at the end of the slab.
 
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Old 12-14-14, 07:26 AM
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If you refer back to your original pictures, the staining on the back of the carpet/pad point to the spots of most concern with moisture. Looks like the center of the door and the latch side show the most staining. That would be worthy of further investigation.

You noted wheelchair access as to slab at grade. Have you verified that you have sufficient clearance under the door to install your tile? Doesn't look like you have much room to work with. Test by laying one of the tiles on the floor and operate the door. It should clear the tile. Do this throughout the complete swing of the door, from closed to totally open.
 
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Old 12-28-14, 10:55 AM
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Sorry I've been away from the thread. I haven't made any progress other than buy more tile, so I haven't taken off! There is enough clearance at the door, thankfully. And since removing the carpet months ago, I haven't observed the slab being wet or any area leaking. Just the typical melt from my boots after I come in from snow shoveling.

I'm feeling pretty good about it. I haven't tried laying the tile yet for pattern/direction, although I do think straight on in the L-shape would be best not only for the area, but for a beginner. I MAY have enough tile to also do the kitchen, BUT I have decided I want underfloor heating for the kitchen, so that will have to wait.

Oh one question I do have is there will be two adjacent rooms to the entry that is being tiled, but the flooring for one is undetermined and the other is the kitchen, which would be installed at a later date. How will I handle the transitions on these?
 
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Old 12-28-14, 12:34 PM
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Are the transitions open archways or door openings that need to be accounted for? Open archways would plan for a transition around midway between the jamb. Door openings shoot for a transition that falls under the closed door so that it is not visible from either side.

Knowing what flooring is going to be used in all areas helps to plan. The kitchen with the same tile will still need a transition as you are including a heating mat which will add thickness to the floor and the two will not marry very well. A thick marble transition could be the answer, they make ones that are thinner on one side compared to the other making a natural ramp. THe other room will need more planning depending on what you plan.
 
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Old 12-28-14, 02:52 PM
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Let me first preface this by saying my home is a work in continual progress, and I've only been in it a year.

That said - the entry to the kitchen is an open archway now, BUT I plan to put in a door at some point. Which I guess now begs the question - should the door go in before the kitchen floor? And it is possible that I won't continue the same tile from the entry, only because when it comes time to do the kitchen floor, I may want something a little more aesthetically pleasing. The tile going in the entry way was on clearance at the Depot, and I couldn't pass it up, especially with the currently exposed cutback.

The other transition is an actual door, it is part of the slab of the entry way and is currently covered in the same carpeting that was in the entry way. I plan to make this room a closet/dressing room, so I think a plush carpet would be best in there.
 
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Old 12-28-14, 03:01 PM
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For the kitchen archway soon to be a doorway. Simply lay out your tile such that you have a couple of small pieces across the opening and not too far into the foyer. and finish the floor for now. Keep several extra tiles on hand so that when you do go to finish your kitchen, you can pop off those couple tiles and refinish for an appropriate transition to whatever you have in the kitchen.

If a transition to carpet in the other opening, finish your tile with a Schluter edge piece and tuck your carpet up to it.
 
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Old 12-28-14, 04:51 PM
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Ok, that makes sense. Thanks!
 
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