mix/method for mortar bed (slate entry)
Hi,
I’m planning to set quarter-inch slate tiles (12″-square) in an entry, about 80 square feet. It’s on a concrete slab, and the finish level will be 1 1/2″ to be flush with adjacent wood flooring (already installed).
Have decided to do a mortar bed and will mix it myself. What’s the ideal ratio of sand to portland cement? I’ve checked around and it seems that 3:1 sand-cement is typical. A very experienced and skilled local mason (but not a tilesetter) recommended 4:1 for a mortar bed and suggested subsituting Acryl 60 for half the water (to reduce shrinkage during the curing).
Would adding some lime make a mortar less prone to cracking (higher lime content permits more expansion/contraction movement I’ve read)?
Seems to me that compression strength is not really an issue here–the only loads will be people walking, a bench, and some furniture. So adding lime seems logical. Less cement/more lime means trading compression strength for flexibility, according to the stuff I’ve read.
I will use galvanized steel mesh in the bed as well.
Any experienced pros out there?
Thanks,
Ed
Edited 6/13/2003 3:45:03 PM ET by MONSIEUR_ED
Replies
Me...I'd buy bags of premix concrete. Build it up about an inch..if I'm reading that part right.
steel trowel that smooth. Let it set.
Then set the slate with latex modified thinset mortar...
or if I wanted bullet proof.....as some slate is tough to adhere....
kerabond mixed with keralastic.
Jeff
Buck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
I've seen professional tile setters use beds as think as that. I've set quite a bunch of tile over the years but always over backer board which is not applicable to your outdoor setting. The mortar bed is the way to go. If I were to do it, I would probably do it in two lifts because of the thickness of the bed. I suspect you could use thinset over a built up bed if the back side of the tile is not too uneven.
good luck...
Denny
Actually this is interior--just inside the main entrance. Kind of like a mudroom.
I'm thinking that doing the full inch and a quarter at once is the best method (I've read that a mortar bed needs to be 1-inch thick minimum). Then once that cures, I'll set the slate in thinset.
Speaking of curing, I heard recently you should wait 28 days for your mortar bed to cure before setting the tile on top. That was a surprise to me--anybody else hear that?
if you are setting on a slab you do not need anything near the thickness you are planning -- the thickness is only to build up to match the wood floor transition. The 28 day deal is the concrete set time to reach 90% strength -- it does not have anything to do with your project- you could set it in the morning and lay the tile that evening or the next day -- so build it up with what ever is cheap (premixed is great for such a small job) and then use thinset like was mentioned before -- remember thin set
Mud is my thing. I'm a Mud Man.
I buy generic Mud called "DryPack" at most masonry suppliers. It is also called Deck Mud.
You can also make your own by mixing about 5 parts sand to 1 part porland cement. But thats a pain in the a s s.
Don't use concrete. It will shrink and crack, and be too hard. Don't use any admix either. It will make the bed too hard.
Get a masons mortar box and for 80 square feet an inch and a half you will need about 30 bags of Drypack. Each bag covers 4 square feet about an inch thick. Do the math yourself, I am guessing.
Mix the mortar about 3-4 bags at a time in the box with a Mason's hoe and very little water added incrementally and slowly. Don't use acrylic ad mix or latex additive. It makes the mix too strong. Use only enough water so when you grab a handfull and squeeze it, it forms a ball and stays together. Keep mixing and adding water slowly until it barely clumps together. They mix some more very slowly and when you can form a ball and the ball stays together, stop. It is wet enough.
This seems crazy, it will seem way to dry, and you'll have to fight the overpowering urge to add more water. You want it this dry, really. Load it into 5 gal buckets and cart it into the home.
Before you spread the stuff, have helper mix up some thinset into a slurry (a watered down version of thinset and spread it over the floor area you are going to cover with mud. Don't cover it all, just the portion that your three bags of mortar is going into. That will help the mortar bond. You could also use concrete bonding liquid, but I like a thinset slurry.
I use 3/4 conduit as screeds and set one piece in a pile of mud and get it at the same basic elevation as your matching floor and get it level front and back. Use the matching floor as one screed and the conduit for the other, and fill in between with mud. Use a straight edge to level it off. If the matching floor is carpet or hardwood floors, then you will have to use another piece of conduit, 'cause the mud has to be below the carpet, so the tile/slate ends up at the right height. You might want to use a piece of tile/slate as a guage block to set your screeds. A 6 or 8 foot level comes in handy here. Aluminum straight edges that nest come in handy here too. Buy them at a tile store.
You can add some 4x8 sheets of 16 ga. 2x2 galvinized wire if you can find it. I often use rabbit fencing at Home Depot, cut into sections and flattened. Put this no higher than about one third up from the bottom of the mud pack.
Use a wooden float to smack the mud down and compress it after striking it off. You can finish it off with a steel trowel for a smoother finish, but I wouldn't bother. A rough sandy setting bed is perfect.
Keep filling in and striking it off with a straight edge and moving the conduit down the line.
When you are finished, cover the area with kraft paper and let it sit for about a day. You can walk and tile on it the next day. It does not have to cure.
There is a misconception about mud and psi strenth. The mud is not structural. You are not driving a car over it. Foot traffic is all that it will see. You don't need 3600 psi.
What you want in a good mud bed is a nice dry sandy looking bed. If there are high or low spots (there shouldn't be 'cause it is so dry, and there won't be much evaporation to cause shrinking), they can be easily filled in or shaved with a steel trowel when you set the tile. You want a good "workable" bed.
If you added latex or acrylic ad mix or use concrete, there is no way a tile setter could work the bed in that way. Too d a m n hard.
This is my 2 cents worth.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Spasibo, Boris. Sounds like you've poured a few of these in your day.
That makes sense about the curing--actually a tilesetter pro I know told me he just "learned" that at some conference recently. Don't know if it was a trade association or some manufacturer reps who asserted the 28-day thing.
One question--when you say adding something like Acryl 60 makes the bed too "hard," what do you mean exactly? Do you mean it's impossible to shave off a bit here or there or otherwise fine tune the bed before you set the tiles? I'm just curious--seems to me it would be rock-hard after curing and that's what you'd expect and want.
By the way, how big are those bags of mix you use? 50 lb.?
28 days is how long concrete takes to cure. It's a chemical reaction thing.
no don't quote me here...but over 50% strength takes 3 days...
90% takes 7 days...
and a full 100% takes 28 days.
something real close to that.
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
You know, I take a week off to chill out, and get back on track for the people person merit badge, but it seems you gave hoser advice on the last tile thread, (not just you, you all did. Too bad you all couldn't have worked it out, it wasn't that tough).
Now mud is concrete? Ouch guy, what the hell kinda books are you reading this advice from? Stick a beer in the idiot hole, and listen to Boris.
How is the master carpenter thing going, any luck there?
I didn't tell the guy drypack take 28 days to cure...
he asked what 28 days was about....
and it's about concrete curing.
and...
backer board ain't structural...and shouldn't be counted as part of the subfloor "thickness"....
Wow..that's odd....
seems I was right on both accounts and U spedread things wrong....
weird how that happens.
Now..add that to your list of facts.....
concrete.....full cure.....28 days.
Jeff
Buck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
Are you done now?
Cbu's bonded are structual.
Concrete isn't a bed option.
Let me know when you wanna drink beer, but we'll have a prob with that too.
Jeff J. Buck
CBU's (concrete backing units?) and CMU's (concrete masonry units) are drypacked concrete.
Tile mud is drypacked sticky sand.
Add enough cement to tile mud to give a 3000# mix and you got that dry pack stuff they pack under columns and plates and it is very structural.
Just MHO, but I think that this is where you two great guys are butting heads.
SamT
U ain't trying to make me scan in the article I re-read last nite.....in an old JCL....sometime at the beginning of this year.....which covered the top ten tile mistakes.....
the one where the guy says...again....that CBU ain't structural...are ya?
Cause I don't really care what ya screw up that much.....
hang on..I'll at least get the mag with the date......just for U...
OK...Jan 2003....
page 97....."Top Five Tile Callbacks".....
I was looking up an atricle on modular homes...and just happened across that one...
Kinda made the wife wonder when I started yelling.....
"I tol' them dum sonsa beaches..."
OK...first U..now the damn scanner...
here's the last 2 paragraphs.
"Finally, backerboards are nothing more than backerboards. They provide no structural value. If the subfloor provides inadequate support, backerboard is NOT an answer.
Keep in mind that subfloor recommendations are minimums. You need adequate strength to support the tile job. If the subfloor has been open to the weather and has delaminated or swollen, you may need to replace it or add a new layer to get the strength back."
Dave Gobis, 3rd generation tile setter and executive director of the Ceramic Tile Education Foundation (CTEF) http://www.tileschool.org
So now that that's covered...what kinda beer we drinking?
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
Cbu's provide the requisite support for tile, if they are bonded to the subfloor. Read all the books you want. I'm sure your books say tiling over plywood is bad voodoo, whatever.
And we ain't drinkin no Miller, lol.
Hey...
Now them's fighting words...
High Life just happens to be THE champagne of beers!
Dammit.
Jeff.....my tiles stay put.....BuckBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
Backerboard is not intended to be structural. I won't argue it can't be made that way, but it is not a good idea. I wrote the JLC article mentioned and would be glad to answer any questions about it.
Edited 6/18/2003 8:11:30 PM ET by Dave
good article by the way.
I don't have any Q's at the moment......I can read and comprehend pretty well....
quarter...now he's another story...but he won't ask any Q's that'd help me win this little fight.....
since yer here now..set him straight about the beer too, will ya?
There's another tile thread around here somewhere....the guy has problems with the tiles popping...
one post covered all the possible wrongs.....I agree with all he said....but my first thought was simple flash over......original posted mentioned back buttering which may rule that thought out though....
take a look around and see if ya find it......I'd be curious what your opinion is.
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
The truth? I didn't want a dogfight here. You win. This is how you win...
On a thread about mud base you go into detail about concrete. Nice try, keep reading.
You wanna win by defining structual to me, and you quote a paragraph, or two?
There are no absolutes in this biz, but if that is what you need, go for it.
I've been writing my own story for 30 years, and I probably read everything you read. You spec me, and I will spec you. Wanna have a conversation, detail how a job went, it is in the freaking details...
No muss, no fuss. You love the new guidelines, and I can photo every floor I did the wrong way.
Hey, the beer I can deal with. Just make sure I drink 6 of them before you go off and tell me how to do things...be good, and keep your mind open.
Cbu bonded are not structural.
just don't try explaining that concrete takes 28 days to fully cure.....
that'll really set him off....
JeffBuck Construction Pittsburgh,PA
Fine Carpentery.....While U Waite
Oh, will you all just shoot me.
Fine, No doh, cbu's aren't structual, big yank, I never said I was making staging out of the freaking things. Bond them to t&g and tile, oh freaking no. Stand back, the damn floor is gonna blow up, lol. Hey, it won't work with 5/8 ply. It won't work in many ways. But it can work, so don't tell me it won't. Details folks. Some jobs need the superhero treatment, that is your call.
Keep it real, will you?
And you , Bucko, still going with concrete?
You know what concrete is, right?
Use your head, I know you can do it...
when you 2 are done with your little pissing match let me know and I'll buy you each a beer,
I seem to remember another tile discussion where I got involved and set straight so I probably owe you one. ....Never be afraid to try something new. Remember, amateurs built the ark, Professionals built the Titanic.
Boris,
I understand your method to be the preferred one for laying stone such as marble or travertine as it allows the installer to tamp the stones into more of a visually appealling reflective glare. Or in other words, this is how to acheive the near perfect reflection on a more polished floor.
But he's using slate and in a mudroom. Is your more accurate method necessary in this case?
in the uk thats called a floor screed.
its a real art.
most plasters ( who are the people who are supposed to do it) don't because they can't get it flat.
i do know this one guy who in his late 60's who's been doing it since he was 14.
he can get it soooooooo flat.
really flat.
so flat that you can lay laminate wood flooring without any self leveling compound.
I'm still practising
aleks
Boris,
Thanks much for the help. You must be an old tile pro! Your detailed instructions will be very helpful.
Thanks again,
Kaykon
This isn't concrete. It doesn't need to cure. This is mud, a 5-1 mix. Nevertheless it will cure, but its OK to tile on top of a one day old bed. Indeed, one measure of success in how well packed and dry a mud bed is is the sneaker test. My boss used to be able to stand on a mud bed in sneakers right after floating it and he would leave no dents or impressions. I'm 6'6" and 250 so thats not possible. But the bed gets is flatness and strength through well packed sand, not portland cement. Thats why portland is only 20% of the bed, just enough to hold the sand together. And its dry, really dry, just wet enough to allow the mud to clump. Any wetter and it will be sloppy and will shrink.
A too hard bed becomes problematic. No matter how flat you think it is, you might not have packed it tight in certain areas, and there may be highs and lows of about a sixteenth. If you use concrete or Ad-mix, the mud bed will become "too hard", and will reach psi levels of over 2500. So when the tilesetter comes back to set the tile, and sees a hump, he will either have that same hump in the floor, or has to get out the grinder.
The way I do it (no Ad-Mix) and tiling the next day, the bed is less hard (1500-1800 psi)and hasn't cured yet, so the bed is still workable. I can take that hump and shave it off by hand with a steel trowel.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Boris,
Thanks for the information. The indepth nature of your reply is very helpful.
Thanks again,
Shel
Funny, I just answered this question ten minutes ago in another thread.
Take a look at post 31807.5 and see if that'll work for you.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
Edited 6/17/2003 11:16:44 PM ET by Dinosaur
Edited 6/17/2003 11:19:24 PM ET by Dinosaur
Edited 6/17/2003 11:20:40 PM ET by Dinosaur