I’m planning to install a slate floor in the foyer, hall, kitchen, powder room, and dinette in a new home and I have some questions.
- What is the difference between guaged and calibrated?
- Is slate flooring graded and what does the grading relate to (thickness, hardness/durability, appearance, etc.)?
- Are higher grades less susceptible to surface flaking, and is this important when choosing the product?
- Will sealing help to minimize surface flaking?
- Is 1/4″ Hardi-backer sufficient underlayment (3/4″ T&G fir plywood sub-floor over 2×12 joists)?
- Will slate hold up in a dinette area where chairs will be sliding back and forth?
Thanks,
Scott
Replies
I don't believe sealing will do much to prevent surface flaking. The sealers don't have any real strength, like an epoxy or anything. Most sealers are very thin liquids, porous enough to allow water vapor to escape, while blocking liquid water.
Slate is soft, and will scratch underneath dining room chairs.
There is "slate" tile i.e. ceramic tile that looks like slate that you might research too.
I've shied away from actual slate for the reason you and Wayne have outlined.
I just installed slate flooring in our kitchen and entry area so can speak from a bit of experience. I believe "gauged" means generally constant thickness, whereas "ungauged" will vary somewhat. The ungauged will flake to some degree as you mentioned. I used a type of slate in our kitchen that was referred to as "honed". I'm not sure if that is the same as gauged but it hasn't flaked yet and is a lot smoother than other types of slate.
The sealers are designed to prevent (or reduce the risk of) staining due to spills, etc. and have no structural benefit. The flaking of slate is just something that you'll have to get used to unless you use honed as I mentioned above. Assuming your floor framing is 16" on-center, you should be fine. Remember to mortar the back board right to the floor then screw it down as recommended by manufacturer.
Regarding the ceramic look alikes, I found them to be unconvincing when compared to the real thing. We did think hard about alternatives because slate being slate, will flake and could stain from spills. It is also harder to keep clean due to the variations in the surface. Oh, and grouting is a real picnic- make sure you apply grout release to the surface before starting or you'll be spending hours trying to clean the tiles off. Bottom line for us was that the benefits of using the imitators weren't enough to offset the beauty of the real thing. Good luck.
I have some sombering advice for you. I hate slate. It is usefull only on blackboards. The stuff sheds material like a long haired dog; it soaks up stains like a white suit; and it is very very high maintenance.
If pressed, the only place I would install it would be on a backsplash.
Your setting bed has to be dead flat. A mud bed is probably a necessity.
It has to be sealed every couple months.
It will still flake off and soak up stains.
Get a ceramic lookalike.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Scott -
Slate is, as you know, merely compressed layers of sedimentary material that have been bonded together through time and pressure. This bond is weak which results in the 'flaking' or cleavage of flakes off the surface. In fact, slate is actually cleft from blocks in a similar manner that shingles are split from a bolt of wood.
Since the material is weak with cleavage planes on the top, it's obviously weak on the bottom as well. Thus it requires a very, very intimate contact with the setting bed which, in my opinion should be nothing less than a full depth mud (dry-pack) conventional installation technique.
Slate is weak in punching shear as well. Guess how they make holes in slate shingles .... with a punch. Imagine person sitting on a dining room chair and rocking his/her weight onto one or two legs. All that person's weight concentrated onto the small areal of the chair leg or legs without adequate support in the setting bed and you've potentially got a hole through the slate floor. Granted slate shingles are thinner than flooring material but the potential is there none the less. You'll poke a hole in it before you'll break it in at least half the cases.
Don't get me wrong .... slate can be a beautiful floor if the quality is good (adequate density to minimize cleavage failure and punching shear) and the slate is well bedded and bonded to the setting bed. I personally would never install slate over anything less than a 1" bed of drypack mortar using portland cement as the bonding agent sprinkled heavily over the floated setting bed and painted thickly on the back of the slate tile.
I would avoid any thought of trying to use a man-made imitation of slate. If you decide to go with a man made tile instead of slate, pick something that's truely tile and not something that's trying to be something else.
Dennis in Bellevue WA
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I love slate. I will be installing some next week to make a flush entry to a basement slider on a job I just started. Ignore the doomsayers, they have no class, LOL!
I installed ¼" gauged Vermont slate under and behind my wood stove in 1995. The hearth area is subject to some fairly heavy whonks as logs get dropped on it and kindling gets split on it (you shouldn't do that, tho!), and has stood up so well you'd think it was installed yesterday. I have no flaking, no chipping, and no staining. Dirt and ash clean up is a wet mopping and a coat of acrylic floor 'wax' (Future or similar) once in a while. This installation was done with thinset over a 2" concrete pad (because of the wood stove). I had no problem whatsoever cleaning up the grout, BTW, and did not use grout release compounds.
On the wall side, I made a mistake and installed the slate on ¼" cementitious backer board screwed to metal furring strips to provide the required air space for cooling. I again used thinset. The thinset presented no problems. It's the friggin ¼" backer. The slate is heavy, and after a couple of years the weight popped a number of the screw heads through the backerboard. The board immediately re-acquired it's natural curve and the grout lines cracked and some chunks of grout fell out. Then the backerboard itself cracked. I'm going to have to rip it off and replace it one of these days. But amazingly, the slate itself is still all in good shape. No cracks at all in the slate. I could theoretically pop it off the wall, cut the backboard square to the edge of the slate pieces, and re-lay it on the proper substrate.
I would recommend minimum ½" backerboard and truss head screws. You'll have to use a trowel notched deep enough to hold the slate off the screw heads. Use tile mastic or thinset to glue the backerboard to the subfloor. If you're going on a wall, I'd cut out the gyprock and replace it with ½" plywood substrate to glue & screw the backerboard to. Or set the slate directly on the plywood and use ¾" ply alone.
If you want to use the slate in your dining room, that'll be okay but you'll need to put felt pads on the feet of all the chairs and table, and change them when they accumulate too much grit, about every year or so.
Dinosaur
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