[Bud Cline]

Patch the drywall with joint compound, prime it with a paint primer, go again with the slate using modified thinset mortar. In this case you should be just fine.

 

[Bud Cline]

In this case you will have a lot of surface patching if you use joint compound to fill and repair the damaged drywall. That's the way I would do it and that won't hurt anything but thinset doesn't like to stick to raw drywall patch material to well so I would suggest you first seal the patching with paint primer. Let that dry over night then use modified thinset mortar for the tile. Modified thinset mortar is the thinset mortar that will have additives already mixed in the bag for you as opposed to unmodified or dryset mortar. Thinset mortars come basically two ways; modified and unmodified. It should be fairly clear on the bag.

 

[Bud Cline]

I should also caution you that thinset will not stick to the metal face components of the fireplace very well. Technically you can't use thinset on metal surfaces. But again, and in this case, you'll be OK if you do what was done previously and have enough tile attached (with thinset) to the wallboard to hold the tile. This will allow you to at the same time overlap the metal surfaces and it will work. Use thinset on the metal as was done before but it won't be dependable forever. Won't matter tho.

 

[Bud Cline]

Hey the "patch job" looks pretty good!

The fact that the fireplace ("can") isn't flush with the wall surface is an all-too-frequent problem. There's a couple of things you can do.

The first thing I would try is to move the can. If you can find the screws that hold the fireplace in place take them out and bump the can backward into the wall. There should be flex-enough in the gas supply to do this. Unfortunately bumping the can isn't always possible.

The next possibility would be to add a piece (pieces) of 1/4" cement board to the wall. This will reverse the error but this time in your favor. If you do this I would recommend using Hardibacker. Find the studs in the wall and screw the Hardi to the studs everywhere you can. This will also create a 1/4" edge around the outer edges to deal with but that is caulk-able.

The problem with just using more joint compound to fill with is that you will undoubtedly create a sloping wall surface and that's not a good thing. That would cause serious lippage at the corners. I wouldn't do it that way.

One more fix would be to use masking tape and apply it to the wall where the old line is. Place the tape on the painted wall surface to the left of the firebox. Then, use modified thinset and a 1/4" X 1/4" notched thinset trowel to apply thinset to the now filled/repaired surface. Be sure to prime the joint compound first as discussed earlier. After your combed out pull the masking tape off for a good straight edge on that side. Comb out some nice straight ridges and grooves then leave it sit over night. The next day you can use sandpaper and a wood sanding block to sand the combed thinset down to the required thickness. Don't sand too much so as to create a taper back to the wall surface.

Now you have a good solid 1/8" fill. One more time, apply more thinset to the sanded surface, this time using the flat side of the trowel. This will fill the ridges you created the first time around. Now you are ready for tile. The surface is flush and the standoff you have create is caulk-able. Now your tiles should easily overlap the can and be straight and flat.

That picture is a huge benefit for sure.

As you can see...moving the can could easily be the lessor of the evils.

 

[Bud Cline]

Did you comb ridges into the thinset on the first coat? I can't tell from the picture.

 

[Bud Cline]

Exactly correct. By building ridges and then sanding them it is much much easier to sand and get to the desired size (build out) when you only have the ridges to deal with. Thinset will sand easily if you do it in the first couple of days after application. Then-n-n-n-n-n, fill the low spots and you're ready to go.

This is also a good technique when attempting to use thinner decorative tiles with thicker field tiles. I apply the thinset to the backs of the tiles in that case one day, then sand them the next day and install them in more fresh thinset.

 

[Bud Cline]

PERFECT! Looks good!

There's nothing wrong with that!

Tomorrow sand the tops of the ridges flat and
on-plane" with the proud metal surfaces, don't get over zealous with the sanding. The bigger the sanding block the better. Filling the grooves with thinset will be much easier.

THEN...
When the time comes to install the tile and you are spreading (combing) that thinset try to spread it all in one direction. Doesn't matter which way you go. The purpose for that is so that the high spots will collapse into the low spots when you place (squish) the tile and will result in almost a 100% coverage of thinset-to-tile-to-substrate. 100% coverage is your target, 85% is acceptable. In reality you'll probably get about 95% coverage. Don't anguish over it!

Another little tip.
Immediately prior to spreading the thinset for the tile application, use a wet sponge to wipe the substrate and the tile-backs thereby removing any sanding or transit dust and introducing some moisture into the substrate. This will give you a better bond and slow the leaching of the moisture from the fresh thinset into the substrate. In fact, I always have a bucket of water and sponge at my side to keep things clean and to moisturize the cementitious substrates.

Whoops almost forgot a critical move. You will have to install a temporary lentil/ledger across the top of the firebox to support the top (horizontal) tile row until the thinset seizes the tiles. You can use anything for a straightedge that can be screwed into the framing behind the drywall.

Don't forget you'll need spacers to stack the rest of the tiles tiles. The tiles won't stay in place on their own.

You will also note that the tiles probably won't come out even as far as spacing across the top of the firebox. I would determine where I wanted the leg-tiles to stack up then place the top row tiles one left one right one left one right to match the leg stacking, and finally cut the center tile to fit whatever space you have available.

Fireplaces are generally tiled from the top down in a case such as this.

WOW, that got longer than I expected it would.

 

[Bud Cline]

So from the sounds of it, i'll need to stall a temporary ledger after every row?

No just the top row. After those tiles are firm and you can remove the ledger you can then do the math so that you stack the legs up from the floor on spacers but cut the bottom tile. It looks better and isn't as noticeable if you cut the bottom tile.

Yow I know: Clear as mud!

 

[Bud Cline]

My hand cramped so excuse the penmanship!

Here's something like what I think I would do with this one. The keystone tops are really classy looking I think, and it breaks up the hum-drum of the square tile a little.

 

[Bud Cline]

The final pass of thinset should be dry by now, it should only take a few hours. It doesn't have to be completely dry anyway especially if you backbutter the tiles.

I assume you'll attach a temporary straightedge to rest the top row of tile on. If you use the keystone idea, layout the tile for the keystone and cut it first. Then you can layout a string of tiles for the top row and use the keystone itself to pattern the angled cuts of the to-be-angled-tiles on either side. Be sure to allow for the grout line.

A 4" grinder should work fine. Hopefully you have a "dry-cut" diamond blade. A little trick there is to layout your cut then use a piece of board for a saw guide. Lay the board it your mark and allow the blade to glide along the side of the board. All you need is two or three passes then you can remove the board and free-hand the rest of the cut to go through the tile. The saw blade will easily follow the cut (kerf) you have made with the board-guide.

When using slate you won't have to worry too much about chipping the edges. Oh sure, the edges are going to chip but it only enhances the look of the slate. If the chips are too obvious compared to the edges of the other tiles you haven't cut then use some of that 80 grit sandpaper on a sanding block and soften all the edges of all the tiles to match everything up a little. Slate is one of the softer rocks when it comes to cutting like this and it's real easy to work with.

All of these tiles where cut to size. The edges where then rubbed with abrasive. Can you find the butterfly and the hummingbird?

 

[Bud Cline]

Nothin' wrong with that! No matter what you do for a pattern it's gonna look good with slate.

 

[Bud Cline]

The hummingbird is hard to see if you don't know it's there.

 

[Bud Cline]

The suggestion in the top picture would be my choice. This would maintain the horizontal grout line at the base of the firebox as long as the tiles aren't blocking an access panel on the fireplace.

To further cloud the project now that I see the tiles in place, I think I would get a little "artsy fartsy" and cut the two bottom rows narrow so that there is a vertical format appearance, a soldier course if you will. By "narrow" I'm saying to cut each of those remaining tiles approximayely the same width as the three at the top of the firebox. This would probably give you about nine tiles left to right.

There are no rules you know?

 

[Bud Cline]

EUREKA!!!

That looks really good actually.

The slate may want more than one coat of sealer. Also be sure the sealer is totally dry before applying the grout.

One more suggestion:
If you have a pastry bag (cake decorator) I would "bag" the grout joints. This will reduce the amount of grout you have to smear over the surface of the tile. With plenty of sealer you'll be OK but still, if you don't have to get too much grout on the surface of the tile you'll be ahead of the game.

Excellent job!

 

[Bud Cline]

Stone tiles such as slate (believe it or not) will absorb moisture. In this case the moisture from the thinset will wick into the back of the stone. The stone needs to be able to dry and evaporate the moisture within. Sealing this soon may not be the best idea. The sealer may turn white from the moisture and you don't want that to happen. If you have a fan I'd put a fan on it overnight.

Fortunately of all the stones used for tile, slate would be one of the least of the absorbent stones I think. No need to get in a big hurry now!

 

[Bud Cline]

If by "quality" you are referring to density and density equates with quality, and a higher density stone is considered to be a higher quality stone then...this is true I suppose.:yes: Stone densities can vary within stone categories.

All stones can vary in density and can have varied absorption abilities.

Not all stone sealers are created equal.

I have seen both granite and marble tiles take weeks to dry out with the only source of moisture being from the thinset used to install them.

Porcelain on the other hand is man made and does have a controlled and predictable absorption rate of 0.5% or less.

 

[Bud Cline]

I'm not sure porosity is a determining factor. For example; lava rock is of super high porosity and yet has a high density also. I'm not an expert, just know what I've picked up in the industry through the years.

Marbles that are highly fissured also (as you have found out) have a high mortality rate when they are in the form of a tile. I have seen marble tiles that couldn't be lifted from the box they came in with one hand or they would break. It takes two hands at all times to handle those suckers. Those are also the stones that when wet seem to soften even more and break very easily. They are also very annoying when being cut with a wet saw. In some cases when buying such stones one would have to order 50% more than really needed just to have enough to complete a given job.

The standard practice is to never seal the back of stone floor tile for the reason you mention. Actually that's a very good question.

 

[Bud Cline]

Looks pretty good from here! Nice job.