In a previous discussion, you advised the following for tiling over a marble fireplace:

quote:

Originally posted by Tileguybob:
Rough up the marble with a belt sander then use modified thinset. You will have to build a support bridge using a ledger board (piece of very straight 1x3" pine will do) across the top for the tile to rest on while the thinset dries overnight. Otherwise they will slide. You will have to premeasure for the legs and work from the bottom up, usually the cut tile goes in at the bottom and then all full up to the row spanning across the top that was previosly supported by the ledger board.

I am a real beginner, although I have done some tiling work on a backsplash and a table. I would like to tackle my fireplace that has that common new-home cookie-cutter marble fireplace
Here are my questions: (warning: they might be dumb) -

1) What's modified thinset?
2) I don't understand the ledger board concept; you say it goes across the top....across the top of WHAT?
3) What legs are you talking about?

I'll appreciate any help you can give me.

I'm not Bob, but I know what he was talking about. When he said "the top, he was talking about the top of the fireplace opening. Here's the thing-- with thinset, the tile will slide, due to gravity. You need to use something to hold the tiles in place until they dry. That's what the ledger board will do for you. Set it up so that the top of the board is right where you want the bottom of the course going across the fireplace to be, and then tile that top portion. Once that's done and hard, you can pull the ledger board, and do the two pieces on either SIDE of the fireplace opening (also called the "legs"). As for a modified thinset, that's a thinset that's already got some kind of dry latex or acrylic polymers already added into it for strength.

Hi, Bill - thanks so much for your advice. OK, I get what the TOP is now, and also the LEGS. Seems easy now. I also understand the need to use the ledger board.
However, my confusion comes where Tileguy Bob said to work from the bottom up. In that case, why is there a need to use a ledger board?
Re: modified thinset -- I've only used mastic before as an adhesive.
1) How is thinset different?
2) How do I recognize modified thinset? Is it sold under that name or another name?
Thanks again, Bill.

quote:

Originally posted by teddymom:However, my confusion comes where Tileguy Bob said to work from the bottom up. In that case, why is there a need to use a ledger board?

Because for the major area above the fireplace opening, that IS the bottom, and if you do the legs first, it makes it much tougher to do the center portion and line it up coming across, uless you do it all as one unit. That's why it's recommended to install that area first, and then the legs on either side.

As for the thinset, it's the bagged powder. It's basically a portland cement and silica sand mix that's latex fortified and gets mixed with water. It will be labeled as either modified or fortified thinset. Depending on where you go, it'll most likely be one of three-- at Home Depot, it'll be Custom Building Products' Versabond, or at Lowes, it'll either be Laticrete's 253 thinset, or Mapei's Ultraflex II. DO NOT let them talk you into mastic or "premixed thinset", which is just mastic with sand mixed in for bulk.

quote:

Originally posted by Bill Vincent:
Because for the major area above the fireplace opening, that IS the bottom

Good heavens, Bill! I thought I understood what TOP meant. Now you're telling me that what I normally think of as TOP (northwards) is BOTTOM. I am now completely confused about your terms. Please explain ..... in very simple terms, if you don't mind.
Regarding the concept, I understand the bit about gravity and sliding tiles and the need for a ledger board, and how it would be easier to do the rows across the NORTH edge, then the LEGS, then the SOUTH edge. Now, do I have the concept right?

What Bill is saying. Build a support shelf over the top of the fireplace opening to support the row of tiles in that area. Otherwise they would simply slip and fall down. Start in the middle of this opening and work outwords and up. Once you get to the legs (each side of the fireplace opening) then work your way down towards the floor.
When laying out the tile set them on the floor as you want them to look once on the fireplace. Do any special cutting and fitting then, Once you have the layout you want and after you carefully measure to see that it properly fits. Then put the tile on the mantel.
By doing it this way you do not have to worry about the tiles sliding down on the leg sides of the fireplace front as you will be setting them quickly. Once you get to the hearth level they will be self supporting.
As far as the thinset. It comes in bags like cement. Not five gallon or one gallon pails. That stuff is not what you want as it does not dry properly for this type of project and its a mess to clean up.

quote:

Originally posted by teddymom: Now, do I have the concept right?

You got it, kid!