If you have a solid base on the tile below and there is no height issue there is absolutely no reason you can't tile over it. If the old tile has cracks, or if the floor shows any flex at all you should start fresh. Putting old on top of new is often done in many applications of home improvement. I just finished tiling over tile on my bathroom where the first layer was firmly tiled to my cement slab. It came out wonderful. My toilet flange happened to be elevated to the point that my second layer of tile is at a better level than the initial layer for seating the toilet. Picture is of this bathroom with the tile going in. The bathroom I did last summer had cracked tiles and appeared to flex a little, I took off all the old tile and the cement bed, added a layer of plywood to the subfloor and backerboard and retiled. Again, it just depends on what you are working with.

http://www.tile-shop.com/product_pages/porcelain_index_1.html Mirage Slate is a rectified through-body porcelain that is appropriate for residential and commercial use. The wide range of color variation imparts a slate feel, yet the rectified edge and slight texture give it a contemporary flair. It is important to blend tiles within each carton, and from different cartons during installation to insure a proper range of variation. http://www.fcimag.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000238555 A rectified tile is defined as a tile that has had all edges mechanically finished to achieve a more precise facial dimension. Rectified tile is ever increasing in popularity. Most popular are the larger size formats often used in conjunction with smaller modular sizes to create patterns. Rectified tile is also selected for its ability to allow tighter grout joint spacing. From a homeowner or other end user perspective this seems a very desirable product attribute, one they are willing to pay a little extra for. In the sales and selection process what often fails to get any consideration, and therefore no additional compensation, is the increased challenge that the installer faces in achieving those goals. Large tile combined with minimal grout joints creates a host of installation issues and this article both explores and explains some forthcoming changes as well as challenges in achieving an aesthetically pleasing and correctly installed rectified tile product. Some parts of this article are going to be a little rougher reading than most. As you will see, with the proliferation of tile types, sizes and tolerances, the tile professional will be soon be using their calculator for more than totaling up a sale or estimate. First lets explore just what is "rectified tile." Currently, it is whatever the manufacturer wants it to be! I have heard numerous descriptions of what constitutes rectified. There are no current standards to address this product category, however help is on the horizon. Ceramic tile (porcelain tile is a ceramic tile) is a product that shrinks to size as it is made. This is true for all types of ceramic products. A rectified tile is made by either sawing or grinding tile that has already been fired to a specific size, thus allowing minimal size variation between pieces. How minimal is currently up to the manufacturer; I have heard variations of .50 %, .039 %, and .025 % used for rectified tile. Normal non-rectified porcelain tile can have a variation of up to 1.5% under current standards regardless of size. There are proposed standards that have been balloted and will likely be soon adopted under ANSI A-137.1, the American National Standards for Ceramic Tile. This revised standard provides new definitions and will set a specific range of variation that a tile must fall within to be considered either calibrated or rectified based on size. The new tolerance range for regular calibrated porcelain tile will be + or - .5% up to a maximum of .08 inches based on size. For the first time a separate standard will be published for Rectified tile which limits the range of variation to + or - .25 up to a maximum of .03 inches. Elsewhere in this article is a partial chart (Table 1) showing what the allowable variations will be for a rectified porcelain tile compared to normal calibrated or non-rectified tile. Under this new standard there is also a specific definition for rectified tile that alludes to the edges being mechanically finished as opposed to pressed. Standards are about setting basic performance guidelines so all may compete fairly. The new product standard, when published, will be a great improvement for everyone in the industry. It will provide clarity that is not currently available. Now letÂs move forward to the installation side of the equation and address some challenges faced by the installer. While customers are seemingly willing to part with an extra $.50 to 1.00 for tightly sized tile product, little if any financial consideration is given to the installation. First, letÂs talk about the much sought after small grout joint. One recent ad I saw says "do away with grout joints, use only rectified tile." Another is not quite so brash and says 1/16" grout joint recommended. These are all things consumers want to hear and the marketing departments are more than willing to tell them. However, such statements make technical services departments and installers shudder because they are very difficult if not impossible goals to achieve. Let us look at the first statement, 1/16" grout joint recommended. If the manufacturer were to use the allowable variation under the soon to be published standard for a rectified 12"x12" tile, the maximum allowable variation would be .06 inches. A grout joint of 1/16" equals .0625. in essence at .0025 inches, there could well be no grout joint! Some manufacturers may be able to produce at levels 50-75% tighter than this, but at .0025 you still see the problem. The standards committee, being composed of both manufacturers and labor looked at this and decided the time had come for specific grout joint recommendations. Until recently it was understood but not written, that a grout joint width 3 times the actual average variation of the tile was a prudent recommendation. With new standards addressing and adding tighter tolerances to tile products coupled with the desire for ever tighter grout joints, the labor side of the standards committee has suggested that a recommended joint width of 3 times actual variation be adopted in the installation standards, ANSI A-108 (The American National Standards for Ceramic Tile Installation) along with the newly revised tile product standard. This proposal will be introduced in spring of 2008 and passage is expected. Seeing a use for those calculators now? Bottom line, whether calibrated (normal) tile or rectified tile, grout joints must allow for the natural variation in tile products. Another consideration that receives little thought but can cause the appearance of poor workmanship is tile warpage. All tile has some amount of warpage. It is not considered a defect unless excessive. The chart elsewhere in this article (Table 1) also shows at what point warpage is considered excessive. In modular patterns this variation can become very apparent. The issue is probably at its worst when using a larger formats in a staggered pattern, either calibrated or rectified. If the tile is manufactured as a 12"x 24" the lowest amount of warpage will be on the 12" side of the tile, the highest on the 24" side of the tile. When installing this size tile in a running bond pattern the lowest point of warpage is placed right in the middle of the adjoining tile which is at the highest point of warpage. The best installer and the best substrate can not change the fact that all tile has a certain amount of surface variation as part of the firing process. Warpage will also be less in smaller size tile when multiple sizes are used in a modular pattern. The bigger tile gets, the more apparent this naturally occurring part of the manufacturing process becomes. Last but not least on the list of challenges with rectified tile installation comes "normal" substrate tolerances. It would be an accurate statement to say anything over 12" in size is not going to have an adequately flat substrate to facilitate tight joints unless tighter tolerances are specifically requested. Normal substrate tolerances seldom seen even when specified call for maximum surface variation on flatness of no more than a 1/4" in 10Â, nor more than a 1/16" variation in 12". In new construction, this is the job of substrate trades and covered in their industry documents and recommendations. In existing or remodeled applications this tolerance recommendation typically falls to the tile or flooring contractor. Elsewhere in this article there is a picture of a 12"x24" tile with a 1/16" drill placed under the center representing a 1/16" variation in a 12" area. That small amount of variation caused a 1/8" displacement in one tile! That 1/8" becomes 1/4" in the next tile and 3/8" in the following after only 6Â of area. Large tile with normal grout joints requires a very flat floor in more than likely the 1/8" in 10Â range, not at all typical of the normal construction process. Large rectified tile requires what is known as a "super flat," which is well beyond the equipment and ability of most in the substrate trades. This leaves the job to the flooring professional that has the knowledge, skill, and products available to him. The time to flatten the floor is prior to the installation. Using a medium bed mortar may allow for minimal build-up providing a minor degree of flattening but that would be an adequate measure in only the smallest of installation areas. All this goes to say that if you are planning on doing big tile it would be prudent to figure some floor prep. If you are using big or rectified tile with small joints you should plan on a lot of floor prep. The final word: as large rectified tile gains in popularity, particularly in modular patterns, the need grows to educate the end user, sales personnel, and installers about the properties and limitations of both the product and installation. The requirements to provide satisfactory installations of rectified tile with tight grout joints are exacting and not inexpensive. The substrate flatness required for narrow grout joints is well beyond reach of the typical mason or carpenter. Unless all appropriate parties are properly educated about the product and installation needs of large rectified tile and narrow grout joints, great resistance can be expected in getting the appropriate compensation for the additional substrate work which is inevitable. Dave Gobis dave@tileschool.org David M. Gobis CTC CSI, a third-generation tile setter, is the Executive Director of the Ceramic Tile Education Foundation. Mr. Gobis is an Author of many trade related articles and a frequent speaker at industry events.

From an old GW thread with GWA (our favorite girl with aspirin and great taste) o rectified tile and grout joints... am I asking too much? Brought to you by Advertisement clip this post email this post what is this? see most clipped and recent clippings PrintPage Posted by girlwithaspirin (My Page) on Wed, Aug 9, 06 at 14:53 I'm going with semi-polished, rectified 18"x18" porcelain. The tile sales rep warned me that few contractors will be willing to do a 1/16" grout joint, but she told me to stand my ground. Sure enough, I'm gathering bids, and the first two contractors won't do a 1/16" joint. I told them the tile is rectified. One guy actually asked, "What do you mean by that?" Disturbing, no? I explained it. Five minutes later, he tried to explain to me that porcelain tiles are rarely exactly the same size or completely square. Once again, I explained what "rectified" means, wishing I could just snap my fingers and make him disappear. Both of them have given me all the reasons why a 1/16" grout joint is impossible. My house is old, the floor can't possibly be completely level, a new subfloor won't fix anything, etc. The thing is, the current ceramic is at least 15 years old, and there's not a single crack, not even in the grout lines. Am I asking the impossible? (Bill V., if you're reading this, your reco is on vacation -- I'm hoping he's my salvation!) Aesthetically, I love the look of a tiny grout line, especially with this sort of tile. Follow-Up Postings: o RE: rectified tile and grout joints... am I asking too much? Brought to you by Advertisement clip this post email this post what is this? see most clipped and recent clippings PrintPage * Posted by floorman67 (My Page) on Wed, Aug 9, 06 at 16:51 I have never heard the term rectified tile and I have been a licensed and certified installation mechanic for 27 years, so no, it isn't disturbing at all ... I have heard the term, Dimensionally Stable Tile though. two occurrances can prevent successful 1/16" grout joints. one being nominal tile sizing (tiles not exactly the same dimension as every other tile), and two being the existing floors height variances that would cause a run-off. When attempting to install a 1/16" grout joint with either present can cause tile stepping and run off becasue there is basically no joint to make it up in the installation grid system layed out prior to install. TO answer your question, no, it is impossible. However, the above considerations play an important role in it's success. Since you house is older and admittedly not perfect, you want to research and find an installation professional comfortable with this, and expect to pay a handsome fee because basically they will be either installing a mud bed, or mudding the tiles in over a backer unit (a hybrid technique), which it time consuming and not a well known technique to every ceramic installer, especially those who only do thinset/backer board installations. Many refuse to do it becasue of tile nominal sizing, extra time involved, the difficulty factors, and the lack of knowledge to pull it off successfully. This doesnt mean they are bad installers. On the contrary it means they care enough to admit they can't do it, so they refuse to do it. and them some jsut do not know the difference and think it cant be done successfully, but still install great projects all the time. I would keep searching until you find a installation mechanic who can do it. The key is the tiles dimensions from tile to tile. If they are the exact same with no variance, then it can be done. o RE: rectified tile and grout joints... am I asking too much? Brought to you by Advertisement clip this post email this post what is this? see most clipped and recent clippings PrintPage * Posted by bill_vincent (billvincent@hotmail.com) on Wed, Aug 9, 06 at 22:19 I would not install rectified porcelain, even large format rectified porcelain, any other way than with a tight 1/16" joint. That said, there's atleast one installer in my area who, in every other way, is one of the best in the area, and he won't do it, either-- not even with 12x12 rectified porcelain or natural stone-- says it can't be done, in spite of the pics I've shown him of my work. I agree with the salesperson-- don't give up. Stick to your guns. Floorman-- the biggest way that rectified differs from other porcelain (or other tiles, for that matter) is that while all other tile, porcelain or otherwise, are stamped out to size before going into the kiln, rectified porcelain goes into the kiln in sheets, and then is cut to size afterward. If you ever see it, it'll have the same exact edge as polished stone tile, with the cutting ridges and the chamfered edge. This is why no matter what the size of the tile, it can be set tight, because the tolerances are alot stricter than they are for other tiles. You'll see less variation in size with rectified porcelain than you will even with polished stone. o RE: rectified tile and grout joints... am I asking too much? Brought to you by Advertisement clip this post email this post what is this? see most clipped and recent clippings PrintPage * Posted by girlwithaspirin (My Page) on Wed, Aug 9, 06 at 23:07 Whew. Thanks to both of you. Part of me thought I was being silly. You know, what's a couple sixteenths of an inch? But the joints on my kitchen ceramic are 3/16", and on my honed limestone, they're 2/16" -- and there's a huge aesthetic difference between those two. The 1/16" grout lines I've seen with rectified tile absolutely make the look, in my opinion. I'll stick to my guns. I think I need to shift my focus and make sure I'm calling in natural stone installers.

Emma - we've done a number of tile jobs DIY with good results; however, not 13 x 39. That's a whole 'nother creature we were not prepared to tackle, especially on a vertical surface. We used that size tile on our fireplace and these two craftsmen spent most of the day getting it right. I think this large a format is too big for a backsplash. We do live in the Bay Area (Marin) and would be happy to share the guys who did this.