As a cost cutting measure we did some additional finishing work in the basement rather than have our incompetent contractor and his unsupervised crew do it. Finishing was definitely not their strong point, to put it mildly. We decided to buy more of the slate tiles we had them install in the sunroom and entry ways to put on the unfinished concrete floor in the basement. When our contractor's guys first installed the tile it looked great for about one day before it got a gray haze and just looked like a dirty mess. No amount of cleaning would help, the tile would look stellar when wet and then dry gray and boring. It drove me insane. So when we laid the new tile down we decided to actually read up on the best way to install slate tile and realized they had made a big mistake—surprise, surprise. Fortunately we were smart enough to do some research and come up with an infinitely better way to do things.
Since slate is a natural stone tile it is prone to breaking apart and capturing a lot of dust and grit in its pores. What our contractor's guys should have done is laid the tile and then cleaned and sealed it before grouting. When you grout you essentially have to spread the grout on the entire surface of the tile and then wipe it off after the grout has sets. The varied, uneven surface of slate makes washing off the grout very difficult and then all that grout in the pores is what gives you the hazy look. If they had sealed the tile before grouting it would have been much easier to clean off the grout and the rich color would have been preserved. That would have certainly been the easier way to do things. They could have even done the grout first and then cleaned the tile really well and finished it off with the sealer, but again they had no eye for finishing details and could not have cared less about doing things correctly.
To remedy this Eric and I got down on our hands and knees and did three passing of scrubbing our new slate tiles in the basement after it was set in the mortar—yes, it's that dirty naturally. Then we put one layer of the tile sealer on. When wet the tiles looked amazing: beautiful, bright and vibrant. We waited with baited breathe for the tile to dry. And when they did they still had that wet look, no more haze! Then we grouted and it was infinitely easier to wipe off the newly sealed tiles which preserved their lovely colors. We will definitely go back to do another coat of the sealer as soon we've finished all the painting in the basement, but the difference is night and day as you can see. We plan to go back and deep clean and seal the rest of the tile that was done incorrectly by the contractor in the near future, which will be much harder than it would have been if they had done it correctly in the first place. Oh well. At least we should get the same results in the end.
Here is the tile in the sunroom, which has not been thoroughly cleaned or sealed yet. See how gray and boring it is. Also see how cute Vincent is:
Same exact tile in the basement, all the tiles outside the red lines have been cleaned and sealed. There's much more of it done that you can't see in this photo. What we are showing here is that everything inside the red line yet to have the grout cleaned off of it. Big difference and this is just one coat of the sealer. It may have took hour and hours and been a real pain but we love it! 24 hours later they still look exactly the same. Yay! Next we will do another layer of the tile sealer and use a grout sealer to seal the grout. That will make the grout a slightly darker gray. After that these tiles should be good with just mopping for 3-5 years before they need another deep cleaning and sealing. Behold their majesty:

Your floor looks fantastic! We're gearing up to do exactly the same project in our home: the entry & kitchen will be natural slate tile, 12" square.
You've done a lovely job and I plan on using this as inspiration that our efforts will be well worth it in the end.
Posted by: Stephanie | May 24, 2008 at 08:16 PM
thanks Stephanie! The sealing of the tile is definitely the secret, so make sure you do that! Good luck...
Posted by: dana | May 27, 2008 at 11:33 AM
Hi...I have the exact same problem with slate i laid in my basement. could you tell me the names of the products you used to clean and seal? My problem is that we grouted before sealing and now the grout is in all the crevices. i think a wet look sealer will do the trick but not sure. Would appreciate your advice on products to use! thanks...
Posted by: Larry | February 13, 2009 at 12:39 PM
Hi Larry,
For cleaning we just used warm water, cotton rags and lots of elbow grease. For sealing the tile we used a couple of expensive wet look tile sealers that all worked, but the best by far for the price was Behr's wet look masonry and natural stone sealer from Home Depot. This was not sold in the tile section along with the fancy sealers, but next to where they sell the masonry paint. It can also be used outside. Initially we applied it by hand with rags but then we bought a paint sprayer which was MUCH faster. Hope this helps!
You can see details on how we used the Behr sealer outside here...but it also works inside
http://www.danabushman.com/here_is_the_house/2008/10/sealing-slate-s.html
Posted by: ~dana | February 13, 2009 at 01:14 PM
Wasn't this slate "make-over" on the "King of Dirt" show? That show inspired me to cover my patio in slate. I'm about 2/3 of the way done and if it comes out looking as good as yours, I will be very happy! Great tip on the BEHR sealer. I have been pondering for days how I was going to grout the tiles without getting it stuck in all of the little cracks and crevices. I will be swinging by HD on my way home to pick up a gallon.
Posted by: Mike Bisson | September 30, 2009 at 03:01 PM
yes it was...there are tons of posts about the King of Dirt show starting here
http://www.danabushman.com/here_is_the_house/2008/09/were-on-tv.html
the BEHR sealer is definitely the best. Over a year later it still looks good inside. We had to do another pass outside after the slate took a beating over the winter, but it was nice and easy and to and came out great. One bottle seems to go a long way too. Good luck with your slate!
Posted by: dana | September 30, 2009 at 04:21 PM
Got a question. I am doing my front foyer in slate tile, and so I washed and then pre-sealed all the tile with a coat of Behr wet-look sealer (mentioned above) before installing the tiles with thin-set. So far, so good. Now I am grouting the floor and damp-sponge wiping very carefully as I go to avoid film or gritty grout residue in any crevices . Here's my question: I plan to put a couple more coats of the sealer down after I finish with the grout, that way to seal both the grout and the tiles at the same time. how long should I have to wait for the grout to dry before applying this sealer?
Posted by: Milly Lyon | October 20, 2009 at 04:01 PM
Hi,
I've been reading your info, and it is very helpful. However, since you wrote all this in 2008 and it is now Oct. 2009...could you let me know how your slate tile looks after a year? I have it in my kitchen, and although we did seal it with a water-base sealer, it doesn't retain its "wet look". I really like the natural colors in the slate and want them to stand out at all times - not just when it's wet! lol (I don't really want the finished look to be too "shiny", though.) It looks good when we put the sealer on it, but when it dries, the colors are not as vibrant as when it was wet. We have had this tile on the floor for several years (which we did seal it at that time, too), and have just cleaned it and put 2 more coats of the same sealer on it in hopes that a couple more coats would help. We had the same results: it looks very clean... but... the colors don't stand out! I want to seal it with something that will keep the colors standing out before putting all the excess items back in my kitchen (as right now the floor is completely empty!). Your info on the Behr sealer sounds really good and it is so cool that you let us all know where to purchase some that is cheaper but still a good product. (I was noticing the prices on some of the sites that sell tile sealers, and it can get ridiculously expensive!) Please let me know asap how this sealer has worked for you and if it still looks as good as when you first applied it a year ago. I will probably go ahead and purchase it soon, but would still like to hear your feedback on it. Thanks so much - for your tips - and your answer, too! btw, your outdoor area looks GREAT!!! ...and your kitty cats are cute, too! :)
Posted by: Debbie | October 24, 2009 at 02:50 PM