Flooring Tile - difference b/w modified/unmodified thinset

I'm about to embark on a tiling project and I've been reading as much as I can. There's talk about using unmodified and modified thinset for a variety of jobs, be it laying down CB, Ditra of just tiling. Can someone explain the difference bw modified and unmodified thinset and when to use each one?

thanks!

Basically, unmodified has no latex or polymer additives in it whereas modified does, thats how some genius came up with the different names. ;)

Use unmodified under CBU as it is there to fill voids rather than create a bond.

thanks very much! Things are clearer than mud now ;)

As far as the Ditra goes, use a modified thinset under the Ditra and an unmodified thinset over it when setting the tile. The latex or polymers in the thinset need to air dry to achieve maximum strength. With Ditra underneath and a ceramic or porcelain tile on top, the only way for the drying process to occur is for the moisture to evaporate through the grout joints which could take from 2 to 8 weeks. That means you cant walk on it or grout it until then. Most people wont wait that long. The unmodified thinset, also mixed with water, has different drying characteristics and actually gets its strength through water retention in the portland mix in the bag. So even though it holds the water it hardens up because of it. Go figure! Chemisty and physics were not my strong points, I'm only regurgitating what Schluter says in their Ditra handbook.

If you dont use Ditra then most of the time you will want a modified thinset under the tile, like over cement board, cement slab or BCX grade plywood.

awesome TileguyBob thanks! I could probably wait 4 weeks before grouting. Since I don't do tiles often, whats the best way to mix the thinset. Can I buy an attachment for my 1/2 drill or do I have to rent a machine?


the_dude

Buy a mixing paddle for your drill. Keep the rpms low to keep air out of the mix. Stick to about 1/2 a bag at a time and you won't need to worry about burning out the drill