I’ve got a client who needs to set floor tile on a slab. The first problem is that the slab is pretty badly cracked and should probably be slip sheeted everywhere. That would be well and good except there a sunken tub was removed from one room and the floor is about 1/2″ higher than the rest and extremely rough.
The alternatives:
1. Grind the high part and then slip sheet the whole floor. The concrete is about 20 years old and is probably extremely hard. Grinding would be a mess and expensive.
2. Resurface the entire floor. I know that there are some new concrete repair products on the market, but I have never used any of them. If we take this route would it eliminate the need to slip sheet the entire floor?
3. (This is what I’m inclined to do at the moment.) Cover the floor with backer board set in thinset everywhere but the bad part. Resurface the bad part. Would the backer board then need any joint treatment other than the usual mesh tape with thinset?
Any other ideas?
Replies
Howdy Mike!
What is a slip sheet?
This is what I would do.
1. Quick and Dirty Method. Buy Laticrete Blue 92 Anti-Fracture membrane and apply and Self Leveling Compound like Custom Building Products LevelQuick, and tile away. Make it about 5/8" thick so it evens out the whole magilla. SLC is expensive but easy to use and fairly forgiving. Blue 92 is fairly pricey, too.
2. Mud. Apply some 6 mil poly to the slab and float about a 2" thick layer of mud with some 2x2 galvinized wire in the float. You will have to make some screeds to level it, and strike off the float with a straight edge. Mud is cheap. $5 a bag, but does take some skill to do right. It is not self leveling.
I think No. 2 is the best approach if you have the necessary skills to float a mud floor.
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1927
I agree with everything Boris said, but wanted to add a few things. First, most backerboard manufacturers state that their products are not compatible with concrete slabs, i.e. that they must be screwed into a wood substrate. So I do not think this is a viable option.
Before going any further, do you have any indication as to what the cause of the cracking is? Do you know whether the cause has been stabilized (i.e. initial settling) ? Cracks that are the result of seasonal movement or improper curing time and do not result in height differences may be contained by a crack isolation membrane if they are less than 1/8" wide (subject to the membrane manufacturer's specs). If the cracks do result in height differences, this is most likely the result of structural issues, and a membrane or self-leveling compound most likely will not keep these cracks from telegraphing through to the tile.
There may be some new products out there that can help in this situation, but make sure to follow the manufacturer's specs to the letter, and do not offer any guarantee to the customer that is not backed up by the manufacturer. However, in general, slabs that are in rough shape and badly cracked do not make a good substrate for tile, as it is very hard to ensure that the cracking will not telegraph into the tile. Because of this, if you decide to go forward, if I were you I would not offer any guarantee or warranty on this job, no matter what route you choose to take.
Good luck!
-Andy