To waterproof or not, that is the question...

[Ballymom]

I'm V_E-R-Y new to tiling and am tackling my 1st major project of laying ceramic tile in a powderroom/laundryroom/mudroom combo space. It's a new addition to our home with new subfloor (Advantech flooring). I'm using a 17 x 17 tile, 1/4" USG fiberock backerboard, 1/8" flex grout. My question is do I REALLY have to waterproof this space before tiling? I've purchased a small boat load of North American 1660 roll-on waterproofing but if it's not REALLY required for a proper job, I'm happy to skip it. If I should do it, I will but the question becomes, "Does the waterproofing compound go over the new subfloor (before backerboard) or over the newly lain backerboard?" I've received conflicting information and would greatly appreciate your expert advice! Many thanks from a Newbie Tile-Setting Mom.

[stullis]

It is not absolutely necessary for your application.
How much water is really going to end up on your floor?

What are you calling a "flex grout"?

[Ballymom]

Not much, unless my Toto toilet in the powder room decides to overflow. I'm pretty confident the washer is a safe area. There will be the occasional water from the bottoms of my 3 boys' shoes but I think that'll be minimal and quickly wicked up by a towel. The grout I'm using is North American 4200 sanded groud with polymer and North American 3240 Rapid Flex fast set thinset. Sorry, flex grout is probably the wrong term. See, I'm new but want to learn the "right" way.

[stullis]

I would pick a grout that is more maintenance free. One that won't require sealing.
Much easier to keep clean and more "waterproof".

[Ballymom]

Thanks for the tip. I'm planning to seal the grout anyway just because I have 3 boys under age 10 and dirt, lots of it, is inevitable! You definitely feel I can do away with the waterproofing, though.

[stullis]

Yes you should be able to skip the waterproofing. It would make it better but in your case probably not worth the added time and cost. I wouldn't do it in my house but then again I wouldn't use Fiberock I'd use Schluter Ditra which has a somewhat built in waterproof aspect and other benefits such as antifracture and ease of installation.

I would see if you can get some of the "grout" that they use for Snapstone tile or Duraceramic. Costs a bit more than cement based grout but worth it.
If not you should clean and reseal your grout every couple of years even though the sealer companies will try to sell you on their "X" year warranty.

[Kman]

I noticed that your thinset is "rapid set". If you've not installed tile before, you may want to exchange it for standard polymer modified thinset. Rapid set usually gives you about 30-40 minutes of "work time" before it sets up in the bucket.

When I do a job with rapid set, I usually dry fit every piece, then mix up thinset so I can quickly set the tile. With the shorter work time, it's not a product for everybody.

How many square feet is this room?

[stullis]

Good point Kman.
Rapid Set is a bad idea for people who haven't set tile before.

[Ballymom]

The total floor space is about 374 sq. feet. I was planning to mix the thinset in small batches as time is of the essence for completion of the project. I thought if I did small sections at a time, I could manage it. Do you still think it's a bad idea?

[stullis]

Yes I do. If you are doing small sections at a time it's going to take time anyway so no need to rush the setup.

I wouldn't even use it unless I absolutely needed a path for traffic

[Ballymom]

Stullis and Kman, thank you both for your input. I'm off to the tile store to exchange my thinset! I do appreciate your time and remarks.

[Kman]

Just for future reference, rapid set is good for a small bathroom, entry, etc. that you need to be able to walk on the same day. It's also good if you need to do a couple or three rows so you can get through the room the same day. Otherwise it's just a waste of money and a lot of extra work for nothing.