Question on Exterior Porch project [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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C&M Masonry
10-14-2006, 05:53 AM
I am getting ready to do an outside deck/porch area with tile. The deck is on the 2nd floor exterior with a cover over it and I was wondering if I am missing anything. I will list my steps below and if you see a step I am missing please let me know.

1) 2x12's on 16" center with exterior 3/4" plywood as the base/Underlayment. (Already completed by builder)
2) Install backer board
3) Install 3/4" to 1.5" pre slope sand mix bed.
4) Install Ditra over the slab
5) Lay tile

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10-14-2006, 07:30 AM
Chis, take a look at the Ditra Handbook ( There is a detail for exterior wood-framed balconies over unoccupied spaces that's close to what you've descibed.

C&M Masonry
10-31-2006, 08:03 PM
I posted a while back about a 2nd floor porch area that I am doing.

1st question is on deflection. The joists are 2x12 on 16" center length is 12' the proch area is 18' x 12'. This is a log cabin and the joist are sitting on a beam (6"x10") beam approximately 16' long on the outside of the floor area the other side is setting on a load barring wall. I have placed a mud bed (1-1/4" to a 3/4" Slope approximately 34 60# bags of sand mix) on top of the subfloor which is 3/4" plywood and then 1/4" backer board. Will the deflection be ok to lay 18" tile?

2nd question: Can I use the Versabond Fortified Thinset to set the ditra and lay the tile on top of the ditra? I know that they reccomend using a unmodified thinset but I have been unable to find it at home depot or lowes or I am just missing it somehow.

11-01-2006, 12:10 PM
we (the hubby and i) had the same question - and i guess we still do. clarification on whether to modify or not to modify would be groovy.

we are tiling an outside balcony with 12x12 porcelain - using kerdi and ditra, along with a schulter drip edge (to waterproof the thing). the area is small, aprox 6x6 feet, solid as a rock - no deflection issues. it would be a very straightforward job if it wasn't that it has to flow seamlessly into a redwood deck with out toe-tripping (but that's another discussion).

john's book says to use modified thinset when applying the ditra - but ditra says non-modified. it appears the discussion is ongoing on this (john notes the difference of opinion in his book) - could somebody give us a brief rundown on the pros and cons of modifying? if we had all the info - we could make an educated choice as to which type of a mix to use - and then the outcome would be on our heads.

btw - we used a un-modiifed thinsset to lay the ditra and the kerdi - and a "fortified" thinset by Custom Building Products (polymer modied) [that is specifically made to use with porcelain tile] to lay the tile on the schulter products.

also - what would happen if - say 'somebody's husband' did not heed the warning and mixed the 2 products (not in the bucket - just used some of the modified under the ditra/kerdi alongside some of the unmodidied). would it be the end of life as we've come to know it?

so ... i wait - prepared to wince when you tell me i've done it wrong. be gentle with me.

we have a fair bit of the modified thinset on hand- as it's recommended for use over radiant heating systems, and we've got about 700 sq feet of warmboard & pex inside the new mstr bdrm we are going to cover with ditra and tile in a few weeks.

modify - or not? modifiy it myself with an acrylic additive - or trust the already "fortified stuff at the Depot?


John Bridge
11-01-2006, 07:48 PM
The big question I have is how did you waterproof the installation? Also, you've got backer board under your mud bed?

Jacquie, you'll need to make your own thread. We will never be able to keep up with two projects here. :)

C&M Masonry
11-01-2006, 09:00 PM
John I am using ditra as my waterproofing membrane on top of the mud bed. Yes I placed 1/4" Hardi-backer over the plywood subfloor to give the mud bed something to grip to.

Also this is a covered porch area in which water will only get on it if the rain is blowing.

11-01-2006, 09:33 PM
I combined your origional thread here, Chris, thinking we'd get some more info, but looks like Injineer Bob just pointed you to the TCA Handbook methods. You ever take a look at that?

And I don't see indication whether this is over occupied or unoccupied space.

That tapered mud bed isn't a real good idea in my opinion. The place you're supposed to create your slope in these deck installations is in the framing. That way you can have a mud bed of a consistant thickness and still have the proper slope. As it is, any moisture you get in that mud bed (you're outside, you'll get moisture in there) will just hafta soak down into the wood decking eventually, which I would consider a problem. And with only a half-inch of slope in twelve feet, your water isn't gonna run off the surface all that readily, either.

But you've got what you've got.

I think most codes require your deck to be calculated with a 60-pound live load. And you've already got something in the neighborhood of 12 psf dead load plus your tile installaton. I think your joist structure is up to the task, but I am somewhat concerned about that unsupported beam across the front. I'm not equipped to calculate that, however, and best we can tell our resident Injineer is off cavorting in the islands or some such. He usually returns eventually, though.

Keep in mind also, that the most common place at which raised balconies fail is at the attachment to the house. Fella wants to be very sure of that part of the construction so's he don't have the upstairs gaggle of people at the big party become one with the downstairs gaggle. This usually causes the party goers to become ill content and much blame is frequently cast about.

But if y'all have already done what you're fixin' to do on that deck, you might as well tile it, seems like. But I really would like to see a calculation on that front support beam. Who did the initial design of the deck and was it calculated with the tile installation in mind?

My opinion; worth price charged.

Steve in PA
11-01-2006, 10:14 PM
I just took a picture of the one I’m working on today…

notice the kerdi band along the walls and seems for waterproofing.