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Discussion Starter · #1 ·
We have a large custom that we are preparing to come out of the ground with but we have run into a slight problem. I will spare yall most of the details but we are having issues with the wieght of the house/back fill vs. the soil reports. Everyone involved has their own ideas as to how to remedy the problem and they range from crazy, to a 3 month endevor, to $130k shot in the pocket; none of which are very attractive. As of now the best alternative seems to be surcharging the lot with a massive amount of fill and allowing it time to compact the soil. Its estimated that this will take about 4 wks.
Now to the question...The house has 3 very LARGE porches, all of which will have about 4' of fill in them, concrete on top of that, and then tile. This is a very heavy construction method so we are looking into other alternatives. As of now we are looking at corragated steel with light wieght concrete then tile, or stick framing and going with one of the Schluter systems. Niether option is very cost effective vs fill but the wieght savings would be significant. Also, Im just not so sure about using the Schulter system in such a large application. Anybody have any other suggestions or thoughts? Thanks much!
 

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More Info Please

At this point you haven't backfilled the 4' for the large patios?

My Geo Tech here in Vancouver suggests using Lava Rock or Pumice Rock (can't recall the exact rock but he was telling me a story of backfilling flat top decks with landscaping in hi rises) something like that where backfill and weight come into play.

On a few jobs about town I have noticed guys building forms (rebar in) and capping them then backfilling and then doing their pour in one shot so that the concrete slab sits on these piers and the weight transfers to undisturbed soil.

Maybe you could do this and backfill with a mix of native and pumice/lava rock?

As far as ditra over decking it is my goto approach. Schulter.com has all the specs online for your framing needs.

Good luck
 

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Discussion Starter · #3 ·
John, Thanks for the response. To answer your question, we havn't even blocked the porches yet. Were just trying to head the problem off asap. As far as the light wieght fill go's you are spot on, it is Pumice stone. We have not had any luck finding it native though. The only source we can find is straight from Greece, and the best price we have found is $97 per ton. Fill cost would end up around $100k for the amounts we require. Not an option. Our concrete guy suggested the forms you mention so that idea is definatly getting tossed around. Can you tell me more about your experince with Ditra? You seem to an advocate of the system. Have you ever used it on large porches? We have two that are going to measure 15'x54'. When you use it on the exterior do you follow thier prescribed methods (ie, membrane, Troba, lite wieght concrete, ditra, tile) or do you have your own way?
 

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I'M having issues with suggesting Ditra for freeze/thaw conditions. The problem lies with the recommended thinset for Ditra over concrete; non-modified. We use Mapei thinsets so that would be Kerabond. The only way Mapei will allow Kerabond in a freeze/thaw is when you mix it with Keralastic, making it modified. You see the issue?

Now, perhaps Laticrete has something that might work better, I haven't investigated. My point is I believe there are other products that are better suited for exterior applications. There is an ongoing thread about a concrete retaining wall where the OP ended up getting Laticrete TM's involved. They had 2 options which to me, seemed better than screwing around with Ditra. I know Hydro ban was one of them. Also, I believe some of Noble's membranes will allow modified thinset for installation.
 

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Exterior Grade Ditra Installs

You can install the Ditra to the new plywood decking with MODIFIED THINSET. If you use non modified it won't bite. Once you have your Ditra laid the seems need to be taped with Kerdi. This step you do with NON-MODIFIED THINSET.

We use up here in Vancouver and I'm guessing I get more cold and rain than you.

My home had it (full reno - mid point), is getting it again and we have done 3 exterior jobs in the past 5 years. No call backs.

Schluter has every spec outlined in there manual. From the size of lumber to how to fastening the decking.

The Modified - Non modified debate is one that always causes confusion.

It was described to me once like this.

The strongest concrete cure is a slow cure. If you add latex additive to the concrete you slow the cure down and make a stronger bond.

If you are using Porclean tile say over Ditra the late around the edges of the tile cures but it can never dryout in the middle. You trap moisture in the center of the tile that will freeze and cause the tile to heave in the dead of winter. Cement dries through hydration so the moisture migrates to the grout joints.

If you want a bulletproof install you can set your tile with a product from Mapei called Granny Rapid. Specs on line.

The biggest draw back to exterior tile jobs is efflorence. With Granny Rapid you get none. Buts it's pricey.

Do your reading and post your Ditra/Kerdi questions on John Bridges forum.

Good Luck. I will be laying my new deck this spring and will upload my steps one by one.


In regards to Ditra over Concrete we install it all the time indoors over our mud beds and SLC. For the best bond if you waterproof your deck with a product like RedGuard first then the non-modified you should be fine. Again Schulter has beening doing this for 20 plus years check out there manual it's almost as thick as Simpsons Strong Ties.
 

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Just a few quick items - you should get the TCNA guide - they have listed all the acceptable ways of laying tile outside, inside, etc...

Pumice - we used to get ours from Flagstaff, AZ (back when I lived in AZ - for landscaping). As I recall there was also a place in Utah that the NPS used. http://www.pumice.ca/ is in Canada & might be cheaper than importing it from Greece.
 

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Well thanks for the lesson, Dr John Whipple Schluter :laughing:.

I didn't mention Ditra for indoors apps. I was strictly talking about installing Ditra over concrete in a freeze/thaw condition. And I didn't say it wouldn't work, I said I believe there are better products for that specific application.

There is no confusion over modified or not. Schluter defines this very well. Use the appropriate thinset for the application or lose the Schluter warranty. Simple.
 

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here's another option: Dry Joist. It's a finished aluminuim deck surface.

Also, Dal Tile had a corrugated metal/mud base system shown at their summer seminar. Do you want me to try to find that system,too?
 

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Measure,
Actually it can be used with tile. You'd have to call them to get the specifics. What it would cost? That's another issue.
BTW, companies like Patio Enclosures use an aluminum skinned foam and beam system for roofs. Perhaps some some version of that system could work for you. Don't think that concrete is too compatiable with aluminum but maybe membrane the thing and go to it.
 
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