ditra membrane question


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Old 04-16-08, 09:12 PM
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ditra membrane question

so we had plan on installing porcelin tile on an outdoor covered patio. we get maybe 2 freezing days a year and that is only for a few hours. The patio and house have two or three long cracks in the slab. I know it is thru the house too as we have pulled up carpets and followed it and tile above the path of this is cracked. It all appears stable in a 13 year old house but just in case it isnt .... is this a area for ditra membrane. If I understand it the purpose is to uncouple the slab from the tile so if this crack causes expansion at different rates the tile wont crack as a result? It sounds too simple and I am afraid I am not understanding this correctly. Not sure if we will DIY or hire it but want to be a little informed.
 
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Old 04-17-08, 04:10 AM
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Good morning, Gussy.

I think it is important to discover what is causing the crack and is it finished before you consider putting down ditra and tile.

It is not really a sufficient answer to say, "The concrete settled", it's important to know what caused this failure.

Concrete usually fails for one of these reasons:
A. Improper preparation: Subgrade material must be placed with sufficient volume and compacted to maintain rigidity.

B. Improper drainage: Standing water, or even moving water, produce hydraulic forces in the many hundreds of pounds per square inch.

C. Inadequate thickness & joints: Florida receives a great many heating hours. Unless your concrete patio is 4.5" thick, or thicker, and has properly placed isolation, control, and expansion joints, cracks will appear in the wrong places and be very large.

(Are you in Florida? sounds like it from your comments

Connie
 
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Old 04-17-08, 11:30 AM
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Describe the cracks. Pictures would be a big help. Are the cracks on the same plane or is one side of the crack raised? How wide are these cracks? Do they appear to be getting worse over time or have they stabilized?

How big is this slab? Is the slab sloped away from the house to properly shed water? Is the slab painted or sealed?
 
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Old 04-17-08, 02:24 PM
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Majority of all slabs have cracks, so it's not surprising.

Ditra and a good modified thinset will work fairly well.
 
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Old 04-17-08, 08:44 PM
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All the cracks, three in total if I remember, run in the same direction. Only one has any unlevelness (new word) to it and it is pretty minimal, not even sure if I could measure it but I do plan to skim coat and smooth that out. the others really look just like concrete curing problems. I dont know if I could slide a piece of paper in them if they were straight enough. One of the floors that had them I stained and just the surface tension of the paint covered them. I do still worry about them moving at different rates.
We are in the panhandle of Fla so we do run all levels of temps, more hot than cold.
the patio is 10 X 30 and does slope away from house plus is covered. The portion that gets any rain blown onto it has a crown to it that we plan on incorporating at a grout line. The surface is not stained or sealed but does have a slick surface, not brushed finish to it. That is part of the reason for tile. It is about 4 feet from a pool and slicker than snot when it is wet.
the entire house is built on a slope so there is some water at the front during our torrential downpours but it drains within minutes of the rain stopping and no long term standing water problems.
I appreciate everyones help
 
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Old 04-18-08, 08:50 AM
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Only one has any unlevelness (new word) to it and it is pretty minimal, not even sure if I could measure it
This may be a problem for you. Crack isolation membranes wont protect against vertical sheer. If you still have vertical movement going on on this crack, it will crack the tile.

the patio is 10 X 30 and does slope away from house plus is covered.
You will need a soft joint (maybe in the middle of the 30') to allow for some expansion and contraction. 30', sunlight and changes in temperature will be an issue that you will have to address. Does the slab currently have any expansion or control joints?

The surface is not stained or sealed but does have a slick surface, not brushed finish to it. That is part of the reason for tile.
What kind of tile will you be using?
 
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Old 04-20-08, 07:11 PM
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we plan on using porcelin tile, thought about slate but decided we didnt want all the flaking problems. the slab does not currently have a soft joint. Would this be only with the ditra part or do we need to do something with the tile also? I can deal with a few cracked tile in the area with vertical shear as it is in a corner away from all traffic and would be covered at all time.
thanks all for the input. this house is a diamond in the rough and we are trying to bring it up to its potential.
 
 

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