Standard for Uncoupling Membranes

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JohnfrWhipple

BATHROOM DESIGN & BUILD
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What causes Hair Line Cracks when an uncoupling membrane was used?

Case Study #1

"...I had a near same situation cept mine was 2x10`s 16 OC 11.25 max unsupported ,3/4 T&G/ I re-screwed to assure proper fastening then 1/2"second layer ply,set as described here below Using 1 1/8 screws every 3-4 inches on seams and 4-6 in field

http://www.johnbridge.com/images/mik...-0604.pdf..pdf

Ditra attached to ply with Lat 254, all base and cabinet base removed ,sill seal around complete perimiter, Dilex at hall/Kitchen/Kitchen Dinning rm,and Living rm (Hardwood) all 12x12 tiles back buttered then 1/4/3/8 trowell used to set tile then grouted with Mapei Ultra color , 450 sq ft tile.
6-8 weeks later .............Fine hairline cracks and mainly over the second layer of ply. Schluter came out and I tore up 3 tiles to provide adequate proof of proper install and took pics as needed .

Bar bringing in a structural engineer Schluter had no reason for cracked grout and balance of bag sent to Mapei then deemed well in date .
So Schluter asked me for a quote to replace all grout and I did they accepted and I angle ground/diamond blade all grout out then replaced with StarQuartz Urethane (slightly flexable) less prone to crack. and its been 5-7 years since with no issues.
So some things just CAN`T be splained !!!!!!!!!.....


Source: http://www.johnbridge.com/vbulletin/showpost.php?p=1381449&postcount=11


Reading the discussion (link above) it seems like three JB members have all had hairline cracking with grout over uncoupling membranes. Why?

Read between the lines. What did you learn?

1). Schluter rep asked for a few tiles to be pulled up to check coverage. Smart. I would have done the same.
2). The date of the thin-set was checked. ALWAYS CHECK YOUR DATE CODES
3). Schluter paid for the repair. Nice - that's a solid.

Case Study #2

"....Im newby here to the forums. I only have a few spots throughout the installation that are cracking. Nothing consistent. I used tec sanded grout and is on a double layer floor. First layer is 3/4" t&g ply and second is a 5/8" osb with exposure 1 rating up. (as specified from shulter tech support.) THere is perimeter spacing and is laid on ditra. The floor joists are trusses which are on 19.2 spacing and biggest span now is 12 feet. Before installation we installed beams cause joists were spanned way too far. Poorly constructed home. The home is nearly 35 years old from best guess of talking to people in the community. It has been a year and cracking seams to be the same just hairline cracks and hairline seperations from the tile. The customer wants to rip up the floor. I feel this is a drastic move and is unnesscesry. Any tips beside regrouting the entire floor. Which is less drastic than ripping up great looking floor...."

Source: http://www.johnbridge.com/vbulletin/showpost.php?p=1163741&postcount=2


Reading Between the Lines

Why was the second layer of plywood specified by Schluter Technical Support?

What I think:

I think that the hairline cracks could be anything. And for them to show so slight I would personally suspect a poor grout prep job. Or too much water when prepping for grout. Or no grout prep. The edges of tile need to be clean. Free from thin-set, dust and water.

I do not think any uncoupling membrane should be used as a substrate improvement in deflection or rigidity. Case Study #2 assumes that Schluter specified two layers of plywood. This by itself is a tile ready substrate. If a floor is moving. Setting some
plastic down over it will not help you.



 
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