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Old 07-11-2019, 07:40 PM   #31
HughM
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Can I sandwich the mortar bed in Redguard?

Help! My contractor thinks we should install Redguard as a crack membrane on the old concrete slab before doing the sloped mortar bed. Then he said we could either top the mortar bed with more Redguard for waterproofing, set the pavers with thinset, and seal the grout. OR, we can skip the top Redguard layer and just use the sealant on the grout for waterproofing. Will either of these work? Is it a problem to sandwich the mortar bed with Redguard?
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Old 07-11-2019, 10:09 PM   #32
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There is no advantage to applying the RedGard before installing the sloped mortar bed.

What is the plan for this mortar bed? Are you planning a bonded mortar bed or an un-bonded, reinforced mortar bed?

Using a sealant on the grout is not in any way a method of waterproofing. You want a direct bonded waterproofing membrane on top of your sloped mortar bed and I'd recommend a sheet-type membrane, but RedGard properly applied would work.

My opinion; worth price charged.
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Old 07-12-2019, 05:29 AM   #33
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The mortar bed is bonded. His reason for the Redguard under the bonded mortar bed is to serve as a crack suppression membrane for the cracks in our old concrete base. I realize we should have started over with a new concrete base but we didn't and this is his idea to help with what we have. Will it create any additional problems to do it his way and apply both layers? He comes in an hour and I don't know what to do!
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Old 07-12-2019, 07:55 AM   #34
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Hugh, there are no crack "suppression" membranes in the ceramic tile industry. There are crack "isolation" membranes available that are designed to prevent horizontal movement cracks in the substrate from telegraphing through the tile surface, but they do not do anything to suppress any cracking in the substrate.

In your application, especially with the surface condition we see in your photos, crack isolation is not likely to be effective even if you tried to tile directly to the concrete and I doubt the manufacturer would pretend the RedGard or similar would give any protection at all with a bonded mud bed on that surface and tile above that. Indeed, the only thing the RedGard would do in that application is ensure that any moisture that gets down past your mud and tile installation would remain there permanently, or at least until your first good freeze.

I think you'd be far better off bonding your mud directly to your concrete with a slurry of thinset mortar (a cleavage membrane and reinforced mud bed would be better) and using a good crack isolation/waterproofing membrane on top of your mud bed, flashed appropriately to the wall of the building to prevent any water getting down into the substrate package.

Good flashing, good waterproofing, and good slope away from the building are your best hope for a lasting tile installation.

My opinion; worth price charged.
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Old 07-12-2019, 07:02 PM   #35
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Thank you CX

Well always more to learn and thank you again for the valuable info! Here's another question- does anyone know of a good substitute for bond breaker tape? I want to bridge an expansion joint with Redguard and their data sheet says to cover the joint in the mortar bed with bond breaker tape, then top with Redguard. Also need to prevent 3 way adhesion at the bottom of a shallow expansion joint where backer rod won't fit. Our local stores have never heard of bond breaker tape and don't stock it.
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Old 07-12-2019, 09:12 PM   #36
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Hugh, if you Google bond breaker tape you'll find plenty of online sources.
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Old 07-13-2019, 01:55 PM   #37
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Crazy idea?

Well true confessions here. The contractor went ahead and put Redguard on the part of the concrete slab that has cracks. I stopped him from putting it on the whole thing. SO, on Monday he returns to add the sloped mortar bed, which will then also be topped with Redguard. Trapping any moisture as you pointed out. Before he returns, I am considering this idea- drilling small holes in his Redguard on my level base. For drainage. While I have a last chance. Crazy?

And the bond breaker tape- the soonest online delivery won't be for 10 days, which won't work. I read someone elsewhere who said that electrical tape will work in a pinch. Or I have some Zip acrylic flashing tape...?
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