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Unread 11-25-2020, 11:12 PM   #16
wetcoaster
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I used towards the upper range of the water as per directed on the bag of Mapei, mixed it to a “semi fluid consistency, but still able to hold a notch” as Schluter instructs, applied the mortar, troweled it with the appropriate trowel, embedded the Kerdi band with a 4 inch drywall knife, squeezed out excess mortar and made damn sure there were no air pockets.

Funny, the bag of thinset says nothing about “pot life”, mixing speed or type of paddle to use. The thinset definitely wasn’t performing properly.
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Unread 11-26-2020, 01:34 AM   #17
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I know what you mean about instructions. But most folks gravitate towards the easiest-to-use products. Consider what you, yourself said about roll on membranes. But if we dug into roll on waterproofers and talked about what joints needed fabric reinforcement, the detail of each joint, the range of wet application thicknesses, using a wet film gauge to help you amend your application technique, and perm ratings for a given thickness and your needs for your type of shower.....you might not think they are so much easier.

The more you dig into anything, the more there seems there is to be worried about. Sometimes certain products truly are easier to use than others. But many times, ignorance is bliss and less instructions make more people more comfortable. The downside is exceeding the limits of a product and having to pay a price to fix it when more upfront instructions could have kept you out of trouble.

The likelihood of improving the performance of your mortar by amending how you mix your mortar is very good. If you explain your process of mixing, we’ll share what we know to achieve better results.

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Unread 11-26-2020, 01:53 PM   #18
wetcoaster
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Good day and Happy (American!) Thanksgiving,

I emailed Schluter last night after talking to you guys and received the following response this morning

“Unless you are are to remove the thinset completely off of the Kerdi Board, we would recommend to replace to cut out and replace the affected area only.
Also please take note that the Kerdi Band will not adhere to the lip ( flange ) of a bathtub with thinset mortar. You will need to use the Kerdi Fix for that area. “

My process for mixing my mortar was to fill a bucket with 6 litres of tap water, dumped in the bag of thinset while mixing (which is hard to do...lol), mixed with a drill and mixing attachment for I think the bag said 5 minutes, waited the slake time (I don’t remember what the bag said...threw it out this morning) mixed it some more for the suggested one or two minutes. I added some more water as it looked a bit thicker than the Schluter video on YouTube, mixed a bit more and then got to work.

I was honestly mostly focussed on getting it to a “fairly fluid consistency, but still able to hold a notch” as Schluter tells you over and over and over again!
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Unread 11-26-2020, 03:09 PM   #19
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Not a pro, so take these words with a grain of salt!

Jonathan, the pros will confirm but I suspect adding water after the slaking period was part of your problem. I’m using custom blend versa bond on my shower and those instructions say to mix it for five minutes, let it slake for 5 to 10 then mix it briefly once more. And not to add water after the first mix.

I do small projects so I never mix a full bag so I can’t use the full amount of water that they recommend for an entire bag. What I do is pour an inch or so of water into a 5 gallon bucket, add about a quarter of the bag, then mix it. Within the first 30 seconds it’s usually easy to tell it’s too thin by far (which is what I’m shooting for) so I’ll continue adding more bit by bit until I retrieve the consistency I’m looking for. I try very hard not to overshoot with the powder and get it too thick, but if I do then I add a little bit more water, just a bit at a time, until I get back to the consistency I’m looking for.

For me in my projects the key to mixing the thinset has been to start at a slurry level and get thicker, as opposed to being too thick and getting thinner. Much easier to start mixing very liquid and add powder and achieve the right level then it is the other direction, I think anyway.

As mentioned before this is a chemical process and chemistry can be unforgiving! LOL! But following this process I have found my pot life to be an easy 60 to 90 minutes. Good luck on your next go around! You’ll get it!
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Unread 11-26-2020, 03:33 PM   #20
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Good advice from Joe there, Jonathan. I've set a bit of tile in my time and still I've never once mixed a full bag of thinset mortar while working alone except when we (TYW) wanted to test the accuracy of the printed instructions on the bag of a particular mortar someone had complained about. Way too much mortar for someone who operates at my speed, especially when installing Kerdi or similar membranes.
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Unread 11-26-2020, 03:39 PM   #21
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I really like those suggestions, Joe. Thank you.

Somebody somewhere told me that you have to make the whole bag at once. Next go around I’ll be buying smaller bags if I find them and / or making smaller batches.
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Unread 11-26-2020, 04:16 PM   #22
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The issue with any mortar mix is that during shipping, it is possible that materials will stratify, meaning that things like the sand and cement could separate. That doesn't happen all that often, but can be critical with stuff like grout where the pigments might cause color variations if you mixed it in batches. But, that doesn't happen often, and if you're worried about it, you can dry mix the bag up first, then use what you need to only have enough before it can become unusable. What you usually notice is that the stuff becomes more plastic and doesn't spread as easily. Depending on how close to the end is that you can sometimes remix it to loosen it up a bit. Keep in mind, what's really happening then is that you're breaking apart the cement crystals that have formed, making the now cured bits smaller, similar to the sand or other aggregate (inert) stuff that was in the original mix. Once cement has cured, you cannot convert it back to active material.

When cement cures, it grows crystals whose spikes interlock, which gives it structure and strength and the ability to bond by sticking into minor crevasses in the assembly (like the minor imperfections in the tile or subsurface, or, in the case of Kerdi, around the fleece.

Without inhibitors in the cement mix, it would fire off quite quickly. Take hydraulic cement as an example...it usually cures in minutes - it has essentially no inhibitors in there to slow it down as the goal is speed.

The chemical reaction speed will vary by temperature and the amount of inhibitors in the mix. Curing cement is an exothermic reaction meaning that it gives off heat when it happens...adding heat, means it happens faster. Using really cold water when mixing and keeping the cement where it's cold could give you a bit more working time. It's important to keep the actual working temp of the assembly within range, though (usually above 50-degrees F), so you can't tile in the winter outside or unheated new construction many places.
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Unread 11-27-2020, 01:46 PM   #23
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Happy Friday thinset gurus. Half a question and half a vent session.

Why is it that thinset manufacturers can cover their bags with all types of pictures and labels and logos and warnings in three different languages but they can’t provide a simple parts by volume table for making smaller batches than a full bag? Is it just a liability thing? So they can cop out of taking responsibility when their product fails with a defense that the user didn’t make a ridiculously huge batch of thinset thus did not follow their instructions?

Would it not be simple to provide a parts by volume table of how many ounces/liters/cups/thimbles/gallons/centilitres/whatever of mortar need to be mixed with however many ounces/liters/cups/thimbles/gallons/centilitres/whatever of water? For somebody who does not work in this industry it is downright bizarre! Nobody would ever give you a pancake recipe that called for 50 pounds of flour.
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Unread 11-27-2020, 02:02 PM   #24
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LOL! I know what you mean. It would be nice, wouldn't it, for guys like us that do this only occasionally?

I'd say it boils down to the fact that there just isn't a one size fits all solution here. Every pro (probably the majority of the market) will have a slightly different preference for how thick or thin they want the thinset to be, and the thickness desired also varies from application to application, like with your (and my) Kerdi band application. That needs to be a fair amount thinner than what you want for wall tile. The pros don't need charts, they've done it a thousand times so they know when it's right just by look and feel.

CX had a line some time back that I loved that went along the lines of "Expertise comes with experience, experience comes from getting it wrong a lot." That ABSOLUTELY applies to mixing thinset.

I'll add on to what I said earlier about my process. When I start mixing and I think it's starting to get in the ballpark, I just lift the mixing head up a few inches. Is the thinset flowing off the blade? Probably too thin then. Is it holding on the blade like a rock and not moving a millimeter? Probably too thick. I'm usually looking for just a tad (or two) thinner than peanut butter. For Kerdi band, a good bit thinner than that.
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Unread 11-27-2020, 04:06 PM   #25
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I use a bathroom scale that reads out in pounds and tenths. It's fairly easy to calculate how much water goes into x pounds of thinset. Doing this, it normally takes less than 4 oz of water or a dash of thinset to get the proportions just right.

You need to be careful about judging by eye as the consistency of thinset can vary a huge amount, depending on how well it has been mixed, changing from wow that's thick, to wow, that's great once that magic time has elapsed. That's particularly true with one highly flexible thinset I used in a class that has a bunch of rubber in it. It looked like it would never work, then, magic, it became smooth and spreadable. That particular one is a specialty product that offers some sound isolation, which is why it has the rubber particles in it.

Dave Gobis can relate, as I heard this story from him a long time ago...a guy was complaining about the consistency of a thinset and contacted his manufacturer's rep. The rep came, watched as he mixed his thinset and said he'd be back. Came back with a new bag and told the guy to try this. He started mixing and stopped. The rep said keep mixing. He did. WHen finished, after trying it, he asked, what did you change? Nothing...you just mixed it according to the instructions! Depending on the thinset, some of the components need to be properly wetted, you may need to break apart any small clumps, and distribute the components evenly, and that takes time. THen, in a modified thinset, after they've become wetted, you need to mix it again so that those modifiers now totally cover all of the aggregate and cement particles to get the full functionality and texture of the material. There's a lot more science to this than people think. You don't have to be a scientist, but it's best to follow the instructions!
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Unread 11-27-2020, 04:33 PM   #26
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I have a small digital scale like you might use for shipping which wasn't very expensive and a bucket that has graduations marked on the side. Divide the weight of the bag and the recommended water by one half or one quarter or whatever portion you want. I also have a kitchen timer for timing the mixing time and the slake period.
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