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I would like to know if it is ever an acceptable practice to mix or blend two diverse thinsets together, and under what circumstances one may resort to this practice (outside of desperation to finish a job in a shorter timeframe)?

Specifically, I'm interested in Laticrete 125 with Mapei Ultralite Mortar Pro, in any ratio, as this is what was done.

I commissioned my 1100 sq ft floor (on a post-tensioned concrete slab on the second floor of a condo) to be tiled with 18"x18" porcelain tiles using Laticrete 125. So far, all of the floor has been installed with 125, except it seems that in my ~70 sq ft master bathroom, the installer has diluted the Laticrete 125 with Mapei Ultralite Mortar Pro, in a ratio that appears to be 1/3 Laticrete to 2/3 Mapei, although I would say it was likely mixed a lot less scientifically than that. I believe this was done to save time, since he was unfamiliar with 125 and did not know how much coverage he would get up front, had not ordered enough 125 at the start of the job, and so he resorted to doing this without consulting his boss or me about it.

Also, it appears the trowel used in the bathroom has 1/4" notches, while the rest of the apartment was installed using a 1/2" notched trowel. My understanding is that 1/2" is recommended for use with these larger format tiles.

As an engineer, I realize that it is impossible to know for sure what any blend of products would do without proper testing, but I'm hoping there may either be someone who has experienced this before, or may know why it is either acceptable or never a good idea to do something like this, as I am not an expert, or even experienced in this area.

Thanks!

izvinite
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I'm hoping you haven't paid yet.

I don't think any manufacturer would consider this acceptable. (You could call their tech support just for laughs and see what they say.) At the end of the day, manufacturer's specifications are what matter.

So let's assume you have a sub-standard job. Off the top of my head, here's a few options:

1- tear it out and do over. (At the installer's expense.)

2- if they won't do over, on the premise that you didn't get what you paid for, pay them less. (Possibly a number approaching zero, given the risk of massive failure. If it went to court, I can't imagine that the installer would prevail.)

3- engage a different professional to fix everything and backcharge the first installer.

4- trust the installer when he insists that the job will be fine and functional. This approach requires that you actually believe you'll be able to find him in 6 months when the tiles fail.

Aloysius Defenestrate
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It is Probably be fine. As it has been five years and no reply of bad news. Both thinsets are medium bed mortars(no sag)for tiles larger than 15". Only difference is the latacrete 125 is specially made so it can be used with or without a crack/fracture guard underlayment of some sort. As long as he used an appropriate underlayment where the mapei was used. I don't think it would be an issue.

Technically, as for me.. I always use an underlayment as a crack prevention, with any type of thinset. And If I were to use the laticrete 125. I would still use with an underlayment. But on a surface that would have more of a tendancy to flex and move. Such as, on a plywood floor on second story track home or older mobile home floor.As it would just add another layer of safety to crack prevention. Although,I have also used Mapei. Im not a big fan of the stuff, but it works. It tends to have a short pot life with too much sand and not enough cement for my liking. If you need to pick the tile up and add or remove some to help level it. It doesn't like to stick back down again, and have to scrape it off and re-apply new thinset.

Smotty
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