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Unread 11-20-2021, 10:49 PM   #16
JayTee
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Didn't want to sound like a Laticrete commercial. I'm using Multi-Max Lite to set the tiles and was going to use it for the Stratamat too.

You mentioned using a decoupler and waterproofing. In my research on the internet I came across some people who used Stratamat and then put a fill layer of thinset on top of it followed by Hydroban before using thinset again to set the tile. I mentioned this to the Laticrete tech person and he said you shouldnt do that and if you want to put Hydroban across the room, you should put in the underlayment wood, not on top of the Stratamat. I have no idea whats best as I've never used any of these products yet.

Will the use of Stratamat help at all in uneven floors? My floor is very flat but not level which I'm not too concerned with other than immediately beneath the shower pan.

Thanks again.

JT
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Unread 11-21-2021, 09:23 AM   #17
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Naaaa, the Laticrete commercial is off to one side of this page, JT.

You can certainly use that mortar if you want, but for less than half the price you can get mortars perfectly adequate to your StrataMat installation. And for bonding your tiles to the StrataMat.

The StrataMat installation may actually flatten the floor surface a tiny bit, but you can't count on that, and you'll need to be careful not to create any humps as you install it. Your floor must be sufficiently flat before you install that membrane.

The industry recommended flatness for the tiles you've chosen is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet. That's a very strict requirement and difficult to achieve in a wood framed floor. If your floor is not sufficiently flat, you'll need to address that before installing the uncoupling membrane.

My opinion; worth price charged.
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Unread 11-22-2021, 02:02 AM   #18
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I need some clarification on those tolerances.

Using an 6'6" foot level (the longest I have). If I place it on the floor it would indicate that my floor fairly level (about 1/4" over 6'6" feet). But in regard to flatnees, how do I apply the 1/8th over 10 or 1/16th over 2? Thats not in regard to level, its flatness.

If I lay my 6'6" ft level on the floor in the same direction of my tiling, there are not gaps between the level and the floor. If I place the level diagonal across the floor, I can freely slip a 1/32" shim under the level for about 12" (in the middle) but the 1/16" shim will not fit under it at any location.

I haven't installed the second layer of BCX yet. These measurements are on the 3/4" T&G.

Is this the proper way of measuring for the tolerances you indicated?

Thanks.
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Unread 11-23-2021, 08:02 PM   #19
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I am using Laticrete Multimax Lite as my tile setting mortar and decoupler mortar (if I install one).

The Laticrete data sheet states that I should use an adhesive between my subfloor (3/4 T&G) and underlayment (1/2" ACX). Is that correct?

I thought I wanted the two planes to be somewhat disconnected.

Thanks.

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Unread 11-23-2021, 09:39 PM   #20
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JT, unless you're bonding your tiles to the second layer of plywood, it is not your underlayment; the uncoupling membrane in this case would be your underlayment. In your case that second layer of subflooring is......a second layer of subflooring.

While I've always been a fan of gluing all parts of a wood framed subfloor to all other parts, when it comes to tile subfloors I've been converted by the authors of this article from our Liberry showing what I now consider the best method of installing that second layer. Caution: They also call that second layer an underlayment, which it is not.

As for the flatness, you want to use the longest straight-edge that will fit in your tile area and check in all directions from the high spots. If you can't use a ten-foot straight-edge, you'll need to extrapolate from what you have. You want the final floor before you set the tiles to be very, very flat. It will make your life easier and your final result look better.

My opinion; worth price charged.
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Unread 11-23-2021, 11:03 PM   #21
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DId I miss it? I didn't read anything in the article about adhesives between the two layers of plywood. The Laticrete Data Sheet says I should use an adhesive.

In regard to the level issue, the longest dimesion of tile is about 7'6". My level is 6'6". I'm still unclear on how to interpret the tolerances. If I place the level on the floor and there is no gap greater than 1/32", is that adequately flat?

Thanks.
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Unread 11-24-2021, 12:18 AM   #22
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No, you didn’t miss it. The article doesn’t mention or specify glue between the layers. Can you show us what you’re reading from Laticrete?

Quote:
Originally Posted by JayTee
I'm still unclear on how to interpret the tolerances.
To explain the flatness requirements of: ‘…the industry recommended flatness for the tiles you've chosen is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in two feet’…
…you could think of it like this. If you placed a giant piece of 10’x10’ glass on the floor, you don’t want any gaps under it that are larger than 1/8” anywhere. And if you were to place a piece of 2’x2’ glass on the floor and drag it around every last square foot of the floor, you don’t want any gaps under it that are larger than 1/16”.
So, when you ask…
Quote:
Originally Posted by JayTee
…If I place the level on the floor and there is no gap greater than 1/32", is that adequately flat?
It might be. But a level/straightedge is relatively narrow and not show you enough info to understand a 3 dimensional floor. The floor may be flat in one direction, but rotate the straightedge on the floor 90 degrees and it might be lumpy. You’d need to drag the straightedge around every last bit of the floor at every angle to more accurately evaluate how flat or lumpy your floor really is. Does this help?

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Unread 11-24-2021, 10:46 AM   #23
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Tool Guy,

Thanks for the tolerance explanation. Understood.

Since asking the question about to glue or not to glue, I've done some reading and there doesn't seem to be a consensus. In fact, it would appear close to a toss up.

Regarding Laticrete's adhesive requirement, it is on the Data Sheet for the MultiMax Lite product. It states:

UNDERLAYMENT: 5/8" (15 mm) thick exterior glue
plywood fastened 6" (150 mm) o.c. along sheet ends
and 8" (200 mm) o.c. in the panel field (both directions)
with 8d ring shank, coated or hot dip galvanized nails (or
screws); allow 1/8" (3mm) to 1/4" (6 mm) between
sheets and 1/4" (6 mm) between sheet edges and any
abutting surfaces; offset underlayment joints from joints
in subfloor and stagger joints between sheet ends; glue
underlayment to subfloor with construction adhesive.
Refer to Technical Data Sheet 152 “Bonding Ceramic
Tile, Stone or Brick Over Wood Floors”.

The link is here:

https://cdn.laticrete.com/~/media/pr...201210T193332Z

Thanks
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Unread 11-24-2021, 12:06 PM   #24
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JT, if you plan to use their bonding mortar and you plan to tile directly to the second layer of plywood underlayment, you should certainly follow their installation instructions, which I don't understand because it differs sharply from the tile industry standards. But product manufacturer's instructions always trump any other standards.

That said, I would recommend you not use any construction adhesive from a gun tube as you can cause more problems than you intend to solve. You'd need a full spread of their recommended adhesive and that's not easy to find in other than gun tubes and even more difficult to apply properly.

While we constantly recommend reading and following the manufacturer's installation instructions, consider that Laticrete is not the manufacturer of the plywood, be it used as subflooring or as a tile underlayment, and would therefore have no real authority over how it's installed.

Bottom line: If you want to glue that second layer to the first, do it correctly, but I don't think you need to glue it at all. I recommend you use the installation method I linked in post #20. See my warranty information below.

My opinion; worth price charged.
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Unread 11-24-2021, 01:41 PM   #25
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I've tried to keep with Laticrete's standard practices so far but I have to admit, I don't want to glue the two floors together. One reason which may curse me is that if anyone (me?) ever has to remove that floor, it would be a nightmare if its glued. I would plan on using 1-1/4" SS screws every 4" around the edges and 6" in the field leaving the appropriate gaps. I can't imagine that wouldn't be good enough. Hell, I think my current floor without the extra ACX is good enough with the Deflectolator numbers I have.

I'm now also going to put the Stratamat down. Its an extra step and I've never used a decoupling membrane before but I already bought it and might as well use it.

Have a new question. How long after a shower is tiled and grouted can it be used?

Thanks again. I'm sure I will be back with more as I start the tough stuff (shower pan install and Hydroban board) this week.
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Unread 11-24-2021, 02:46 PM   #26
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Quote:
Originally Posted by JT
Hell, I think my current floor without the extra ACX is good enough with the Deflectolator numbers I have.
The Deflectolator calculates only the deflection of the joists, JT. Has nothing at all to do with the subflooring.

Depends upon the grout you use.

My opinion; worth price charged.
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Unread 11-24-2021, 03:28 PM   #27
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Thanks.
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Unread 11-26-2021, 09:27 AM   #28
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Since it depends on the type of grout I use, should I use sanded or unsanded grout? My grout lines are going to be 3/16 on the floor and 1/8 on the wall. I dont want to use any epoxy types.

One more question if you dont mind, what are the pitfalls of using an adhesive between my plywood? You mentioned it could cause more more problems than its worth.
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Unread 11-26-2021, 09:58 AM   #29
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You should be using a sanded grout, JT.

First problem with trying to glue subfloor layers is not doing it properly. What you need is a full spread of wood glue of some type, which is not particularly difficult to do, but is a bit of a PITA to do correctly, especially with 4x8 sheets of material. And while I'm a big fan of gluing subfloor components, I cannot say I've ever enjoyed gluing two layers together.

Your choices there are a common wood glue, such as the Titebond PVA glues, or one of the specialty flooring adhesives such as Bostik's Best, or something from a tube gun such as PL Premium or one of the Liquid Nails products.

A full spread of glue, rather than random beads from a gun, are necessary to prevent voids in the gluing, which can result in soft spots in your second layer, which is generally thinner and can't well tolerate such voids.

That said, I've been convinced by one of the authors of the link previously posted that they could get "very close" to the same rigidity with their mechanical fastener schedule as would be achieved using a full spread of glue. He's a pretty reliable source, and their method is sooo much easier than gluing.

Then there is the existing data in the tile industry (which I've never seen) that indicates there may exist some small bit of "decoupling" available between the two subfloor layers that are not glued.

All in all, I've been swayed to the side that says the end joints at the quarter-span between supports and mechanically fastened is the better method of installing the second layer of subflooring.

My opinion; worth price charged.
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Unread 11-27-2021, 12:28 AM   #30
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The floor is 6' wide and 7'6" long with the joists running the 7'6" length.

I was planning on cutting my plywood 6' wide and 4' along the 7'6" length which would then require a second piece 6' wide and 3'6" long. This is to keep the grain of the underlayment perpendicular to the joists.

I am not planning to add the additional layer of plywood under the presloped foam shower pan. The pan is 2-1/2' to 3" thick.

As I originally stated, I would still secure the perimeter of each piece every 4" and the field on 6" centers and keep the appropriate gaps.
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