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Unread 11-08-2022, 10:08 AM   #1
jeffnc
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Cutting the perimeter of Kerdi pans

I saw an interesting video the other day, can't remember how to get back to it. But basically, when trimming Kerdi pans, of course you trim symmetrically to keep the height of the perimeter the same. For example if you need the pan 6" shorter and 4" narrower, you cut 3" off each of the ends and 2" off each of the sides.

But this does cause another problem, especially if you're cutting very far in, because now you have a perimeter edge that isn't the same height all the way around - it's only the same at each mirror image point on the tray. The corners will all be the same height, but it will dip slightly in the middles of the edges.

To correct that, the guy first cut off a 3/4" strip all the way around. Then he cut to the right size minus the 3/4", then he installed that strip around the edge of the pan when installing the pan.

Well, this is clever because it keeps the perimeter perfectly flat. But now the problem (which he didn't seem to address) is that you now have lip where the perimeter drops down to the lower height of the cut pan, and small tiles - typically 2" - have to span this lip.

I suppose it could be smoothed over with thinset during pan installation, and when set you're ready to tile. Thoughts?
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Unread 11-08-2022, 04:16 PM   #2
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The only thought I have is to mud the floor instead, saving money at the same time.
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Unread 11-11-2022, 10:03 AM   #3
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I'm having a hard time following the process, Jeff. You don't have a photo or a link to the video, do you?

It also matters where the drain is. The drain determines where the pan sits and what gets trimmed.
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Unread 11-11-2022, 12:56 PM   #4
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Can't remember the link. But it's a simple concept if I can explain it well.

Whenever the pan doesn't fit the space, you either have to get a bigger pan and cut it, or a smaller pan and fill in with mortar or whatever. Or both.

Example. You have a 64" x 40" shower space. You buy a 72" x 48" pan and trim it down. However you don't want to cut 8" off one end and 8" off the other end, because then everything will be unsymmetrical because of the slope. What you want to do is cut 4" off every side. Now every corner is the same height.

But now the problem is that because of the slope, the middle of the side edge is going to be lower than the corners, so you have a little work to do to level the tile, and then the gap will not be consistent.

But the pan out of the box has a perfectly level and flat perimeter, for a width of about 3/4". So if you cut that off first, then trim the pan the rest of the way, then install this perimeter that you cut out, your perimeter will now be level and flat all the way around.

But now the problem is you have a "stair step" down from that edge to the rest of the pan, rather than a smooth transition.
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Unread 11-11-2022, 01:33 PM   #5
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What Jim said about the location of the drain prevails. There is no good way short of a mud job if the drain is not centered.
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Unread 11-11-2022, 01:56 PM   #6
jeffnc
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Quote:
What Jim said about the location of the drain prevails. There is no good way short of a mud job if the drain is not centered.
The drain position is irrelevant in this case because you have the exact same situation even with a centered drain. The issue is the geometry of the Kerdi trays and the problem occurs regardless of the drain location and regardless of how much you trim on either side, but does not exist if you don't trim.
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Unread 11-11-2022, 02:25 PM   #7
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I know what you are saying, have to either live with it or do as you mentioned. Trimming more than a 1” creates enough of a issue that I wouldn’t try to correct it during setting . To me the point of the trays is saving time at prep ansometimes I mud and sometimes I don’t.
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Unread 11-11-2022, 03:41 PM   #8
jeffnc
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I think most people don't think of it because with the amount normally trimmed off, the dip is negligible, and people just make microadjustments to the bottom row of tile with wedges.
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