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Unread 03-22-2021, 09:47 PM   #1
Registered User
Join Date: Jan 2021
Location: Toronto, Canada
Posts: 6
SLC issue, Ditra heat going on top

Hi all, I've been lurking for a while and now a reason to post. I'm re-doing our 5' x 13' second floor bathroom and on checking the wood subfloor, I found that the floor was out of level outside of the (to be curbless) shower area. The middle of the floor was the highest point, and the floor against the worst offending wall was about 3/4" lower (just because that part of the house is old, I think). So, a few YouTube videos later and I'm pouring down Sika 125 SLC. Seemed easy enough I thought...

Well, I put down two bags after priming the 5' x 10' non-shower area and then I re-measured using my laser level and I'm still off, this time by about 3/8" in the worst area.

And this is where I likely made some bad decisions -- I was thinking, John Bridge says I need the floor height within 1/4" over 10 ft. Also, I am prepping a curbless shower, where I've lowered the subfloor into the joists (using the Ebbe kit, which was great btw) and thus I don't want to put down too much SLC and raise the entire floor up too much, or else the Ditra heat won't line up well with the curbless shower. Basically I didn't want to add more SLC to the highest area of the floor so I drew a topographical map of sorts on the floor and planned to selectively pour a third bag of the Sika 125 SLC over the two lower areas that still needed it.

At this point, an error prepping the SLC. The bag ripped, an unknow quantity of water that had been perfectly weighed flew out of my bucket and so the SLC was likely a bit thicker than it should have been. A "new" highest floor area was born! I didn't want that area to win so I grinded it down with my angle grinder and a concrete disc (which was a horrible job obviously). I succeeded in bringing it down to the same height as the original highest floor point and now, I am left with a floor that is only 1/4" off in the 10 ft, BUT there are numerous 1-2 mm low areas given the uneven pouring of bag #3 of SLC.

I have attached some pictures. At the end of the day, Ditra heat is going down and the floor will then be covered in 6" hexagons that are 3/8" thick.

My options I think at this point are:

1. Lay the Ditra and then tile as usual, as though I've got a perfect substrate. If this doesn't turn out great though, my wife will be angry and I'll likely never hear the end of it. She's already less than impressed with the delays caused by the SLC issues.

2. Scrape up all the SLC and start again. I really dread this option. If I do this, I will have to re-prime and use all three (or more? I don't want to use too much as I need my floor + Ditra to line up with the curbless shower) bags at once. Maybe I should draw my map again on the wood subfloor and buy those little sticky floor levelling pegs/rulers and pour just on both sides of the highest floor area, to help prevent unnecessary build up??

I'll abide by the expert advice provided here. Thanks.
Toronto, Canada
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