Removing a high spot

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highup

Will work for food
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Hard to describe, but I'll try.
The high area is on a foundation where new and old meet. The "new" is over 30 years old.
I'll start with my laser measurements.
On the two underlayment seams marked with blue tape, I get 4 1/2"
Half way between the tape is the existing foundation. It sets higher and measures 4 1/4" creating a hump.
 

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The far side is the older part of the home. The construction on that side is 2x6 t&g fir, supported by 4x8 timbers on 4' centers. It's extremely solid, no bounce.
Directly on top of the t&g, is 1/4" plywood....... and on top of that, is some 1/4" Weyerhauser Structure wood underlayment. It looks like it was installed yesterday.
The newer side of the kitchen is newer I-beam construction. It may have two layers of 3/4" plywood, plus the 1/4 inch Structurwood.
Ok, I'm removing the entire 4 foot section of underlayment between the two pieces of blue tape.
Once the underlayment is removed, and I place level across the remaining underlayment edges, the level will touch the foundation area and the hump will be gone.
Yay!
This will form two wedges, one on the old and one on the new sides of the room.
The wedges would each need to befilled from 1/4" to zero ....zero over the foundation area and 1/4" where the underlayment was removed.
These side view drawings might help describe it better.
 

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With all that info, my question is, would it be wise to do the majority of the filling with wood, either 1/8" Masonite or a door skin?
That would mean less filler.
I'd be fully gluing and stapling the Masonite or door skin material.
I think using wood a a partial filler would be more durable, less prone to cracking over time.
 
With all that info, my question is, would it be wise to do the majority of the filling with wood, either 1/8" Masonite or a door skin?
That would mean less filler.
I'd be fully gluing and stapling the Masonite or door skin material.
I think using wood a a partial filler would be more durable, less prone to cracking over time.
What’s being installed? Floating floor?

Sanding sounds right…

But if not how about some undercourse/shims/cedar shake Instead of Masonite? Might be able to get it closer to flat with less or no patch.
 
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On the left hand side of the drawing, the far side of the photo, is a layer of quarter inch plywood over 2x6 tongue and groove, capped with this quarter inch Weyerhouser Structurwood quarter inch underwood what you see covering the entire floor.
If it were possible to sand that OSB type underlayment evenly, the center part all along that high area would be 1/16 of an inch, feathering to paper thin. There's no way to fasten that.
Now, if this surface that you're looking at was that 1/2 Weyerehouser gold edge underlayment you'd have a better chance at sanding because they'd still be some meat left.
 
What’s being installed? Floating floor?

Sanding sounds right…

But if not how about some undercourse/shims/cedar shake Instead of Masonite? Might be able to get it closer to flat with less or no patch.
I'm tapering from one quarter inch to zero over a 2 ft wide area. I'm just trying to avoid a quarter inch of filler mainly because of the structure of the old part of the house, look at the left side of the drawing.
It's 2x6 tongue and groove with quarter inch plywood on top and then this quarter inch OSB is the current finished surface.
I'm trying I'm trying to avoid a quarter inch of filler at the beginning of the ramp and want to glue in 1/8 of an inch of solid material just to make it more stable. The floor feels very strong, and has no bounce but still I'm just trying to avoid doing the entire area in a wedge of filler. Two wedges, one on each side of the high spot.
This is a better picture than one of those I showed earlier. Picture what I drew instead of a ramp down, it's a ramp going up to the high spot but same scenario.
only tapering from quarter inch to zero.
 

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The flooring going in is a vinyl plank material made by XL flooring.
It's 1/4 in thick, and no tongue and groove. I can be loose laid or glued with pressure sensitive.
Because of it being largely a kitchen area I was planning on gluing.
 
I'm not a flooring pro, but this is just a wild hair idea from an overthinking problem solver.
IF you can access under the floor, could you drive wedges between the support beams & the layer of subfloor directly on top of them? If not that, maybe use an appropriate beam & jack to raise it & insert glued shims? That way, all the layers remain intact without having to create the big tapered pieces or have a feather edge. If it's a viable plan, you could taper the slope back a ways by doing this on multiple beams with thinner shims. There could be a slight ridge where the sections meet, but I'd think a belt sander would make short work if it.
There might be 1,000 reasons this won't work. I was taught to always share a brainstorm idea, even if it's not a good one. It might spark a more appropriate idea for someone else.
If that idea is totally wrong, could you get the gradual slope you need with a wood floor refinishing sander tapering down the high side (possibly followed by cement based leveler to fine tune it)?

Happy leveling.
 
Then you really don’t have to worry about getting that hump completely flat… One more vote for sanding. Or just a little patch on either side to lessen the severity….

But I‘m guessing you want it perfect…😎
I put on my headphones, cranked up some Sinatra and did it my way. It's not about speed, ease, or $$$. Once the underlayment was removed, I placed a 6' straightedge across the span and it just barely touched the center in a couple spots. Less than 1/16" high. 80% was dead on. This shows that the edges of the underlayment and the exposed high spot are perfectly in line.
Along the foundation span, it's perfectly flat.
I moved a 3' straightedge across each span, and using a scrap of 1/8" masonite, mapped out where the new masonite should end. The masonite isn't going anywhere. I zig zagged 1/8" beads 1" apart under the entirety of each sheet. I rolled it, then shot it down with the electric tacker.... The staple rows are 4" apart and it's stapled every 3 inches. Much closer on the edges 😱 The staples are only there to keep the sheets embedded in the adhesive. The masonite and the plywood have become one. 😁
I only got the initial fill on one side done and it got too late. I'm going back today to do the initial fill on the second side and finish the side by the fridge, because I want to slide it back in place tomorrow while I finish up the prep. I want the chefs work area kept in full working order.... You know why. 😉
Overkill? Like I said before, speed and money aren't a concern. I know for most guys, most jobs, there is a time frame and budget to get it completed. Not the case here.
 

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