Removing a hump in my floor

[Golden]

I am looking for advice on the proper method to fix my floor flatness in order to prepare it for LVP “click together planks”. I am renovating 1050 square feet of my home and want to do it correctly. My home is 40 years old and built on a crawl space. When I go around the home with a 6 foot straight edge I find that it has sagged through the years and the center of the home down the central hallway that is over the center footer is high, and the floors sweep downward in both directions. It is well over the 3/16 requirement. I have a plan but want to make sure that it sounds feasible. Rather than trying to build up all of the low areas, I would like to reduce the hump that is over the center footer. My house has 3/8 particle board underlayment over felt tar paper which is over tongue and groove plank subfloor. I have started to remove a 30 inch wide section of this 3/8 inch particle board underlayment down the center of this hallway which leaves a 2 inch wide board down each side. Now, when I lay a straight edge from side to side it is about 1/8 to 3/16 above this center hump. My plans are to secure 1/8 inch thick hardboard (masonite) in this area that I removed the 3/8 particle board, then screed fill in the remaining area with some sort of trowelable filler (perhaps Ardex feather finish ?) to bring it up to level. Would this be the proper way to remove this hump?
Thanks in advance for you help.

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[C.J.]

If you’re talking about a 2” wide offending hump, why not just grind or sand down the particle board. Yeah you’re gonna eat up 1/4” of particle board in that area but a 60 grit belt or disc will make quick work of that as well as you can feather it out farther than the 2” strip.

 

[Golden]

I have removed a 30 inch wide section down the center of a 34 inch hallway, the 2 inch dimension is what is left of the particle board down each side of the hall to use for a witness or something to level or screed from.
The hump is probably as wide a a cement footer block, then tapers outward from there.

 

[C.J.]

Gotcha. Just reread your first post and you said that but I didn’t catch it. Smart idea. Lot less work than dealing with the structural side of the problem.

 

[Tile Tom]

As long as there's no deflection, that would probably work for a floater.
Sometimes thinking outside of the box works

 

[Golden]

Thanks for the replies everyone.
So, is it be okay to use the 1/8 " engineered hardboard (masonite) to replace the particle board that I removed? (It is not advertised as acceptable underlayment.) I also thought of maybe using using 1/4 sureply on the edges. I have a 30 inch wide area to fill, perhaps 10 inches wide of 1/4 sureply, then 10 inches of hardboard down the risen center, then 10 inches of 1/4 sureply again to total the 30 inches of width. This would reduce the amount of trowelable filler needed. Or is is better to forget all of the underlayment and fill it all with a trowelable filler? I have also heard of people using layers of roofing felt to fill areas. What are everyone's thoughts on that? Can it be filled over with a topcoat or is it too soft to provide a base layer?
Thanks again for the guidance.

 

[C.J.]

You can go up to 6 layers of roofing felt. 30# felt is 1/32” so 6 layers will get you 3/16”. What happens if you go 10 layers as opposed to 6? No idea but 6 layers is the magic number. If you’re going from 1/8” to 1/4” then from 1/4” to 3/8” I suppose you would be within tolerance but I think I like the idea you have of screeding patch right over the different layers of wood filler. I’ve done it and it works great. I would recommend you use a quality patch such as Ardex Feather Finish. Screed it out and wait for it to dry then skim the whole thing to make it look beautiful.

 

[Golden]

Okay, I am assuming that my layers of wood all need to be nailed or crown stapled down to my subfloor ? Then Ardex Feather Finish over that?
If I were to use roofing felt what is good to fasten it down with?
Thank You

 

[C.J.]

If I were to use roofing felt what is good to fasten it down with?

I’ve always stapled it down.