Please evaluate my subfloor

[EllenEL]

Lifted carpet, found 3/4 plywood 2003 build, nails used.

There are smaller dips but at least one area goes 1/2"

Will be installing floating floor, engineered wood, Kahrs across joists, which are 16" apart.

Planning to put additional screws. Not sure how generous I should be.

Also should I place transition at closet line? I have trackless bifold doors there.

Exterior wall by the windows has air vents. Opposite side has Master bathroom door.

Kahrs manual suggest roofing felt paper for dips. I am thinking deepest dip should have Ardex FF added?

 

[C.J.]

So the part of the house that dips down as it gets closer to the wall, is that a second floor room with an overhang? As in the upstairs part of the house hangs out further than the first floor?

Building up layers of roofing felt is a good idea. Technically you are only supposed to go up to 6 layers. 30# roofing felt is 1/32” thick. That gives you up to 3/16” of an inch build up. For 1/2” I would use layers of 1/4” plywood to fill in the deepest part then feather it out with Ardex FF. Mix it with some P51 and it’s damn near bullet proof and will handle any slight seasonal structural movement without breaking up.

I’m not a fan of transitions at closet doors. Just doesn’t look right.

 

[EllenEL]

This is second floor however there is no overhang except bay windows on second floor. I wonder now if that what causing end of the floor sagging?
Thank you so much for responding!
Am new to using Ardex and p51. Am thinking I would move my board and map low spots. Then cut free shaped felt paper and staple it at the edges?
I will get plywood and glue it? Then apply Ardex and feather it out. When do I use p51?
I have used Henry patch and found it to be very sandy in texture. Am hoping Ardex more like thinset?
Am new to floor prep, have installed laminate and vinyl in previous house and have learned from it.
So am very much appreciate any advise!

 

[C.J.]

This is second floor however there is no overhang except bay windows on second floor. I wonder now if that what causing end of the floor sagging?

It is. Think about it, all the weight of that part of the house is resting on your joists which are supported 2’ back from where the weight is bearing down. How old is your house? That’s how many years your joists have had to slowly sag even if it’s only 1/2”. No biggie. Float your subfloor up 1/2” and forget about it for another however many years.

P51 gets mixed in with the Ardex in place of some or all of the water. It gives the floor patch strength and helps resists cracking if there is any slight movement.

 

[highup]

So the part of the house that dips down as it gets closer to the wall, is that a second floor room with an overhang? As in the upstairs part of the house hangs out further than the first floor?

Building up layers of roofing felt is a good idea. Technically you are only supposed to go up to 6 layers. 30# roofing felt is 1/32” thick. That gives you up to 3/16” of an inch build up. For 1/2” I would use layers of 1/4” plywood to fill in the deepest part then feather it out with Ardex FF. Mix it with some P51 and it’s damn near bullet proof and will handle any slight seasonal structural movement without breaking up.

I’m not a fan of transitions at closet doors. Just doesn’t look right.

That's the same thing I would suggest using the quarter inch plywood out as far as it will go until you need to start with filler.
It would probably be a lot cheaper to use quarter in Masonite. You just want to leave a gap when you place one section against the next.

 

[highup]

On cars floors that were to be put on concrete, at one time they recommended filling a low spots with sand. Yes when there's sand on the floor your foot will displace it. Once you lay the floating floor over the sand your weight is displaced so much the sand stays right where it is.
I never tried that on any jobs but it was interesting and the reasoning in my humble opinion, was quite sound.
There's nothing wrong with using floor filler instead of tar paper.
Maybe use the tar paper if you map out a circular depression and progressively make larger and larger circles until it is flat. There's more than one way to flatten out a floor.
In that second image where the floor starts dropping the last few feet. If you move your level all the way across the floor at that same point is it consistent?
Now, if you turn your level 90° to make it parallel with the wall....... Is that area flat? If the answer to both questions yes then by all means use plywood or Masonite to fill in the majority of that depression. It's a lot easier than trying to use filler clear over to the wall

 

[C.J.]

Plywood is cheaper than patch and won’t break down. You would use the plywood in the exact same way as you would use roofing felt by layering it in a topographical style to fill in the low spots. If you do it right, when you go to fill in the voids between the layers all you’re doing is essentially dragging your trowel across the top of the different layers to fill in the 1/4” to nothing taper. Of course you will need a couple coats to really smooth it out but if done right it works like a champ. I’ve got some pictures on my old phone of a job I did where the house dipped an inch. Put your straight edge down and fill in the low spot in layers then fill in the 1/4” to nothing taper. Nothing to it. I’ll have to get the wife to figure out how to get the pics from my old phone so I can post them. Once you see how easy it is you’ll be all over it like Donkey Kong. Gimmie a bit and I’ll try to post them after I’m done workin.

 

[highup]

I will second what he said.
When doing a coat of filler to do your taper from the edge of the plywood.....
Don't try and make it flawless in one pass. Fill it as close as you can without overfilling it then scrape any ridges off before it totally hardens.
Mix a slightly thinner batch and use that for your second or second and third coats to finish flattening the area. There's no reason to try and make it flawless in one coat. Take your time and do it in steps just do not overfill it. These four patches dry really hard and do not sand very easily.

 

[Commercial Floor Rep]

Slight observation....

P51 is NOT an admixture. It is a primer only. If you've ever mixed it into an Ardex product, then you've been lucky that it didn't fail. If more elasticity is needed in extreme situations they make an additive specifically for K-15 self-leveling called E-25 resilient emulsion. That's really the only additive they offer and it has a very specific product use (K-15). Their products are already polymer modified (in dry powder form) right in the bag. That's one of the reasons their products have shorter shelf lives than others. Although, candidly, the product will still generally work after the date it will just begin to dry more slowly than normal.

The only self-leveling Ardex product that's usable over a wood substrate, as is straight out of the bag, is Ardex GS-4. (K-15 can be used with the above mentioned E-25 additive over wood substrates as well) I would strongly urge you NOT to use a self-leveling unless you've used one before. They are not the easiest products to work with and timing is very sensitive. It's a multi-person operation so you would also need 2-3 more people to use a selfleveling product.

If you need to fill in a deeper drop like this it would be better to use Ardex SD-P trowelable floor patch. You can actually "screed" this product if needed. It can even be used to create "ramping" where needed (not your application but for general information).

We've been an Ardex distributor for years and I've been through their schools multiple times so I'm pretty comfortable with their products as well as the Henry patching products (avoid them if at all possible) sold in the boxes.

Hope that helps and wish you well with your project!

 

[C.J.]

Slight observation....

P51 is NOT an admixture. It is a primer only. If you've ever mixed it into an Ardex product, then you've been lucky that it didn't fail. If more elasticity is needed in extreme situations they make an additive specifically for K-15 self-leveling called E-25 resilient emulsion. That's really the only additive they offer and it has a very specific product use (K-15). Their products are already polymer modified (in dry powder form) right in the bag. That's one of the reasons their products have shorter shelf lives than others. Although, candidly, the product will still generally work after the date it will just begin to dry more slowly than normal.

The only self-leveling Ardex product that's usable over a wood substrate, as is straight out of the bag, is Ardex GS-4. (K-15 can be used with the above mentioned E-25 additive over wood substrates as well) I would strongly urge you NOT to use a self-leveling unless you've used one before. They are not the easiest products to work with and timing is very sensitive. It's a multi-person operation so you would also need 2-3 more people to use a selfleveling product.

If you need to fill in a deeper drop like this it would be better to use Ardex SD-P trowelable floor patch. You can actually "screed" this product if needed. It can even be used to create "ramping" where needed (not your application but for general information).

We've been an Ardex distributor for years and I've been through their schools multiple times so I'm pretty comfortable with their products as well as the Henry patching products (avoid them if at all possible) sold in the boxes.

Hope that helps and wish you well with your project!

The Ardex rep told me not to mix P51 with FF but I’ve seen others do it and I’ve done it myself at times with success. Lucky? Maybe. You’re supposed to mix P82 with FF to use it as an embossing leveler although I’ve never done that. Usually I just mix FF straight and it works like a champ. Never have had FF fail on me even if I’m not doing things by the book. Might not say much about me at times as much as it does say about Ardex.

 

[EllenEL]

Really appreciate! I have read about sand for Kahrs floor and it sounds simple, I think I will be comfortable with felt paper. Today I reinforced each nail that was sticking out with deck screw.
It does seem fairly level if I put it across the dip, it stands to reason that bay window pulling middle down, as it goes towards corner it decreases.
Also do I fill the gaps between plywood with Ardex too? And all small imperfections tiny dimples? How good is good? I am generally tend to be on perfectionist side, what is good enough?

 

[highup]

With a heavy wood floor product I don't think there's any need to fill those gaps between the plywood panels. If you lay a straight edge across those panel edges and there's a dip there, only then would you want to fill those. Don't bother with dimples, hammer marks and other small stuff.

 

[EllenEL]

Thank you very much! I feel better and more confident with your advice. I will update after instal.