Question on floor leveling compound for the herd.

[IdahoDoug]

So, I'm about to lay down some plywood atop the old to stabilize the floor.  Plan to simply use several tubes of construction glue to fill the minor undulations between the old and new and run screws down to pull them together. Now thinking about using some leveling compound.

 

The question is, will the construction glue stick to the leveling compound strongly such that I'll have a strong bond between the new floor and the leveling compound?  And does the cured leveling compound provide secure grip for screws, or is it more of a soft material that will not work like that?  Thanks in advance.

 

 

[WME]

This is what I used to fill in the screw divots and things. It's old school but it is good stuff.

https://durhamswaterputty.com/

P.S. a little vinegar will slow the pot life. 

[linda s]

Rock Hard is not flexible and not waterproof. Yes floor leveler will adhere to adhesive. Think massive sheets of vinyl they use in malls. Those floors get leveled first. The procedure your doing is identical to preparing a floor with Luan. Standard for getting a smooth, strong  finish. Do not buy self leveling. Too messy for tiny motorhome. I always go back to this.

https://www.acehardware.com/departments/paint-and-supplies/patch-and-repair/spackling-compounds/1203413?store=04726&gad_source=1&gclid=CjwKCAiA3ZC6BhBaEiwAeqfvygstfRa1UthPoDOBQZMQnkKNYJm6P--hn0QH4Sz0wn35cV6QcqsXgBoCG6cQAvD_BwE&gclsrc=aw.ds

Easy to use

Linda S

[linda s]

Oh and screws. Remember that floor already in there is only 3/8 inch thick except for in the dinette post area. You want something that will grab but not too long. I like deck screws 

https://www.amazon.com/Exterior-Threads-Anti-Corrosion-Outdoor-IMSCREWS/dp/B0BJTYMXMP/ref=asc_df_B0BJTYMXMP?mcid=29e8cac572033881927a6c8b889acbc6&tag=hyprod-20&linkCode=df0&hvadid=693270340296&hvpos=&hvnetw=g&hvrand=5001550553341085710&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9222860&hvtargid=pla-2187309422879&psc=1

[IdahoDoug]

Thanks for the tips.  I got screws like Linda has pictured, as I wanted the unthreaded shank she shows, so it would be more effective at "pulling" the lower original wood against the new wood.  

 

Wow.  This is going to be more work than I'd hoped but certainly worth it.  More work than expected, simply because it wasn't until yesterday that I am ready to lay down the new subfloor and grabbed a 6 foot straight edge and started checking things out. The builder certainly didn't do me any favors with their seams in awkward spots where it would have been wiser to put seams in more stable areas such as the steel crossbeams.  I will certainly fix that, and last night built a pair of 4X8 butcher paper pieces to lay down and trace to make accurate patterns.  My pieces will be unbroken plywood over areas where 3 seams oddly came together, giving much better strength by tying them all together with wood and screws. 

 

So, check my logic on this.  In the interests of preserving hard fought headroom down the center aisle, I am thinking of using pure glue to fill what will start as a half inch sag (largest, which is about 18" long) rather than the levelor product I asked about.  With the levelor, the "trench" will be filled/built UP to the brim/highest points, then new plywood will be laid down atop the highest points.  With construction glue, I'll have glue in the trench, then use screws to pull the new plywood firmly downward and the two pieces will "meet in the middle". The old plywood will be pulled up a bit and the new plywood will flex downward a bit and glue will be squeezed out. Should end up with the new plywood 1/4" or more lower than the leveling method would produce, with the downside I'll have some faint but real unevenness.  Doesn't seem like much, but the headroom gain difference is important considering all the effort and time I spent arcing and reinforcing the roof to gain headroom. Strength should be the same with either method though a slight edge for the glue as it will harden and make a stronger "sandwich". 

 

For clarity, nothing but glue and screws - no leveling compound.

 

And of course the actual flooring I'll later add is going to raise the floor further.  I'm planning to use a marine flooring product that is put down as a sheet, so it will not be wood or planks, which benefit more from perfect flatness.  This product is more akin to a high density foam and you'll see it on swim platforms or cockpits on high end ski boats.  It's grooved to give the impression of the classic marine "teak and holly" flooring that's been a mainstay of yachts for centuries.

 

Comments?

 

 

 

[linda s]

Just so you know how much that bottom floor will grab, try putting a screw in to only that in an out of the way place part way and see if you can pull it out with pliers. Pick a spot that looks nasty. If it stays firmly, your good. Can't pull 2 pieces together if one of them is mush

Linda S

[IdahoDoug]

Good to know, and the good news is the low spot in the hallway is solid - no water damage - , so it should pull very well.  The deteriorated foam under it simply allowed the wood to sag with use over time due to a lack of support under it. The only damaged spots of my floor were the back corners and they've both been impregnated with resin, then 3 layers of fiberglas atop that.  But I won't need to pull those up as that's simply storage and I won't notice a half inch of slope when it's buttoned up.  I'll use weights to press the new wood/ glue down there, vs screws.

 

I'm laying down new high end Baltic Birch 1/2" plywood and have high hopes it will deflect downward only a little while the 40 year old 3/8" original flooring should come up a lot when using screws to pull them together.  The trick will be gently tightening each screw in turn and then going back and doing it again. Otherwise I'm sure I can strip them in the old wood if not careful by just pulling on one screw too hard.  I am tempted to drill a couple holes in the new plywood to confirm this movement visually, but am afraid I'll just create glue squeezout.  I guess I could cut a sample of the birch and see how well it pulls the low spot up, but then I'm putting holes in the old plywood which later will have glue squeezout on the bottom. Hmmm.....

 

Leaning toward using just glue after speaking to a buddy who owns a construction business. He says even if it's over a quarter inch thick it will still cure but will take a while with outside temps here in the upper 30s, but is more confident of the ultimate strength this way.   I'll use heat lamps of course.  I'd prefer the ultimately stronger and lower floor sandwich with very slight undulations, over leveled but raised old floor and its loss of headroom however slight.  I'll report back - thanks.

Edited November 26 by IdahoDoug

[WME]

I used the Water Putty to fill in the divots where the screws were, not for leveling the floor.

IF you can cut the new floor for a proper fit, lay it down and drill 1/8" holes through the new floor and into the old floor. Remove the new floor and drill a 1/2" hole in the old floor and glue in a proper length 1/2" dowel. With new flooring place screw it down into the dowel. Much stronger.

[IdahoDoug]

Thats a good idea, but would add a lot of extra time to increase the holding power of the screws. I think I will get sufficient holding power after some testing yesterday and swapping screws to a better type. Once the glue cures, I will have a very strong subfloor by essentially combining new and old into a 3/4 inch laminate.  The first piece is cut.  I will update on my big thread....

[TheMullet]

IdahoDoug, 

Within the last week I finished this l exact job. I started by sanding the existing sagging floor. After, I put on some Henry’s 345 leveling compound to the area near the sink to help make the floor more flat. I will say, that it took two full days to dry due to the thickness of it and not applying it in thin layers. Once it was done, it was closer to flat but definitely not perfect.
I then applied a sheet of 15/32 ACX Plywood down, with Loctite PL400 subfloor glue beneath it. After, I installed screws every six inches on the perimeter of the wood, and approximately every 12” in the middle. Once I was done, I installed vinyl plank flooring down followed by quarter round. This floor is not perfectly flat, but it’s leagues better than it was before.  As for height, I'm 5’11”. With it all installed, my hair slightly grazes the ceiling but not bad. I just won’t be wearing cowboy boots in there anytime soon. 

[IdahoDoug]

Nice - looks fantastic!!!  Great job and I bet its nice not feeling the floor trampoline every step, eh?  Well wish me luck, heading out in 5 minutes.