Underlayment Preparation for Glue-down Flooring

[Augustine]

Preparing to lay down 5/16 hard-wood flooring, after removing the carpet, I noticed that the wood underlayment was splashed with paint from the walls and blotches from the pop-corn ceiling.

I figured to remove them with a belt-sander, but it proved to be a lot of work. Not to mention the fine dust all around the house.

Is it really necessary to remove the paint before gluing the floor down?

Another question: how to figure out the structural beams direction under the underlayment (the floor is supposed to me laid down perpendicular to them)?

On a side note, the belt sander seems to fairly effective to level adjacent underlayment panels.

Any advice to a weekend handy man?

TIA

[roger61611]

I would think you just need to get down to wood so the glue sticks, right ? Also the nailing pattern should be evident; if you have an 8x4 sheet of plywood, either the 4' ends or the 8' ends will have nails more often. That's the direction the joists run.

[Augustine]

Yep, that's what seems to be the idea.

Right now I'm split between renting a floor sander and replacing the underlayment. The tiny 3x21 belt-sander makes it worse that it already is...

It's not very clear which side has more nails. Some sheets have more on the 8' side and others, on the 4' side.

Unfortunately, a stud-finder was not of much help...

[hallerb]

try looking from below or the attic to see which ways the beams run. or ask a neighbor, someone else may have aleady figured it out

my doorbell was missing when we moved in here. I went and looked at a neighbors, neasured theres location and found my wires within minutes wallpapered over

[Augustine]

Would laying 1/8" plywood sheets on top of the existing underlayment be OK? At least installing them would beat sanding 1000 sq. ft. with a 3" x 21" belt sander... :-}

[Justin West]

What helped me was looking in the basement where the main structural support beam ran. From this I knew the joists ran perpendicular across it. Typically the entire house would be the same.

That being said, I am a novice when it comes to this. So take me with a grain of salt please. :)

JW

[Sacramento Dave]

If you have a plywood subfloor it should be a minimum of 5/8" thick it could be more. What I did was scrape any glue,sheetrock mud, paint or any thing sticking up. Any nails sticking up in subfloor hammer down. You should be able to see the nail pattern on the subfloor. The joist should run in a 90 degree angle to the 8' length ( joist do change direction sometimes) of the plywood Joist should be on 16" centers. I really don't think the joist are important for what your doing. What I would do is lay down a Vapor barrier over the existing subfloor. or over uderlayment. Then nail 3/8" AC plywood over that for your Glue surfaces. I used 7 penny galvanized nails 6": on center in the field and 4" O.C. on the edges.You don't want to match the plywood underneath avoid joints on joints. Putting down 1/8 ply. would be pointless. Why are you gluing and not stapling the floor down. You can buy a floor stapler for about $205.(

and I guarantee there's a whole lot less mess.Another point is the staple will go threw the 3/8 underlayment and into the subfloor. Getting your underlayment joints on a joist really dose not matter. The flooring should have installation information and preparation. Is it a prefinished flooring T&G?

[Augustine]

I think that what I see, after the carpet was removed, is the underlayment, not the subfloor. It's 5/8" thick, but there's about

1/8" spacing between the sheets. That's why I think it's the underlayment.

Due to the state it's in, I'm thinking about laying 1/8" sheets to glue the floor on. I say 1/8" to limit the height increase.

I'm using this product:

Nailing does seem to be faster, but because downstairs it'll be installed over the concrete slab, I thought that gluing down in all the house would be fine.

Besides, Bruce says that it can be stapled down. Is it any different from nailing down?

Thanks.

[Sacramento Dave]

Nailing does seem to be faster, but because downstairs it'll be

The usually don't put underlayment under carpet. How old is the house? 5/8" thick would make me think it is subfloor. I've never heard of 1/8" for underlayment, if you use that you better glue it down. I had the same situation in my house concrete and wood . I used staples ( I still call it nailing) were I could and glued the concrete that's why I say you should staple what you can. The raised floor where you installing the hardwood . If there is just foundation crawl space under it you should put a vapor barrier down.

[barry]

IMHO I'd _never_ use a belt sander to flatten a surface. Never.

Maybe a 6" ROS, _with_ shop-vac connected, if used very carefully.

Joists should run perpendicular to load-bearing members below. There should be essentially wall-to-wall partitions down there. Know any carpenters to ask?

J

[Augustine]

The house is 13 years-old. And after giving it a thought, I agree that what I see is the subfloor.

Laying down 1/8" sheets will make the transitions to other kinds of flooring 1/8" higher, which may cause issues with the transition pieces fitting.

Another alternative would be to replace the subfloor, but this is getting on my nerves. Nailing down is becoming the most attractive alternative for upstairs.

Any tips on gun nailers? I wouldn't mind having a corded, electrical one if it can do the job.

TIA

[Sacramento Dave]

I bought the spotnail model WS4840 W2 about $200. In my area I could not find one to barrow or rent and you will spend more renting. I don't know about an electric ones. Well if you use 1/8" uderlayment nail it down good but the flooring staples will hold it also. I don't no what to tell you about the transitions. They never come out the same. On mine I milled all my own trim and transition pieces. I also had 3 steps down in one area and 4 steps down in another. So I just made new stairs. I have a complete shop in my garage and to many years of experience. Once you get laying the floor it's pretty easy straight forward but when you come to a wall you will have to rip some boards also the stapler dose not fit. so you need a pin nailer or nail by hand. So you will run into some problem solving situations. Oh be sure it will take longer than you think like anything, but at the end the reward of I did is there.

[Augustine]

Armstrong mentions both

Both require an air-compressor, which I'd have to buy too (recommendations appreciated).

I'm also buying a cheap ($120) table saw to rip the strips near the walls. Or would perhaps a circular saw and a bench do?

The prospect of nailing the strips upstairs is not bad, as it seems to be faster and less messy than gluing. Downstairs will have to be glued down, though. Doing otherwise would be as cumbersome as gluing upstairs. I'll be installing a total of about 1600 sq. ft.

The last touch will be to install new base boards, as the current ones are just door moldings with a too uneven surface to attach quarter rounds to. But this seems the easiest step, relatively speaking.

Thank y'all for the tips.

[Augustine]

I also noticed that the subfloor was nailed with bright nails, not shank nails. The seams have no adhesive between the sheets either. So besides having to sand the transitions between sheets to make them level, would it be prudent to replace the nails and fill in the gaps too?

TIA