# Questions on underlayment for sheet vinyl



## Lone Wrencher (Jul 7, 2005)

I'm doing a bathroom remodel. There was significant water damage, so I gutted the room down to the studs and joists. I replaced two joists and laid down a 3/4" CDX plywood subfloor.

The finish floor will be sheet vinyl. The only thing I'm not sure about is the underlayment. I could use 1/4" Luan or 1/2" underlayment-grade plywood. Luan is cheaper, but from previous threads I've read so far (I'm new to this forum), some of you guys dislike Luan.

My questions are:

1) Do I need to lay 15# felt (tar) paper between the subfloor and underlayment, or is tar paper only used if you're installing hardwoods?

2) I used subfloor adhesive when I laid the subfloor on the joists, but should I also use the adhesive between the subfloor and underlayment (whether it be Luan or plywood)?

3) If I use Luan as an underlayment, is it okay to screw it rather than staple it down? Wouldn't screws make for a more secure installation? Speed is not a factor on this job.

4) Do I need to leave a 1/8" gap between sheets of Luan? What about sheets of 1/2" underlayment plywood?

5) What do I use to fill the seams/fastener dimples before laying the vinyl?

I'm a plumber, so this is my first real flooring job. Any advice will be much appreciated.

Thanks, Ken


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## CARPENTERDON (Jun 30, 2005)

Lone Wrencher,

I use 1/4" Luaun under all sheet vinyl flooring jobs, it works great!

Here is how I do it

1. Glue (const. adhesive) and screw the luaun to the subflooring. Keep all the butt-joints of the luaun tight. Also make sure to stagger the joints. 

2. I use a latex filler (recommended for use before laying vinyl flooring) to fill in any crack in the seams and the screw heads. For assurance allow filler to dry for 24 hours prior to laying vinyl. Doing this will give you a nice smooth flat surface to lay the sheet vinyl over.

3. Dry fit your vinyl and trim to size leaving an extra 1" for fudge factor.

4. Fold back one half of the vinyl (DO NOT allow the flooring to crease along the fold) and start applying flooring adhesive, using a 1/8" V-notch trowel.

5. Once the area is covered with the adhesive, reach under the folded over piece of flooring and roll it from the center of the fold out, working the air bubbles out with your hands. Once the one side is down fold back the other side and repeat.

6. After all the flooring is glued down, take a 100# steel roller (available @ most rental centers) and roll the flooring down from the center out (doing it this way gets rid of all the air bubbles that may be trapped under the flooring.)

7. Trim the edges and install base mouldings. :Thumbs:


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## Floorwizard (Sep 24, 2003)

Manufacturers will not warranty any problems if Luan is used. So I would prefer you use AC grade Plywood.
But it's a free country...


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## Don Benham (Mar 17, 2004)

luaun is crap. Full of voids that won't reveal themselves until after installation. Definately NOT recommended.

What you want to use is 1/4inch or 5mm Birch Underlayment. Halex makes it, so do a few others. It's always well made and tested to be solid. 

Don't but the edges of the panels tight, I place a business card between the joints to allow movement.

Staple it with 1inch narrow-crown underlament staples. No glue. Just staples. Then lightly sand the seams with a belt sander if nessaccary. 

You can patch the seams with a portland based leveler like Ardex. Ardex is the best bar none. Other companies make it and all are better than using a gypsum based patch. You want a grey patch and not a white patch. But patch is only nessaccary if you full-spread which is asking for trouble. 
leave a 1/16th gap around all fixtures.

Or you could hire a flooring mechanic and have it done right.


HTH
Don


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## Lone Wrencher (Jul 7, 2005)

What is AC grade plywood? And how does underlayment-grade plywood differ from regular plywood?




Florcraft said:


> Manufacturers will not warranty any problems if Luan is used. So I would prefer you use AC grade Plywood.
> But it's a free country...


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## Lone Wrencher (Jul 7, 2005)

I assume you prefer the perimeter-bond method of laying sheet vinyl. Actually, this is my second bathroom floor. The first one I did was in a basement on a concrete slab, I used LevelQuick floor leveler and Henry (which I believe is made by Ardex) patching compound. I did a permiter bond installation, but I installed the plumbing fixtures (fiberglass tub/shower unit, closet flange and pedestal sink) AFTER I laid the vinyl (I had the luxury of doing this since it was new construction. It's been in six months and looks good so far.

I've been thinking of doing this floor using full-spread since it's over a wood substrate, but why do you say full-spread is "asking for trouble?"




Don Benham said:


> ... patch is only nessaccary if you full-spread which is asking for trouble.
> Don


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## Don Benham (Mar 17, 2004)

Joint telegraphing. Most manufacturers allow a perimeter bond or even loose laying. Must more forgiveness especially if you're not too experienced. Prep-work is much easier than if you full spread the floor.

Don


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## Floorwizard (Sep 24, 2003)

Lone Wrencher said:


> What is AC grade plywood? And how does underlayment-grade plywood differ from regular plywood?



Underlayment grade (AC) is sanded and smooth and ready for vinyl.
Multiply is an example.

There are other grades of ply that are not suited for vinyl, but would be good if you lived in Florida and had alot of windows


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## soxfan (Aug 2, 2005)

Not all luan is the same. There's sheets that simply aren't designed to support a finished floor and therefore shouldn't be used as such. However some types are just fine. My local distributer stocks luan that comes with a 15 year warrantee as an underlayment for most any type of vinal. Its a bit more expensive than the standard Home Depot stock, but its much more reasuring. 

btw luan is pretty much designed to be tossed out with the finished floor when the finished floor's time is up. So please, please, please don't screw it down! Think about the poor sob who'll have to demo it 15 or 20 years from now. Staples designed for the task are best. A properly set nail gun is second and hand-nailing is a less than ideal but not horrible third choice. Honestly, glueing is a waste of time imho.

btw, any bump or depression that you can feel with your fingertips at all will telegraph through the vinal. That's why staples are ideal. They'll secure the underlayment firmly without denting it.


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