1/4" Plywood Underlayment

Old 11-17-02, 10:32 AM
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1/4" Plywood Underlayment

Here's a question for any vinyl pro's out there...... have you ever had any problems with plywood underlayment joints telegraphing through sheet vinyl soon after installation? I use to be a huge advocate for the 1/4" plywood under sheet vinyl, but stopped reccommending it after I had three of my own jobs go bad and heard many other reports from local shops and installers alike who were experiencing the same thing.

I know how easy this can be written off as installer error, but after a great amout of questions and research, to make a very long story short, I found out that the only way the plywood manufacturers warranty the installation is if you DO NOT patch the underlayment joints. It's tough for me be believe that they could make a plywood underlayment specifically for sheet vinyl installation, but not allow patching on the joints. (I am specifically referring to the Multiply 1/4" underlayment, as that is the only "professional grade" plywood available in my area)

As I'm sure you know, not patching the joints, unless it's an absolutley perfect installation with no gaps of any kind, is a perfect way to have the joints telegraph through. All they say is needed is to lightly sand the seams, which is great for the minor level indifferences from one sheet to another, but does nothing for gaps big or small. Anyone who's installed underlayment knows it's not possible to be COMPLETELY gap free all of the time..... maybe when they start building houses completely square.

I know there are several other factors that could have contributed to the jobs that failed, but they were all installed over sturdy existing substrates, ie, no movement in the existing floor before installing the wood, and the patch that I patch joints with (webcrete 95) is always thick enough that it won't even run off my trowel. Anyway, I explored all these and more as possibilities, but none made a difference in the ones that failed.

So has anyone ever heard of this happening before? I wonder if the area I live in (climate) could have anything to do with it? Possible I guess, except it's real dry here, not humid. I know all about allowing the sheets to acclimate to the room they're to be installed in, as well as room temperature and humidity, so none of those were factors. Also, I've seen this problem with Luan plywood and the regular 8x4 sanded sheets you get at home depot too, so it's not just a Multiply thing.......... I'd be very interested to get another professionals opinion on this.

Old 11-17-02, 07:07 PM
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Think about this...

The moisture in your patch, is swelling the seam edges in the plys!

Once moisture is introduced it may not swell immediately but give it a month or two,

Ever thought about perimeter gluing everything???
I don't install vinyl anymore due to lack of profits. but others that do and do it well swear they will never full spread a vinyl job again.

Check out this installers forum and message board.


Cut & paste to your browser and hit enter
Old 11-17-02, 08:07 PM
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I use a Artic Birch product, and have had great results. No call backs after about 5 pallets. I sand the joints, (taking care to do the same to the subfloor prior to installing it) and make sure the patching compound is dry before installing the vinyl. How do I know the patch is dry? A moisture meter.
Old 11-17-02, 11:53 PM
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Thanks for the input guys. I know (now) that it was the moisture in the patch that caused the peaking, not at the time of course, but it's only plywood that this happens with, never once has it ever happened with particle board. I know PB is the worst underlayment for several reasons, but at least I can patch the joints. I've always known I needed to be careful about too much moisture in my patch, that's why I said I mix it so it doesn't even run of my trowel. It's a pain in the butt to spread when it's that thick, and it dries too fast on me sometimes, but I know you can't be getting too much moisture into those joints. I did it the same on the joints that peaked, but it didn't seem to make a difference.

I am positive my patch is dry before I install the material, because I use a moisture meter as well.

Perimiter glueing felt back products??? Doesn't that void the warranty? What happens a year or so later when they need a patch put in from a knife or dining chair gouge or something? That's why I hate perimiter glue products to begin with. I like installing them, but the floor's pretty much ruined if a repair is ever needed. True, any small gaps in the underlayment wouldn't telegraph through if it were only glued at the perimiter, but I think that's too big a corner to be cutting.

I guess what I still want to know is when you guys install the plywood, do you patch the joints? I will look into the Artic Birch product and see if it's available here in my area. I love plywood underlayment for it's durability and lightweight install, (especially since PB is really the only other viable alternative) but it's got to be something I can patch.

Thanks again for the input!!

Old 11-18-02, 11:08 AM
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Check out Mannington's Spec for what they call their Options back. I've used this method with great success.
As to the underlayment, I take time to get all my edges flush and level. I made a little jig to allow me to make dead straight rips with my circular saw, which makes this a simple task. I "lightly butt" all the joints, then sand level. On the perimeter jobs no fill. Full spread depends on the materials, lighting, gloss level of material etc. Most of the time, no, but when in doubt, I hit them with patch, mixed with 50-50 ratio of latex to water. Works for me.

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