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eyeglass 11-12-2010 05:47 PM

underlayment materials for vinyl sheet flooring in bathroom
What materials can I uses as an underlayment for a bathroom vinyl flooring.
My brother said to use Masonite and I said use 3/8" plywood?
Which is correct and what thickness the materials should be?
What thickness is Masonite?
If Masonite is uses, do I turn the smooth side face up?
Is 3/8" plywood is not as good as material to use as a subfloor?

oh'mike 11-12-2010 06:11 PM

There are several 1/4" hardwood plys with water resistant glues made for underlayment--
Do not use masonite--it puffs up with any moisture--3/8 ab would work,however I would use the hardwood ply designed for the job.

In this area Multi-Ply is a common brand.

Jim has pictures of a typical bath underlayment job here-Jim's Downstairs Bathroom Project - Page 5 - DIY Chatroom - DIY Home Improvement Forum

rusty baker 11-12-2010 07:20 PM

Masonite is a really bad idea, but when it was used 30 some odd years ago, the rough side went up. 1/4 multiply or any good birch plywood. Rememder it needs to be stapled every 4" in the field and every 1-2" on the edges. It takes a 1/4" crown staple 9/16" long. Do not use screws, they make the plywood pucker.

Anti-wingnut 11-12-2010 07:30 PM

Listen to Rusty, he knows his stuff. Commercial standard is 1/4" underlayment (zero void) AC plywood. Should be less than $25/sheet

eyeglass 11-13-2010 10:44 AM

Rusty: I have a installer coming in to do the work for me, he suppose to have 30 years experience. Do you think he will lean toward using Masonite? So you think its a water moisture problem? Original underlayment(3/8") was partical boardwith vinyl sheeting.We never have any moisture problem with water for last 40 years, so do you think he can use Masonite? How thick is Masonite come in?.
You also recommended plywood. Is it Expoure I 3/8" A-C Plywood ?
Which side up if I use this A-C Plywood?

rusty baker 11-13-2010 11:13 AM

Masonite will void all warranties and will not last, it swells up and comes apart with moisture, Why do you want to use an unapproved underlayment? Why not just use 1/4" underlayment plywood, like you are supposed to use?

Anti-wingnut 11-13-2010 11:29 AM

I have about 30 years of construction experience also, the last 12 as a superintendent on Class A commercial remodels.

Do not use Masonite. Any installer worth a damn would run away from a job on top of Masonite. If I saw any one using Masonite for that purpose on any of my jobs, they would be thrown into the street.

Your choices are:
1) Go on top of the existing
Pro's: cheap
Cons: Possible poor adhesion, telegraphing of underlying surface features

2) Remove existing sheet vinyl, prep floor with leveling compound, and sand to a smooth finish
Pro's: Does not add height
Con's: Labor intensive. Time intensive. Difficult to do correctly, high chance of shoddy work

3) Remove all existing materials to subfloor, and replace with new underlayment.
Pro's: Existing elevations are maintained. Very good surface results
Con's: Difficult, pricey, difficult to cut at cabinets

4) Remove existing vinyl and install new underlayment. Use underlayment grade AC plywood.
Pro's: Very good surface
Con's: Added height

I suggest that you visit the web sites of several manufacturers. Most do not recommend installation over particle board, OSB, or non-underlayment grade plywood. The use of Masonite as an underlayment dates to the dinosaurs, and ended shortly thereafter. Any reputable flooring installer will require 1/4" underlayment grade AC.

Not all AC is underlayment grade. As far as I know, only 1/4" comes in underlayment grade. We have used 5/8" AC in fast food restaurants where we needed more height, and in seven years, there has not been a problem. But I would not recommend this.

eyeglass 11-15-2010 02:27 PM

Thanks to you both: The installer said he would use partical board since the entire sheet vinyl unerlayment of the house is 3/8" partical board. I know you all do not like this idea too, but my brother said he spend too much money on the shower and the Utility Room, he beleive this will work since he never have any rotten floor from water damages in his 40 years. The only reason he changing the bathroom flooring is because the shower contrctor ripped out the entire underlayment off when he did the shower area. The bathroom will be lay with commerical vinyl sheeting (thicker)with coved edges.

rusty baker 11-15-2010 03:21 PM

Particle board is a mistake Even the moisture from the adhesive can ruin it. If the installer uses particle board, he is not a professional. It will void all warranties.

rusty baker 11-15-2010 03:48 PM

I don't understand why people come on here for advice when they intend to do a job wrong anyway. :(

Anti-wingnut 11-15-2010 06:16 PM

I ditto what Rusty said. You also have to look at the real cost. Partical board will run about $12/sheet. Underlayment grade 1/4"AC will be about $22/sheet. Labor will be equal. For $30 saved, you will void the warranty and ignore manufacturers recommendations.

You say this floor is coved. Do you mean rubber cove base, or coved vinyl? Coved vinyl is a high skill job, and any installer who says he can cove vinyl, yet will use partical board is lying to you.

eyeglass 11-16-2010 07:14 PM

FYI: The guy just finish the job according to my brother. He did cove it , he use a hot looking iron instrument that help form the curve of the thick commerical vinyl sheet.

rusty baker 11-16-2010 07:18 PM

I hope he didn't use particle board.:censored:

MStedman 12-05-2013 06:33 AM

..on concrete foundation floor?
Hey there folks. I came across this thread while trying to find a way to level my bathroom floor (concrete) prior to putting down the vinyl.

I have some vinyl to lay down but I realized the floor is too unlevel to be comfortable. I pulled up old vinyl (20 years old - the vinyl, not me) and don't recall any leveling problems but in placing the new vinyl down for a dry fit I noticed that some leveling will be necessary.

Using any wood based underlayment is fine but how do I attach it to the concrete? The thought of drilling a bunch of holes in the concrete is not a pleasant thought. Is there an adhesive recommended for wood (not particle board since it's a bathroom)?

Thanks for any direction you can provide.


Seattle2k 12-09-2013 02:02 PM

@MStedman - you'll need to put down self-leveling compound first. The vinyl will install on top of that.

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