Glue down vinyl plank in a 1970's modular home

[AC2132]

Hello all,

I've got a 1978 modular home, on an above-ground concrete foundation (just around the perimeter with a sizeable crawl space under the house). I live in an extremely dry climate and the crawl space is well ventilated.

Anyway, since it is a modular home, it has a 1/2" plywood subfloor with a 1/2" particle board underlayment. Both of these layers go under every wall in the house and even under the doors. Knowing that particle board is far from the ideal underlayment, I wish I was in a position to remove it. But that is just not feasible. The particle board underlayment is in excellent condition (dry climate) with only a tiny bit of water damage near the sliding door from snowy feet over old carpet.

I'm planning to put down a glue down vinyl plank because of it's durability, (lack of) expense, and ease of installation. I considered a floating vinyl option, but I am bothered by those. The click together mechanisms seem to fail. I also considered sheet vinyl since it would not have seams like the individual planks, but it seems difficult to wrestle into place by myself and is difficult to repair if torn.

I'm sure this isn't the proper approach but my plan is to install 1/4" plywood underlayment over the top of the PB with staples long enough to sink into the plywood subfloor. But I have questions:

1. Do I need to level the surface of the PB underlayment before installing the 1/4" plywood? The floor is fairly flat with some deviation (maybe 1/16-1/4" over a 4 foot span).
2. How long do my staples need to be for the 1/4" underlayment? 1"? 1 1/8"?
3. Is there something else I should use to just seal the particle board and install the glue down vinyl directly to that? (The kitchen and bathrooms have originally installed linoleum still adhered to it with no problems.)

I know the particle board is bad. But that's just the reality of the situation I'm in. Thank you very much for your time.

 

[havasu]

I don't know why you would go thru the expense of sheeting, screwing, then gluing down, rather than just using a good quality click lock vinyl plank. I installed it in both my main home and my vacation mobile home, and have yet to have any problems.

 

[highup]

What havasu said is correct. The locking mechanisms can fail for two reasons. Buying a cheap, thin product and not making the floor flat. The floor needs to be flat do the joints don't flex up and down. Too many people ignore the flatness requirements.
Coretec and Provenza are two good products. Not cheap, but you get what you pay for. They are extremely durable and have great wear guarantees.
These floors also have a more quiet sound than a material glued directly to the floor. A high quality 1/4" plywood worthy of gluing to, will not be cheap. I'd rather spend the $1.40 per sq ft price of the plywood on the flooring. You won't need plywood with a floating floor, just flatten it to the manufacturers specs.

 

[AC2132]

Thanks to both of you. So you're saying that the 1/4" plywood underlayment from the big box stores at $0.50 per square foot is no good, eh?

I was planning to just put that stuff down and glue over it.

 

[highup]

Some place to sell 4 ft by 4 ft and there is also a 4 foot by 5 foot plywood made for underlayment.
I don't know where you live and what plywood prices are there. But around here I'm thinking around $45 per sheet from a lumber yard for AC grade plywood.
If you have a lumber yard nearby go take a look at their quarter inch AC grade plywood, then go take a look at the quarter inch plywood at the box stores that's sold as underlayment. The box stores sells material that looks more like a mahogany door skin if you know what that is. Their stuff usually has one thick center core and two paper thin layers on the top and bottom.
If you find a good flooring grade underlayment in 4-ft x 4-ft sheets, it will have as many as five layers and is nice material to work with and much stronger and more stable than the flimsy stuff you see at the box stores.
The stuff I've seen that some places sell as underlayment is less than one quarter inch thick. Not by much but maybe 1/32 thinner. You would need an extremely accurate stapler so that the staples don't go all the way through but also don't protrude out the top. That's hard to do with the cheap three layer material that sold at box stores. And don't forget that's a lot of staples. You're going to be putting a staple every two and a half inches along the seams and about four inches throughout the entire panel itself. You would not want to place Staples more than 5 in apart throughout the entire center of the board. The reason for this is thin boards need a lot of staples because a thin panel isn't as stable. This may seem extreme but think of it this way. Put in four for nails to hold down a sheet of poster board. With any humidity changes the poster board will warp quite easily. Now put four nails in the sheet of 3/4 inch plywood that's about the same size as the poster board.
All in all you need a lot of small fasteners to hold down the quarter inch plywood, but you need less and much stronger fasteners to hold down three quarter inch plywood.
Hope all of my ramblings aren't too confusing.

 

[AC2132]

Some place to sell 4 ft by 4 ft and there is also a 4 foot by 5 foot plywood made for underlayment.
I don't know where you live and what plywood prices are there. But around here I'm thinking around $45 per sheet from a lumber yard for AC grade plywood.
If you have a lumber yard nearby go take a look at their quarter inch AC grade plywood, then go take a look at the quarter inch plywood at the box stores that's sold as underlayment. The box stores sells material that looks more like a mahogany door skin if you know what that is. Their stuff usually has one thick center core and two paper thin layers on the top and bottom.
If you find a good flooring grade underlayment in 4-ft x 4-ft sheets, it will have as many as five layers and is nice material to work with and much stronger and more stable than the flimsy stuff you see at the box stores.
The stuff I've seen that some places sell as underlayment is less than one quarter inch thick. Not by much but maybe 1/32 thinner. You would need an extremely accurate stapler so that the staples don't go all the way through but also don't protrude out the top. That's hard to do with the cheap three layer material that sold at box stores. And don't forget that's a lot of staples. You're going to be putting a staple every two and a half inches along the seams and about four inches throughout the entire panel itself. You would not want to place Staples more than 5 in apart throughout the entire center of the board. The reason for this is thin boards need a lot of staples because a thin panel isn't as stable. This may seem extreme but think of it this way. Put in four for nails to hold down a sheet of poster board. With any humidity changes the poster board will warp quite easily. Now put four nails in the sheet of 3/4 inch plywood that's about the same size as the poster board.
All in all you need a lot of small fasteners to hold down the quarter inch plywood, but you need less and much stronger fasteners to hold down three quarter inch plywood.
Hope all of my ramblings aren't too confusing.

Thank you very much for this info and for your advice! That does make sense.

 

[Floorist]

Just remember, flat and level are two different things. The floor needs to be flat, level not so much.

 

[highup]

Worst place to find low spots in manufactured homes is the last 2 or 3 feet towards the outside walls. The manufactured home's frame stops about that point, so the last couple of feet isn't supported as well. In later modeled units, I'm used to seeing a 1/4" to 3/8" droop in the last two or three feet approaching an outside wall.
Like Rusty said, it's all about flat, not "level"