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scarymary 04-16-2010 08:56 AM

What is this?
1 Attachment(s)
Yesterday my brother decided to pull up a piece of the particle board in the living room, (which is a converted carport/garage) and found this underneath. The plan is to install laminate flooring over the entire floor including the stairs. Don't worry, I only have 3 steps down. My question is would I necessarily need to install a piece of thick moisture resistant plywood on top of this before laying the laminate or can I get by with something not quite as expensive or thick as 3/4 inch plywood, but just as durable and acceptable for putting down the laminate flooring? These planks run all the way over the room. Actually I fully expected to see just 2x4s laid flat underneath the particle board on top of the concrete, but not the case. It looks like cedar planks to me, but I could be wrong.

Attachment 1831

Nestor_Kelebay 04-16-2010 10:19 AM

Those are fir 1X6's I think (judging by the wood grain pattern).

If that is a converted carport/garage, then someone must have built a wood floor over the concrete garage pad (for a warmer floor). No one would have built a wood floor expecting to park a car on it.

Before you cover that up, I would inspect the ends of the floorboards carefully to see if they've been cut. It doesn't look so from the photo. Those floor boards aren't perfectly flat, so anyone cutting through the particle board with a circular saw after it was installed would have left kerf marks in the particle board and would have scored the crests of the floor boards. It looks to me that the underlayment (the particle board) was just nailed down with a piece missing, and a small piece of particle board was put in to fill in that spot. Your brother pryed up that small piece.

You can just nail down a new piece of particle board of the same thickness.

But, if it were me, I would pull up ALL of that particle board and nail down plywood underlayment instead. The difference between plywood and plywood underlayment is that plywood is allowed to have voids in the inner plies. These voids would cause problems ("soft spots") on a floor, and so any voids in plywood underlayment have to be smaller than a certain size or filled with a filling material.

The difference between plywood and particle board underlayment is that getting wet won't harm plywood underlayment. If particle board underlayment gets wet, it swells up and gets soft. They only used particle board as underlayment because it was cheap. Fir plywood underlayment is much more durable than particle board underlayment, and you wouldn't have to worry about any large water spills wrecking the underlayment.

scarymary 04-16-2010 10:31 AM

Actually, the particle board covers all of that plank style that you see in the picture. There was carpet on top of that. We have removed all of the carpet. What I'm driving at here is would we necessarily need to put something of a thickness of 3/4" plywood or could we go with something thinner over the top of that plank that you see in the pic? Oh, and there are some type of joists underneath those planks there in the picture. They are nailed to something.

Nestor_Kelebay 04-16-2010 04:06 PM


Thinner. You should put the same thickness of material down over those planks as the piece you removed. That looks to be about 3/8 inch thickness approximately. So you would use whatever thickness of material that that you took out because that would result in the floor over the planks being flush and level with the surrounding floor.

If someone told you that you need to nail down 3/4 inch plywood over those planks, they simply didn't understand the situation.

You should understand that it's those planks that provide all the strength to your floor. The "underlayment" that you removed (and now need to replace) doesn't provide any strength. It's just there to provide a smooth surface over which to install the final flooring material.

You don't need to know the rest:

Normally when the build a house, they have floor joists which are supported by concrete walls of the house's basement. Over top of the floor joists they will nail down 1X6 plank or 3/4 inch fir plywood, and that layer of planks or plywood is called the "SUBFLOOR". Then the 2X6 exterior walls and 2X4 interior walls of the house are built on top of the subfloor. If the subfloor consists of planks, as it does in your case, the planks will be nailed down at an angle to the joists because doing so results in a more rigid construction than nailing them perpendicular to the joists.

Then, they would normally nail down something called "UNDERLAYMENT" inside each "room" of the house to provide a smooth surface to install the flooring over. In your case, you have particle board underlayment.
One of the benefits of installing plywood underlayment over a plywood subfloor (for example) is that if you ever want to remove flooring that is glued down, like sheet vinyl or carpet, you can pry the underlayment up with the flooring still glued to it, and then put down new underlayment to install the new flooring over. That would save a great deal of work trying to remove the old flooring.

scarymary 04-17-2010 09:32 AM

This is a converted carport. There are joists under the planks there in the picture which are somehow, I am assuming, attached to the concrete floor of the previous carport/garage. The particle board we removed from the floor was 5/8". We measured it yesterday. We will probably remove the rest of the particle board today.

Nestor_Kelebay 04-17-2010 12:42 PM


Originally Posted by scarymary (Post 43692)
This is a converted carport. There are joists under the planks there in the picture which are somehow, I am assuming, attached to the concrete floor of the previous carport/garage. The particle board we removed from the floor was 5/8". We measured it yesterday. We will probably remove the rest of the particle board today.

Replacing the particle board underlayment with plywood underlayment is a good idea. Particle board swells up and gets soft if it gets wet. The only reason particle board was used as an underlayment was because it was inexpensive. It's really not a good product to use for anything.

Normally underlayment is meant to be thin, typically 3/8 inch in thickness or less. It's not necessary to use the same thickness of underlayment, but you may have to remove the baseboards from the walls and raise or lower them if you use a different thickness of underlayment. Riverside Wood Products here in Manitoba makes a 5/16 inch fir plywood underlayment which you can double up to make 5/8 of an inch.

scarymary 04-18-2010 08:20 AM

My husband and I looked around at Lowes yesterday, but we didn't see any subfloor/underlayment material of 5/8" thickness. I wonder how much difference it would make to use something thicker than that.........

Bud Cline 04-18-2010 10:37 AM

The thicker the better. You are asking for trouble covering those boards when you could replace them with a more suitable plywood. Those boards will expand and contract and move around. Notice how some are cupped and some are crowned now. You wouldn't notice it under carpet but you will notice it under a hard surface flooring. You'll never keep the seams together in the finished flooring especially if you use one of those cheap "click" laminates that are being sold today.

Get rid of those boards.

Sorry Nestor but your research has yielded you some erroneous information.

Underlayment plywood's are available in many thicknesses for various reasons. Underlayments ARE NOT meant to be thin, that is ridiculous.

Remove those boards and use a 3/4" Exposure 1 "Underlayment" product and you'll be fine.

And YES...the particle board was a mistake from the git-go.:)

Nestor_Kelebay 04-18-2010 11:24 AM

I would never remove the plank subfloor to replace it with plywood.

I would replace the particle board underlayment with fir plywood underlayment, and I would put that new underlayment over the plank subfloor.

Take your picture down to any of the flooring stores in your area and ask to talk to the Installations Manager. In my view there's nothing wrong with your existing plank subfloor, and there is absolutely no reason to replace those planks with 3/4 inch plywood. Speak to the Installation Manager at several flooring stores and see if they agree that the subfloor needs to be replace. I very much doubt they would.

Bud Cline 04-18-2010 11:31 AM

Dimensional lumber in that form is unstable. It expands and contracts routinely to say nothing of the concaving and convexing going on with seasonal changes.

The way to stabilize it is to cover it with plywood but even then the plywood install would be rickety rackety because of the condition of the boards. Now is the time to remedy any future problems.

Seams in laminate flooring won't stay together when the substrate is changing form a couple of times per year. Get rid of that junk while the opportunity has presented itself. It will make good fire wood.:)

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