1/4" Hardibacker over particleboard subfloor

[loppert]

We're installing tile in a kitchen/dining area over a 3/4" particleboard subfloor. The house was built in the early 80's. I'm having a "discussion" with my tile guy over whether to use screws or nails on the 1/4" Hardibacker. The manufacturer has specs for both, but I was curious as to the experience of some of the folks here.

Thanks,

Lee

[JazMan]

Re: 1/4" Hardibacker over particleboard subfloor

Hi Lee,

You are not going to like the correct answer to your question. The particleboard should be removed and replaced with a suitable subfloor, such as 3/4" ext. t&g plywood. Particleboard is too unstable for the purpose. One reason you don't see it used as a subfloor today.

And that's the way it is!

Jaz

[loppert]

Re: 1/4" Hardibacker over particleboard subfloor

I wondered about that. The Hardie specs say "For all floors: Use minimum 5/8" exterior grade plywood or 23/32" exterior grade OSB, complying with local building codes and ANSI A108.11. Joists’ spacing not to exceed a maximum of 19.2" on center."

As I'm looking at the Hardie specs and recommendations from various tile sources, I see that there's a lot more to it than we've gotten into here, such as the levelness of the floor and the bed into which the Hardibacker is placed, to name a couple.

Before going further, a little background on me so that you'll know where I'm coming from.

I was downsized out of IT in 2003 at the age of 53. I have been a student of building/remodeling for many years, and figured that I could create a business that does it "the right way". I'm doing that, and I realize that the learning curve is steep.

My original thought was to create a business, and then find people with the knowledge to do it right. It's hard to find folks who have the know knowledge and ethics demonstrated in these forums, so I'm educating myself as we do the various projects we undertake.

I'm constantly getting into it with the guys who work for me, although I'm learning how to do that civilly. The issues generally center around whether "practical" knowledge outweighs "book" knowledge. Sometimes it does, but since my name's on the line with each job, I demand that we be better than code (we have no arguments over that), and that we comply with manufacturers' specifications (which we do have arguments over).

I've spent a lot of time digesting the information from these forums and other sources, and have a tremendous respect for the value of experience, which I'm just now getting.

My goal is to constantly upgrade my company's level of professionalism so that we become respected as folks who know what we're doing. I'm gradually doing that through a combination of self education and hiring people who do know what's what. I need to know enough to weed through the maze of BS that's out there to do that, which is generally why I post questions here.

Now, back to our regularly scheduled program:

I'll make an attempt to sell the HO on reworking the subfloor, and will provide a written disclaimer to him should he not go for it. We're committed, the old tile is up, and the kitchen is totally demo'd - plumber is coming in next week to rough in the new fixtures, etc.

Michael's book seems to be the definitive source, so I'll need to pick that up pretty soon, unless someone has a different, more appropriate suggestion.

Let's assume for the moment that our subfloor complies with the Hardie spec - which it may or may not. I know that it's more than 1/8" out of level.

Back to the original question, again based on your experience - nails or screws?

Second Question. I'm sure that tile setters are constantly faced with the same kind of floor we're dealing with here, and that you can't always get the HO to buy into a new subfloor. This is not a terrible floor, by the way - I'd say it's about average for what it is - a 25 year old ranch over a full basement. Do you put down SLC and work with what you have, walk away from the job, do it with a written disclaimer, or what?

Long post - sorry - just trying to get the conversation going.

Lee

[Robert Z]

Re: 1/4" Hardibacker over particleboard subfloor

Lee

Particle board is great for sticking laminates to it, but it is lousy for holding fasteners. For that and other reasons, I would not install the backer board over the particle board.

A "disclaimer" might or might not protect you from liability. There isn't a single tile related product that I know of that OK's the use of their product over OSB. You won't get any help from that source if you end up with a problem in this floor. I 've had various people, both attorneys and non-attorneys who are experienced in the business) tell me this.

The only thing I would consider doing with this floor (other than tearing the PB out) is to install minimum 1/2" BC or AC plywood over it with full spread glue, then install a membrane such as Noble TS, Laticrete Isomat, or Schluter Ditra) over the plywood. This assumes the joist situation is otherwise suitable for tile.

Even then, the problems with the fastener holding abilty of PB makes the second overlay difficult to secure to the subfloor. Current best practice in the tile industry says to secure an underlayment to the subfloor only, with no fasteners penetrating into the joists.

[loppert]

Re: 1/4" Hardibacker over particleboard subfloor

Jaz/Robert:

Thanks for the advice, and for giving me an alternative. My gut is that the extra 1/2" will be unacceptable to the HO from a floor height stand point, so I'll be pitching a new, level subfloor. The bad thing is that he's gone til next Wed - don't know if I'll be able to get in touch with him. We'll see.

Thanks again,

Lee

[loppert]

Re: 1/4" Hardibacker over particleboard subfloor

The Hardie specs say "For all floors: Use minimum 5/8" exterior grade plywood or 23/32" exterior grade OSB, complying with local building codes and ANSI A108.11. Joists’ spacing not to exceed a maximum of 19.2" on center."

Hardie seems to be okay with OSB, but they don't say anything about particleboard, and it's clear why that is. Given a choice, I wouldn't use anything but plywood, which is what I'll recommend to the HO (3/4", not 5/8").

The tile that was there looked to be 10-15 years old, and had a thin (1/4") underlayment. I didn't look that closely at it, but it appeared to be a gypsum product. It was nailed down with standard nails (not galvanized). There were no visible problems with it or anything below it, save a little settling toward the middle of the house (<1").

I presume that this is a common scenario for you guys that lay tile every day, since a fair # of homes from the 70's/80's had particle board subfloors. I'm wrestling with what to do if the HO doesn't want to replace the particleboard. Then I either eat the cost of plywood (3/4" on the bottom or 1/2" the top), live with the potential liability resulting from not replacing the particleboard, or worse yet, get failed by an astute inspector (it's a permitted job) and eat the whole thing.

Interesting - I'm open to suggestions, but it sounds like I don't have a lot of choices here.

BTW - The same client wants us to put down about 700 sf of Rosewood floors next year, which will most likely bring up the same issue, because I think we're looking at a nail down floor.

Lee

[MKEfird]

Re: 1/4&quot; Hardibacker over particleboard subfloor

I had better not ever see one piece of particle board on my job site. My opinion and everybody has one is that pb has very very limited uses in todays building industry other than burning in a woodstove.If you have it remove it.

Mark Efird
Traditional Hardwoods & Mouldings

[mbyrne]

Re: 1/4&quot; Hardibacker over particleboard subfloor

To one layer of particle board add anything wet: for example, thinset mortar. what happens? #1 Person decides to disregard ALL EVIDENCE THAT SAYS PARTICLE BOARD IS WORTH LESS THAN DOG DOO ON THE BOTTOM OF YOUR SHOES. #2 Wood fibers swell IN CONTACT WITH WET THINSET. #3 Floor lifts with swelling, #4 thinset dries, #5 Wood fibers dry but do not contract leaving particle board full of voids and weak spots. #5 Person walks on tiles set over ruined particle board. #6 Person sees cracked tiles and grout. #7 Person sues thinset manufacturer.

Loppert, you make the mistake of asuming that everybody in the construction business is aware of latest specs, instructions, guidelines, etc. I am here to tell you that only %5 of the people in construction consistently do a job that is up to spec--the rest just get by.

Particle board has been on the sh*t list for tile for almost as long as particle board has been made. Particle board does not have the OK to use by any known thinset manufacturer. Particle board has been listed as a sh*t material in both the ANSI A108 specs and the TCA Handbook.

This thread is closed.

[Martha Nelson]

I am installing a tub over particle board using deck mud to stabilize. I cant decide if I should paint with gardz or redguard prior to deck mud. I know particle board is not optimal, but it has lasted 41 years in a bathroom...last 20 covered by glued together laminate or tub so pretty protected. Laminate looks good too but I a replacing the tub and want to go with rigid core vinyl flooring.