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Unread 01-22-2019, 04:32 PM   #1
Lazarus
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Treatise on Greenboard

OK, OK.. I know that "Greenboard" has not been code for over two decades....but here is a good talk on why....


Greenboard is the pejorative term for a type of drywall that is used for walls in damp areas. Experts and industry professionals debate whether greenboard should be used in high-moisture areas. Some believe that cement board such as Durock is best used for tile in highly wet applications such as shower stalls, with greenboard and other water resistant drywall panels kept only to damp or dry areas.

Others believe that water resistant drywall is an effective base material for walls in even the wetter places.

Greenboard's paper facing alone does not inhibit mold growth. It must be treated with mold-resisting agents. Greenboard is still manufactured and sold, but it is slowly being supplanted by paperless drywall that resists moisture and can be used in either dry or moisture conditions.

Greenboard vs. Conventional Drywall
Greenboard's inner core of gypsum is the same as regular drywall. Also just like normal drywall, greenboard is attached directly to the studs.

Two things about the outer covering of greenboard differentiate it from conventional drywall:

Greenboard's outer paper covering resists water but is not considered to be waterproof. Some greenboard is impregnated with compounds that deter the growth of mold.
Greenboard's paper cover is a sea-foam green on one side. The color imparts no special water-resisting properties, but it does serve two purposes. For one, it identifies this as water-resistant drywall. For another, it helps the installer better see where he is applying the drywall compound.
Even without mold-resisting additives, the gypsum core of greenboard, like conventional drywall, does not support the growth of mold as it is not an organic product.

Greenboard and Water Resistant Drywall Dimensions
Greenboard drywall comes in 1/2-inch and 5/8-inch thicknesses and conventional 4-foot by 8-foot sizes.

The term greenboard is not official and is infrequently seen in company literature or at retailers. Instead, look for drywall advertised as being mold resistant or water resistant.

Even though greenboard drywall is the same thickness (5/8-inch) as Type X, it should not be confused with the fire-resistant product named Type X. Type X should be used in areas such as kitchens where a fire might be expected. Type X drywall is required by building code for garages.

Greenboard and Water Resistant Drywall Brands
Greenboard is found under such brand names as GP's ToughRock Mold-Guard Drywall Panel and American Gypsum's Aquabloc. Greenboard costs slightly more than conventional drywall.

Is Greenboard Allowed for Wet Applications?
Technically, greenboard and other water resistant drywall panels can be used in highly wet places. According to ASTM C 1396, Section 7, water-resistant drywall can be used in wet locations such as behind tile in bathtub or shower stalls. While greenboard drywall's paper covering is water-resistant, it is not waterproof. According to ASTM C473, after two hours of water immersion, the average water absorption for panels should not be more than 5-percent by weight.

Caution should be taken when using greenboard and other water resistant drywall panels for ceiling applications.

Ceiling panels can sag when subjected to high humidity conditions or to textures and finishing materials that contain moisture.

Water Resistant Drywall vs. Cement Board
Cement-based backerboards Durock, Wonderboard, and Hardibacker are all mineral-based, or cementitious, materials. Cement board is perfect for tile-covered wet applications like showers and tub surrounds. Wet or dry, such backerboard provides a stable base for tiling. Cement board will never biodegrade because it has no organic materials. The organic element to drywall's paper is the chief reason why drywall may experience mold and mildew. Another advantage of cement board is that it can be used as a base for tile flooring; drywall of any type can never be used for flooring applications.

One reason why builders may use greenboard for highly wet areas, though, is because it is faster and easier to install and less expensive on a square-foot basis.

It is best to use greenboard or other water resistant drywall in the large areas of bathrooms, kitchens, and other areas where the drywall may be subjected to lightly damp conditions, humidity, and the occasional minor splashes of water. Using greenboard drywall in a highly wet location is possible but cementitious materials are a better product for that location. At the least, severe mold growth will occur with drywall. Sag and outright failure may occur when the drywall has been subjected to an abundance of water.

Greenboard and Water Resistant Drywall Uses and Locations
Location Use or Not?
Shower stall walls No
Bathtub enclosure, tiled No
Bathtub enclosure, pre-fabricated Yes
Water-prone basement walls No
Basement areas other than bathing facilities Yes
Saunas and steam rooms No
Kitchen, near sink Either
Garage No
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Unread 01-22-2019, 06:57 PM   #2
cx
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It would be nice to have a date and a proper attribution for that piece, Laz.

Don't think I can agree at all that it is a "good talk" on the subject.
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Unread 01-23-2019, 07:54 AM   #3
speed51133
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what exactly is the additive on greenboard that makes it different? I was under the impression it is simply wax. also, greenboard is just a generic name. company X's formulation can be totally different than company y's. there is no code or standard to which greenboard needs to meet to be called greenboard.

also, I thought the new school of thought was that greenboard is basically garbage. It costs more and does not offer any added protection. For this reason, don't even bother using it anywhere at all.

the above is all just what I have "heard". no idea how truthful it is.....
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Unread 01-23-2019, 08:48 AM   #4
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Sorry, was sent to me without a link. I'll see if I can run it down.....
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Unread 01-23-2019, 08:49 AM   #5
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The article is either old or the writer is misinformed.
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Unread 01-23-2019, 09:17 AM   #6
Lazarus
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Here is the source, updated 8/14/18.

https://www.thespruce.com/what-is-gr...rywall-1822831

Dave, just curious about the inaccuracies in the article. Don't want to mislead any client asking about the product....
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Unread 01-23-2019, 10:31 AM   #7
tilemanct
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Oh builders and uninformed tile setters please keep using that ol green board in wet areas. It's going to be paying the mortgage on the Florida condo we want to buy!!
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Unread 01-24-2019, 09:53 AM   #8
Dave Gobis
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Laz, rather than ignore you because it is too much work I will respond. It would take a substantial investment of time and effort to accurately address all the issues in that article and include the relevant cites. In the end he says don't do it. I have grown increasingly frustrated with the plethora of misinformation being spread in our and other trades, it has started to take the fun out of it for me. Sales Reps are a disportionate ever increasing part of this. My soap box is put away, I am retired. Time for the next generation to hit the books, make the observations, do the testing and make the results available. Thinking Spring yard projects myself.
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Unread 01-24-2019, 10:54 AM   #9
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Heh, I started down the tile and waterproofing rabbit hole as an HO that just knew cement board was proper for showers, nothing about anything else. The contractor my mom hired used Greenboard on a plastic tub surround and still managed to mess it up (don't ask...)

I kind of want to (as I often ask here...) play devil's advocate/stir the pot a bit about Greenboard. Firstly, I feel a problem with Greenboard is there seems to be a lot of variance between types of Greenboard. The stuff I demo'd from my bathroom was LaFarge brand, and was heavy and seemed to sponge water up and turned to mush like normal drywall after a few rainstorms left on my back porch. I bought some USG Ultralight Green Board and decided to leave a few scraps to the porch test, and it was out a whole month and still solid, no delamination, and had zero mold. Further, I tested some scraps fully submerged, and it would stay solid for 1-2 days fully submerged, but would turn to mush in a week of full immersion. So this leads me to believe there's likely wildly varying quality within brands of MR drywall, whereas cement board just by nature of the material and very little competition nobody can really cheat and make an awful one. Thinking logically, they make working gypsum exterior sheathing, so working MR drywall doesn't seem impossible.

The other thing is, in other countries companies 100% approve of using liquid waterproofers over greenboard as long as you use the tape and do it correctly, and it's 100% the norm and seemingly failures aren't happening with liquid waterproofed "tanked" bathrooms (in UK liquid waterproofers are sold with the tape and called tanking kits...)

https://www.youtube.com/watch?v=qT430p-hu-o
This official Mapei video from Hungary has someone applying liquid waterproofer to green board.

https://www.youtube.com/watch?v=aHPMInq1SGQ
This UK video too, over drywall.

I'm not arguing it's the best way 100%, but would I trust taped liquid waterproofed greenboard over no vapor barrier, no tape Hardiebacker/Durock installs that seem ridiculously common nowadays? You bet. What I think was, failures if done wrong with green board take weeks or under a year to show up, whereas with cement board you could potentially maybe get away with still doing things wrong but having the failures happen later/get away with more wrong. I don't know all the code stuff one way or the other, but I think cement boards allow people to basically be more stupid and do more stuff wrong.

Not a pro tiler, but it's just my opinion that it's not automatically bad stuff. The sagging issue in this article I actually had with LaFarge (my ceiling probably would have collapsed in a few years) because the LaFarge stuff was heavy. The USG Ultralite is actually spec'd in the data sheet as fine for ceilings, even over 24" joists without sagging if it's the right direction. The older LaFarge stuff I pulled out was a lot heavier than normal drywall sheets.

For the record, in my own bathroom I was so OCD/crazy I used cement boards on all the walls except one small section section and the ceiling where I used 5/8" drywall, and then did a two coat veneer plaster system on top of the cement board everywhere there wasn't tile (tub surround and floor.) I was that paranoid about mold potential and water damage and kind of wanted to overbuild for the hell of it. Looking back I'd have done a single coat veneer plaster over the USG Ultralight green board and been done (and still would have used Wonderboard and Aquadefense under the tiles...)
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Unread 01-24-2019, 01:05 PM   #10
Lazarus
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Dave....Thanks for responding, even though I still can't pinpoint any issues that are incorrect or misinformed. Maybe someone else (Bueller??) can chime in on the subject.

I spent some time on the site and I can find no fault on the drywall advice given there...and I've done a bit of drywall hanging. I guess I assumed that their "take" on the greenboard subject was similarly accurate....but hey, I've been wrong before.......

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Unread 01-24-2019, 05:09 PM   #11
Raymond S
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Impossible to count the number of Greenboard showers and tub surrounds I’ve torn out. Complete mush on many of them, usually where the water constantly pounded or under the valves if they were leaking.
Came across quite a bit of the exterior gypsum stuff that had disintegrated to nothing, as well. That was in New Orleans after Katrina. I even phoned cx and spoke with him about it then.
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Unread 01-24-2019, 05:28 PM   #12
Lazarus
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I still haven't seen links or anything that approves greenboard for a shower install without the use of AquaDefense or Hydroban or any of the other waterproofing agents. Maybe CX can expand on how the article is in error?
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Unread 01-25-2019, 08:04 AM   #13
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Hey Dave..need any help with those spring yard projects? There are days I feel the same way...though a few more years till I can retire.
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Unread 01-25-2019, 10:14 AM   #14
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Laz, we have spent years discussing drywall issues in tech and standards but much less once the code was changed in 2006. Every drywall manufacture makes a backer board and the push to dump MR board came from them, they made the code presentation, I was there at the ICC meeting. Simply too much history to condense.

Dave, Help on yard projects is always welcome, especially since the ash borer has made itself at home. We cut down 50-100 trees a year and some still fall down because we have not got to them. Me and the wife cut 8 acres of grass a week too and with no trees the acreage grows. My latest post retirement project about an acre of annual wildflower planting. Winter is equipment servicing and repair.
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Unread 01-25-2019, 10:20 AM   #15
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