Green Board or Durock?

[goeduck]

I have a rental that I bought a year and a half ago that has had a nagging mold problem in the shower ceiling. The previous owner did a partial DIY reroof which created leaks above the master bedroom and bath when the wind blew which may have been contributing to the problem. I hired a roofer to re-roof that area and that did fix a leak in the bedroom, so I have to believe there are no leaks above the bathroom, although the bath is way up against the eave and very hard to get at to be 100% positive. After the roofing, I waited a month and bleached, put on a mold killer, mold primer and painted with a mold resistant paint. Two months later the mold is showing through. The tenant is great, but they are military and very detail oriented. So the slight mold bugs them. I want to put an end to the problem and plan to replace the ceiling drywall. The house is vintage 1950, so it probably has regular sheetrock on the ceiling. My question to all is should I use green board, Durock or some other alternative if I want to completely get rid of the problem forever. It is just a standard full bath, so material cost difference is minor.

 

[ultrarunner]

I don’t think it’s a underlying board problem if both start mildew free.

I use cultured marble for bath and shower surrounds… leak proof and easy clean up.

Also for ceilings over showers.

For painted surfaces Zinsser Perma-White with Zinsser Mold Killing Primer is a one two punch.

These products have eliminated mold issues in my rentals.

Of course ventilation such as a exhaust fan is great if used.

Same treatment for exterior wall closets because many renters stuff closets so tight air can’t circulate.

At $45 a gallon it’s not cheap but does the job.

 

[Midniteoyl]

Did you replace the sheetrock or just bleach and paint?

Pull the sheetrock and clean/bleach the area of the attic/roof above it, then re-sheet with Greenboard. You should probably do at least part way down the wall as well.

Also, do you have a good bathroom fan that is not blocked or just blowing into the attic? It should blow all the way to through an outside wall, not a roof vent that can leak.

Since you had a leak or 2 for awhile, you should also look at the attic and underside of the roof for any other damage and mold.

 

[goeduck]

For painted surfaces Zinsser Perma-White with Zinsser Mold Killing Primer is a one two punch.

These products have eliminated mold issues in my rentals.

That is the primer that I used, but I used a Benjamin Moore mold resistant paint. Good to know about Zinsser Perma-White.

 

[ultrarunner]

That is the primer that I used, but I used a Benjamon Moore mold resistant paint. Good to know

That is the primer that I used, but I used a Benjamin Moore mold resistant paint. Good to know about Zinsser Perma-White.

I had reoccurring issues in rentals which can become a big problem depending on resident lifestyle.

Started using 2 coats perma white 40 years ago… they even have an exterior paint but could not get it easily in California…

I’m hoping the formula hasn’t changed.

I have done entire rentals with it for insurance.

 

[goeduck]

Did you replace the sheetrock or just bleach and paint?

Pull the sheetrock and clean/bleach the area of the attic/roof above it, then re-sheet with Greenboard. You should probably do at least part way down the wall as well.

Also, do you have a good bathroom fan that is not blocked or just blowing into the attic? It should blow all the way to through an outside wall, not a roof vent that can leak.

Since you had a leak or 2 for awhile, you should also look at the attic and underside of the roof for any other damage and mold.

I just bleached and painted, trying to save the effort of replacing the underlying board. The bath fan does blow out the gable vent. The underside of the roof looks fine but the top side of the sheetrock is somewhat grey. The previous owner roofed that area starting at the top and worked his way to the fascia for whatever reason. He also did the same thing with the tar paper. To do that he had to nail up high on the shingles and not on the nailing strip. So when the wind blew from the west (unusual in that area), the roofer identified a few shingle areas that he believed were lifting in the wind which would allow rain to blow under and then get between the shingles and tar paper. Since the wind rarely blew in that direction, the roof underside looks good, but the top of the sheetrock could have had moisture sitting on it for a while.

 

[ponytug]

@goeduck I see a couple of issues here.

Speaking as a former roofer, roofing from the top down is not a reasonable way to roof, and it is absolutely going to be prone to wind damage and water penetration. I think that you are likely playing roulette with the roof.

I don't know if the roof is the source of the problem, but it won't help the longevity of the house.

Overpainting surfaces that have had mold is tough, because the spores for molds are so tough. I use TSP and bleach, but for more than mild mold, I think it is a rip out and replace. While anti-mildew paint and additives help, I think it is asking a lot, and perhaps too much give where you are located.

If it were me, I would start would increasing the fan size, then remove the problematic sheetrock, and start over. You can get fans with humidity sensors that will continue to run u til the humidity drops below a set level. Given the history, I would certainly use a mildew resistant primer and paint if you go with sheetrock, but again, given the history, if it were me, I would go for an enclosed shower stall with 100% composite surfaces.

All the best,

Peter

 

[goeduck]

Speaking as a former roofer, roofing from the top down is not a reasonable way to roof, and it is absolutely going to be prone to wind damage and water penetration. I think that you are likely playing roulette with the roof.

The previous DIY owner did that, I had that area reroofed by a roofing contractor and he started at the bottom. Both my home inspector and I missed that that portion of the house was re-roofed when I bought it. I usually will not buy any house with significant DIY. I am guessing they had some damage from tree branches and were cutting corners on the repair.

I agree that ripping the old ceiling board out and replacing with new board is the way to go.

 

[ponytug]

The previous DIY owner did that, I had that are reroofed by a roofing contractor and he started at the top.

Wow. I've never seen that. What is the roofing material?

 

[goeduck]

Wow. I've never seen that. What is the roofing material?

Apparently I had a typo. I had that area reroofed by a roofing contractor and he started at the bottom.

 

[Midniteoyl]

Try to have that bath fan vent properly out the side wall. The gable vent is not the correct place for venting it as the moisture can still be pushed back into the attic and condense.

You can also tie it into the light switch so it's always on when the light is on. Better is to have an 'Off timer' so it will also keep running for 10-15mins after they leave the bathroom.

 

[ultrarunner]

Maybe a sensor would solve problems…

At rentals, just like smoke detectors disabled I have had bathroom fans disabled :-(

 

[Jstpssng]

Maybe a sensor would solve problems…

At rentals, just like smoke detectors disabled I have had bathroom fans disabled :-(

It's disabled at my house also, until I put it on a separate switch from the light.

 

[EddieWalker]

Mold is a plant, and it needs to be treated like an unwanted weed. Replacing the ceiling will get rid of what is growing there now, but it will just come back if you still have the same conditions.

To kill mold, I like to use Swimming Pool Liquid Shock. A gallon of it at Home Depot is just a few bucks, and it's in the outdoor garden area with pond and pool supplies. Put it in a spray gun and soak the area. This will kill the mold down to it's roots.

I'm also a big fan of Zinsser primer. In my experience, it's the only one that actually works.

Then I use exterior paint in bathrooms. Exterior paint is harder and seals better then interior paint. I don't think any of the mold blocking stuff does anything for interior paint. I buy paint from Sherwin Williams for most of my jobs, and usually get the more expensive stuff if my clients are willing to pay for it. Emerald Paint is probably the very best paint that you can buy.

To help prevent mold, the surface needs to be dry. Air flow is the very best way to keep everything dry. When I do a remodel for a client, I like to put the ceiling vent fan right at the entrance to the shower. Usually, it's close to the toilet too, but my main goal is to clear out the steam from the shower, so the ceiling remains dry.

To answer your question about what material is best to use for a ceiling in a bathroom, that would be the green Mold Guard sheetrock designed for moisture. But I would not replace the existing sheetrock unless it was damaged and needed to be replaced.

Most ceilings are 5/8's inches thick because the ceiling joists are 24 inches apart. It's not always done that way, and that's another issue, but if you have 5/8's sheetrock up there already, nothing else is going to have that thickness. If your ceiling joists are 16 inches apart, or less, half inch sheetrock can be used, or you can use something else.

The only reason to use something like GoBoard or Hardie on a ceiling is if you are going to tile the ceiling. And then you need to add lumber to the joists to get your span to 16 inches or less. I do mine at 12 inches when I tile a ceiling in a shower.

 

[goeduck]

Try to have that bath fan vent properly out the side wall. The gable vent is not the correct place for venting it as the moisture can still be pushed back into the attic and condense.

You can also tie it into the light switch so it's always on when the light is on. Better is to have an 'Off timer' so it will also keep running for 10-15mins after they leave the bathroom.

I used the wrong description, the fan does vent to outside. The dedicated vent is on the same attic wall as the gable vent.

 

[goeduck]

The replacement Mold Tough drywall is up. I see Zinsser has a paint/primer combination for indoor baths and kitchens, is that any good? I typically don't go for combo paint/primer. As far as exterior Zinsser mold resistant paint as mentioned goes, I found some for wood. Any advice on the actual primer and paint selections? The old drywall that the previous owner had installed was standard drywall and, as it turns out, the roof had been leaking prior to my re-roof over the worst area, the drywall had mold on top and bottom. Bath vent was fully functional to outside.

 

[paulsharvey]

So, you need to atleast access the back (top) side of the board, scrub, treat, and seal the top. While you are up there, do the same to the truss if it shows any water damage.

With a tenant being in the home, I kinda worry what they will see if you go full demo mode. Atleast look in attic/whatever (if no access, you can cut a 12x24 window flap in the sheetrock, that is easily repaired.

 

[Torvy]

Depending on the area, a dehumidifier may be in order as well.

Around here, low humidity is about 60% from April to October. Peak in July when 92% of the time the dew point is over 65 degrees.

The drying function of an A/C unit cannot keep up. Most people get a separate large unit to keep humidity down.

 

[ultrarunner]

Perma White by Zinsser has solved many a rental problem for me…

I have not kept up with formula changes but in the last 15-30 years ago it was common to have problems in baths and closets with exterior walls… the Zinsser product eliminated it as long as 2 coats used.

Zinsser® PERMA-WHITE® Mold & Mildew-Proof™* Interior Paint Product Page

PERMA-WHITE® Mold & Mildew-Proof™* Interior Paint is specifically designed to prevent mildew growth on the paint film in moisture prone areas in your home.

www.rustoleum.com

 

[paulsharvey]

We always had atleast somewhat OK results with dawn, bleach, and a toilet brush, and physically scrub the mold off. Then, let completely dry, and seal with a Kilz type product. Not 100% by any means, but the dawn allows the bleach to get to the spores. The scrubbing ensures that it's not just the surface getting killed.