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c gary
Dark haze in drywall at rafters
c gary

I'm hoping someone can point me in the right direction. I'm not sure who to consult. I live in upstate SC in a 2 story house with a cathedral ceiling and an open loft area. The actual ceiling is dropped down from the roofline to allow ventilation. I've had a propane decorative 30000 btu heater for about 10 years as supplement to a heat pump that's 3 years old. The house itself is 30 years old. 3 years ago I sc****d the popcorn off the ceiling, had all the drywall joints re-taped and had the ceilings professionally primed and painted a light blue. Last winter my wife started noticing that there were dark lines at every ceiling joist. Very uniform the full length of each joist/ rafter. I've been told it is because of the different temperature of the joists and they attract dust, soot, etc. My question is why now? For 27 years it didn't do it. Same LP heater, same roof, same duct work. How do I pinpoint what changed. Alo, should I have posted in another section?
Thanks in advance,
Gary

A. Spruce
Re: Dark haze in drywall at rafters
A. Spruce

What you describe sounds like "ghosting", basically, the drywall is cooler where it is attached to framing, thus it collects condensation as outside temps dip and inside humidity rises. The result is that condensation forms on the cooler areas of the walls and ceiling, along the framing members, this moisture also attracts ambient dust in the air, forming the shadows you are now seeing.

What are the cures, depends on how bad the problem is. If you've got a lot of humidity, you may want to look into a dehumidifying system for your home. If your relative humidity isn't that bad, then adding more insulation across the tops of the ceiling joists will help curb the condensation. As for what to do with the existing ghost lines, simply repaint with a good quality paint.

ordjen
Re: Dark haze in drywall at rafters
ordjen

Spruce is correct. The reverse situation can sometimes be seen on house exteriors on cool mornings where the dew does not form on the areas where the studs are. The studs transmit the house's interior warmth to the exterior better than the insulated wall cavities. Dew does not form on the warmer stud areas.

As a painting contractor, I would often see such shadowing in homes on ceilings and outside walls. As Spruce says, these are cooler areas upon which slight condensation forms, usually not enough to be seen as being wet , but enough to catch airborne dirt. Often the cause of the shadowing is poorly insulated spots, either through poor installation, or possibly strong air currents having blown blown in insulation away from areas close to eave vents.

In some cases, I have been able to see where individual drywall screws were located, because the metal screws or nails conduct cold to the interior and more condensation forms on their heads.

c gary
Re: Dark haze in drywall at rafters
c gary

Thanks for the replies....makes sense except....why did it just start after 30 years in the house? Nothing changed except new paint. Could the vent free LP heater be emitting more soot than before? Could my ducts need cleaning? We don't smoke or burn candles. What could have caused it to start?

A. Spruce
Re: Dark haze in drywall at rafters
A. Spruce
c gary wrote:

Thanks for the replies....makes sense except....why did it just start after 30 years in the house? Nothing changed except new paint. Could the vent free LP heater be emitting more soot than before? Could my ducts need cleaning? We don't smoke or burn candles. What could have caused it to start?

It is hard to say, could be the old paint color and patina was more conducive to hiding the ghosting. Could be that the heater is increasing the humidity of the house. Could be that the new paint is of a lesser quality or applied poorly.

To rule out the heater, you might want to have it serviced to make sure that it is still operating properly and at peak efficiency.

Mastercarpentry
Re: Dark haze in drywall at rafters
Mastercarpentry

Howdy Neighbor! GSP area here and have been here much of my life.

It's ghosting and the culprit is humidity which is permeating the paint. It was doing the same thing with the previous color but that paint didn't shift tints as much when damp. I'll even bet the old paint was white which shows far less tint shift when damp. Only coastal humidity is worse than ours here.

Not familiar with that heater but un-vented gas appliances (LP or natural) introduce a lot of humidity when used. That can be gas logs, a stove, or a wall-mount heater. I've seen well-sealed houses here visibly wet inside from this adding to our high atmospheric humidity.

The easiest solution is to go back with the paint which worked well before (hope you can stand that color) or to reduce the indoor humidity. If you don't want the old color then you've got some experimenting to do. Go to a real paint dealer, not a 'dumb box' store, and have them dab a sample of your chosen color (or as close as they have to it in standard stock) onto a piece of primed drywall, hit that with the blow drier, let it cool, then put a few drops of water on half of the spot smeared around with a finger. In about a minute you'll either see color shift where wet meets dry or you won't. You may have to try several different paint types and brands before you find one which does OK. Reds and greens seem to be the worst offenders with blues following. Whites rarely show much tint shift when wet.

When all else fails, try the test with an exterior paint- it's made to resist the wetness without tint shift where interior paint isn't made to handle wetness. And for comfort sake too think about getting the humidity down or at least to keep a constant airflow going. We almost hit 90 the other day so summer's here again for 5 more months and our humidity will come with it. Handling that may fix the ghosting if you want to try that approach first. Your call. Make sure your crawlspace vents are open, lots of humidity trouble from that around here even in the winter.

Phil

ordjen
Re: Dark haze in drywall at rafters
ordjen

What Phil is describing as "tint shift", has a technical name: surfactant leaching. It is where water soluble tints migrate to the surface under high humidity conditions. Here in Northern climes, it is often seen on bathroom walls, usually on the cold outside walls as a result of high humidity from showers. Phil is correct, certain tints are more prone to this migration than others. White does not migrate because it is not a tint at all, but, in quality paints, it is the metallic titanium dioxide which makes the paint white.

To minimize this phenomenon, buy only quality paints that use only pure titanium dioxide, rather than cheap fillers such as calcium carbonate (chalk) and silicas (sand). Choose a paint that is 100% acrylic resin as its base, rather than cheaper acetates or vinyls (PVA or Vinyl Acrylic).

Higher sheen paints are less prone to this condition. Why? in higher sheen paints, such as semi-gloss, the white titanium dioxide pigment is ground extremely fine and pack together to form a very dense, more moisture resistant coating. Moisture just does not enter the paint in the same fashion as in lower seen paints. This is why higher sheen paints wash much better than flat paints. Because moisture does not enter the paint film, the tint pigments don't tend to migrate.

In Behr's higher line Ultra paints, an additional step is taken: Behr introduces an additional metallic particle which is only several nanos is size. A "nano" is a particle one billionth of an meter in size, i.e. 1000 million of these little fellows can line up in a distance of about 39 inches! This is not grinding the material smaller, this is chemistry. These nano particles fill in the microscopic gaps which exist in the conventional paint film. It makes for an extremely dense paint film. It increases the moisture resistance of the paint and makes it inherently mildew resistant. Again, since less moisture penetrates the surface, it is less prone to the surfactant leaching.

Traditionally, higher sheen paints were required in baths with showers due to the high humidity. The Behr Ultra allows even a low sheen eggshell finish to be used in that bath. I personally use Ultra Matte (flat) throughout my house, including the baths, and have seen no evidence of surfactant leaching.

Sorry if this is sounding like a blatant commercial, but I really do believe in this product. It is also reasonably priced, in the low $30 range.

A. Spruce
Re: Dark haze in drywall at rafters
A. Spruce

Ordjen, you're such a Smar-T-Pants! I could almost forgive you your affinity for Behr products. :p :cool:

As always, my good man, excellent info!:cool:

I'd like to insert here that I personally know the heir to the Behr throne. He's a very nice person, someone you'd all like very much. Doesn't change my opinion on Behr products, however, knowing that the "head dude" is a great person actually means a quite a lot.

ordjen
Re: Dark haze in drywall at rafters
ordjen

Spruce,

Thanks for the compliments. I do try to give my customers my best opinion. I will steer them away from certain products, even if it says Behr on the label. No manufacturer makes equally great products all across the line of products they sell. All the majors sell "good , better and best". Unfortunately, it is sometimes bad, not so bad, and acceptable :(

I always caution people who are hiring a painter not to accept merely that he is using Sherwin Williams, Ben Moore, etc., but to ask specifically what label of that brand he intends to use. They should then call the paint store and ask exactly how good that paint is relative to all the lines. A painter that is not using top of the line paint is not looking out for your best interests. It is his labor that is expensive. He should not be chintzing a few dollars on a gallon of paint to pad his profits. I will concede that there are times when "good enough" is warranted.

I have used Behr's Ultra and Marquee paints on my own home, both interior and exterior, and think they are as good as anything on the market presently. especially when price is factored in, I don't think they can be beat.

A. Spruce
Re: Dark haze in drywall at rafters
A. Spruce

You're welcome, and your not alone in trying to provide clients with the best possible information for their needs, this is something that I believe most of us strive for. A well informed client is a happy client.

While I'm not a painter by trade, I certainly have done my fair share of it over the course of my career. When it matters, Kelly Moore is my brand of choice, and because I use the same supplier, they know me well and steer me toward the products best suited, even if it's not their own. I also like that they've got the color codes for all of their competitor brands, so you can get good matches on colors.

ordjen
Re: Dark haze in drywall at rafters
ordjen

Spruce,

The "big box" stores will always have a disadvantage to the local paint store. During my contracting days, I had a "handshake" relationship with my main paint supplier, which was a "mom and pop" type store. I could call in an order and have it ready by the time I drove over to get it. Just had to sign a receipt and leave. If they were really busy and I needed something in the store, i would just hold it up and say " I am taking this", to which they would reply, "gotcha". Try that at the big box store!

The smaller paint stores tend to have longer duration, more knowledeable help, often with some background in the painting business. I will admit that I am somewhat of an anomaly for a big box store, but knowledgeable people are occasionally to be found.

My experience with the large company owned chains, such as Sherwin Williams, is that they aren't any better than the big box stores.

I sometimes feel like a voice out crying in the wilderness when talking to my managers about service. Certainly price is of concern , but as far as I was concerned, SERVICE was the determining factor of where I did business. A contractor is selling his knowledge and skill in units of time. Time wasted standing in line at a big box store costs him dearly. My business was mainly upper end residential painting. A minor variance in the cost of the actual paint was almost immaterial.

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