Dark Marks On Walls

Danno6102

This is in a stairwell. The walls were precast concrete panels. The stairwell was considerably cold, so they decided to fir out the panels with metal studs & put board insulation between them & attached drywall to the metal studs. First winter they got these dark lines. It wipes off on your fingers if you rub it. I'm thinking condensation coming through the metal suds & drywall & attracting dust.

Anybody have any ideas what can be done to cover this up & prevent it from reoccurring.

Thanks,
Dan

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neolitic

It's called thermal bridging.
One can try an oil base stain blocking
primer, but I'm not sure if it will
be a permanent solution.
Try Google.

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Frankawitz

we just wash it down with TSP in spray bottles you can get at Home Depot, spray it wipe it down then prime Benjamin Moore's Freshstart Primer then paint two finish coats of paint. Good luck


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concretemasonry

The real problem is the thermal bridging or "short circuiting" caused by metal studs. They kill or cut many insulation in half and all the heat loss is where ther occur.

That is the cause and you can try all the surface applications, but if the is any moisutre in the air, it will be attracted to the surface where the stud is. The slightly high moisture content on the surface, the more dust what will be attacted. The moisture and dust are in the interior no matter what the coating is. Whatever you put on the surface, is just a band-aid and not a real solution.

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Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

hoya

If the residue feels kinda soapy or sticky it could be the surfactants (soap Stuff) in the paint itself. Can be cause by temp. change and moisture. Rub a little water on it and if it suds or bubbles up ---thats it.

Cure wash down the walls with soft sponge and a mild detergent.

painterman

Sure looks like Thermal Bridging .Check out this site http://www.inspect-ny.com/interiors/ThermalTracking.htm

WisePainter

I hate to tell you this but every time you finish cleaning the offending lines off, someone arrives about 45 minutes after and draws the lines back onto the wall.
Next time clean the lines as you normally would and then hide...when said person arrives confront them and tell them how much it upsets others when they reapply the lines to the drywall.
Hopefully they will see reason and stop doing it.

Please no PM's, I have had a long day.

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hoya

I like that website

capital city

I have also seen this with fireplaces that are not vented properly. Not sure what happens but have seen it a handful of times. Once the homeowner fixed the ventilation problem and primed and painted it didnt come back

Danno6102

So, Thermal Bridging is what it's called, seems like I was correct with my diagnosis. I figured there was no solution to the problem, only bandaides.

What about tearing off the drywall, installing 1/2" foam board or fanfold & then putting up some new drywall? This would at least give it a thermal break except for the screws.

P.S. Just to clarify, I didn't do the work. Was just asked to look at it.

painterman

Is this the only area in the house that this is happening? If so foam should stop it but it will show up on the screw heads. If it is in more areas of the house don't rule out an exhaust leak from a gas heating source. The gas company can us a sniffer to source the leak. Good luck

concretemasonry

The foam does not stop the thermal bridging unless it totally separates the drywall from the wrinkled tin studs.

The studs transfer the heat because of the very high conductivity of the steel. The drywall is usually in contact with the stud faces, so the shortcircuiting is transfered to the dry wall. Since the dry wall has slightly less conductivity, it does not spread to the sides very far, so the cold spots on the wall will be a little wider than the stud face width.

It is a classic situation and you can even see it with wood studs. As an example how bad the steel studs are, A 6" steel stud wall (at 12" o.c.) reduces the effective valuse of the R19 insulation to give you a R11 or so for the wall.

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Dick

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Bender

Good post. I've only seen that once or twice over the years but never knew the technical name for it. Thanks

Workaholic

About time you decided to make your first post lol.

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Chris Johnson

If you can, use a thermal imaging camera (you may be able to borrow one from the local utility company) and snap a picture, now show the client and let them know what Concretemasonry said.

Heat the area and good chance it disappears.

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Chris

Tom Struble

that mold website is coolso is it mold or dirt that gets attracted to the condensation on the drywall caused by thermal bridging?

Frankawitz

I like the website, very infromative, Thanks for the link. I would think that if the tranfer of heat is lost that much, That the steel stud manufactures would apply a foam strip like sill seal on the edges to stop the steel stud from transfering the cold along like conductive heating. this would stop the Ghost lines, Like with the spray foam it seals everything.


www.frankawitz.net

Bender

Well, you know how shy I am

Dmax Consulting

I've never heard of thermal bridging until this. I learned something new today.

Happy new year!

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ModernStyle

It could be a sign of paranormal activity.
Use the lines as a guide and paint stripes down it,then it will not be noticed.

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