Vapor Barriers


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Old 01-29-11, 03:48 AM
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Vapor Barriers

Ok, I'm a little confused about what exactly qualifies as a vapor barrier. I know that certain paints are good for this, but what specific materials are used for a vapor barrier?
 
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Old 01-29-11, 04:39 AM
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Welcome to the forums! As far as I know, no paint will suffice as a vapor barrier. Vapor or moisture gets behind paint and it's toast. Now, in a shower situation, you can use a product like Redgard on your concrete backer underlayment to help, but a good solid vapor barrier of 6 mil plastic is always a better solution.
Fill us in on your ultimate goal. What is your project? Which room? How big? What will your final wall covering be?
 
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Old 01-29-11, 04:51 AM
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Originally Posted by chandler
Welcome to the forums! As far as I know, no paint will suffice as a vapor barrier. Vapor or moisture gets behind paint and it's toast. Now, in a shower situation, you can use a product like Redgard on your concrete backer underlayment to help, but a good solid vapor barrier of 6 mil plastic is always a better solution.
Fill us in on your ultimate goal. What is your project? Which room? How big? What will your final wall covering be?
Thanks for the reply. Actually my "project" is a big old 1889 Farmhouse that I recently bought. Attic is only partly insulated with fiberglass bats. . Interior walls have cracks and peeling paint and wallpaper. I was told by a friend that certain wall paints act as an effective vapor barrier. I am planning on repairing the plaster walls, removing all wallpaper and painting. I recently was reading about vapor barriers and how old houses need to "breathe." This is why I asked what materials are used as vapor barriers and what should I look for in an old house.
 
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Old 01-29-11, 05:37 AM
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I'm going to let our paint guy chime in on any knowledge he has on paints. He'll be along shortly. As far as breathing, all houses need to breathe. I doubt your house has a breathable barrier on the outside, such as Tyvek or Typar, due to its age. Vapor barriers are generally installed between the framework and the final wall covering to keep moisture behind the wall and breathing to the atmosphere.
Generally what shape is the plaster in? Is it worth repairing and saving? Would you be better served in the long run by gutting the plaster and starting again with drywall? That way you could insulate the walls properly as you go. Just some thoughts until we hear from marksr.
 
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Old 01-29-11, 05:42 AM
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While not as effective as a plastic vapor barrier, solvent base paints/primers can be somewhat of a substitute for a vapor barrier.

From your description of the work being done on the interior, an oil base primer would be in order anyway. You should be aware that the peeling paint might contain lead!

On the exterior while an oil base primer does the best for priming the wood, we've found that on the older houses that don't have a vapor barrier it's best to use a latex primer as it will let the house breathe some. Too good of a paint job on the exterior of these old houses often results in premature paint failure


Just read Larry's post, he makes a good point about gutting the plaster! Not only does that allow you to update the insulation, you can also inspect, replace, move or add on any electrical. A lot more work but probably worth the effort.
 
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Old 01-29-11, 05:45 AM
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Originally Posted by chandler
I'm going to let our paint guy chime in on any knowledge he has on paints. He'll be along shortly. As far as breathing, all houses need to breathe. I doubt your house has a breathable barrier on the outside, such as Tyvek or Typar, due to its age. Vapor barriers are generally installed between the framework and the final wall covering to keep moisture behind the wall and breathing to the atmosphere.
Generally what shape is the plaster in? Is it worth repairing and saving? Would you be better served in the long run by gutting the plaster and starting again with drywall? That way you could insulate the walls properly as you go. Just some thoughts until we hear from marksr.
Because I am restoring and not "renovating" this house, gutting to the bare bones and putting up Sheetrock on all walls is not an option. The cracks in the plaster are normal for the age of the home. All attempt at restoration will be made.

Yes, fully aware of lead paint possibility and precautions are in order concerning its removal.
 
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Old 01-29-11, 05:58 AM
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Then, undercut the cracks and fill with a product like Rock Hard Putty by Durham's, sand and prime and paint as Marksr said. He gives good advice on breathability as well.
 
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Old 01-29-11, 06:02 AM
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Originally Posted by chandler
Then, undercut the cracks and fill with a product like Rock Hard Putty by Durham's, sand and prime and paint as Marksr said. He gives good advice on breathability as well.
That was my plan all along. Just wanted to know what are the specific materials used as a vapor barrier.
 
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Old 01-29-11, 06:05 AM
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I've always used a setting compound like durabond to repair plaster. Both durabond or rock hard are a bear to sand so it's best to do a neat job and then dress it up with regular joint compound - it's easy to sand
 
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Old 01-29-11, 06:17 AM
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Originally Posted by marksr
I've always used a setting compound like durabond to repair plaster. Both durabond or rock hard are a bear to sand so it's best to do a neat job and then dress it up with regular joint compound - it's easy to sand
Thanks for the tip, however I was asking about specific vapor barrier materials. I know how to repair plaster.
 
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Old 01-29-11, 03:51 PM
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Energy Savers: Vapor Barriers or Vapor Diffusion Retarders

This site discusses "Vapor Barriers" and does mention that most paint coating will impede mosture flow.
 
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Old 01-29-11, 03:58 PM
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Yep, aware of that. But what I'm really wanting to know is what specific materials are used as vapor barriers. I have heard of plastic being used between the insulation in the attic, but what kind of plastic?

Also, where else do you need a vapor barrier? Basement?
 
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Old 01-29-11, 04:17 PM
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6 mil plastic. You need the vapor barrier between your studs/joists and the final wall covering toward the living or warm space.
 
 

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