# Thin Brick Underlayment



## Cache (Sep 18, 2007)

Anyone have any suggestion for the underlayment behind an exterior thin brick application? Local code says the minimum required is 2-layers 60 minute paper.

Masons around here usually use a layer of 15# felt, but many people are starting to insist on Tyvec housewrap. It is my understanding that Tyvec wrap is only a vapor barrier and will not serve as a water proofing layer like felt. Obviously, thin brick is water permeable so the waterproofing layer is necessary. Some have suggested doing a layer of Tyvec along with a layer of felt. Seems to me that such an application would sort of defeat the purpose of the Tyvec.

What say the gurus here on CT?


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## artisanstone (Nov 27, 2007)

It boils down to whatever the brick supplier recommends. That said, I lean towards Tyvek + tarpaper. As you put your first coats of mud on, the tarpaper absorbs water and swells. When it dries, it leaves a very small void for water drainage behind the paper. This deals with actual water infiltration (rain). Vapor migration from the interior can sometimes be a different story.


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## Cache (Sep 18, 2007)

artisanstone said:


> It boils down to whatever the brick supplier recommends. That said, I lean towards Tyvek + tarpaper. As you put your first coats of mud on, the tarpaper absorbs water and swells. When it dries, it leaves a very small void for water drainage behind the paper. This deals with actual water infiltration (rain). Vapor migration from the interior can sometimes be a different story.


It turns out that Dupont's Tyvek specs require both Tyvek and then felt. They won't warranty the tyvek if the mortar is in contact with it. So they specify tyvek on sheething, followed by "building paper", then lath/scratch coat etc... for stucco, brick, and rock veneer applications.


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## 6stringmason (May 20, 2005)

I always go Tyvek then felt paper.


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## eekie34 (Jun 14, 2008)

then whats the deal with the tyvek stucco wrap?


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## Cache (Sep 18, 2007)

eekie34 said:


> then whats the deal with the tyvek stucco wrap?


I think you're right. The Tyvek Stuccowrap is allowed to be placed directly in contact with the lath/scratchcoat, but only in locations where the local building codes accepts it as a substitute for two layers of building paper.


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