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Masonry Best Practice – Rock / Limestone with a Rainscreen

I really like Masonry clad buildings.  It’s tough to beat the longevity, durablity, and easy maintence of a rock or brick facade.

Hugh Jefferson Randolph house I built a few years ago with a beautiful brick.

From a Building Science perspective Brick is a terrific building material because it’s got a built-in air cavity between the brick and the house.  It’s traditional for Mason’s to leave 1″ of air space between the back of the brick and the framed wall.  Brick & mortar are naturally porous and WILL LET WATER pass through so this 1″ air gap is vital to drain the moisture out of the cavity.

Photo courtesy of medcot.com.  Brick with Tyvek CommercialWrap & a Mortar Net at the base

This airspace is hugely important.  It allows the brick to absorb water then dry to the front or the back of the brick.  Remember that brick is considered a “Reservoir Cladding” which means that it can soak up literally 10’s of gallons of water then slowly release this moisture over time.  The waterproofing behind the brick is of immeanse importance in our Hot/Humid Texas climate.  Here’s why:  Our hot climate means we run the sprinkler system ALOT and our brick exterior walls might be getting soaked 2-4x per week year round at 4AM when a homeowners landscape gets watered.  Then when the sun hits that same masonry wall at 10Am the vapor drive effect happens and can destroy a house over the years with the wetting of the walls.  See this video I shot to get an idea of the problem.

 The main point of the video is that we need a low perm, and very high quality housewrap that’s 100% liquid water in-permeable.  I use Tyvek Commercial Wrap exclusively for my brick/rock houses.
  Ok, so Brick is relatively straightforward with it’s 1″ air gap but not all Masonry has that air space.  In fact, many rock exteriors here in Texas have zero gap behind the stone as they are fully mortared to the house.  Here’s where a rainscreen product becomes necessary to force the air gap.  The photo’s below are of a house utilizing Keene Driwall Rainscreen for a Limestone Rock install that wasn’t going to have an airgap otherwise.  The product on the walls is Driwall 10mm.

Keene Driwall laid directly over the fully detailed Tyvek weather barrier.

This builder used Drainwrap, but I’d use CommercialWrap without the crinkles and a lower perm rating.

Here’s a good shot to show why it’s necessary.  Random pattern rock is prone to total fill mortar.  This poduct creates a rainscreen

The air gap this creates is vital to ensuring moisture is kept out of this wood framed house. 
Here’s a sample of the Keene 020-1 product.  This side goes against the Tyvek and provides a stand off. 

This side has a filter fabric that lets water through but won’t allow mortar to clog the air gap. 

I would consider this a Best Practice install of a Masonry Rock exterior.  This would also work for Stucco, Thin Stone/Brick, Manufactured Stone, and even could be used to create a rainscreen behind siding.
-Matt Risinger
Risinger Homes in Austin TX
Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.
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