AMSV Stone Accent Veneer

ACMV-Adhered Concrete Masonry Veneer- The Next Big Problem in Construction

It’s all the rage these days; fake stone siding (manufactured stone) as an accent on the front of a house.  You can give your home that mountain cabin look, right here in suburbia.  Manufactured Stone ACMV InstallSiding (or Adhered Concrete Masonry Veneer as it’s technically known) is a thin, man-made siding made to look like natural stones or rocks.  It’s basically molded concrete that looks like real rocks.  It’s normally installed over wood framing, but when installed incorrectly, it will let water in next to your wood framing, trap it, and wreak havoc on the structure of the house.  And so far, I’ve yet to see an install done correctly in Louisville. 

Story Time

A couple of years ago I was called in by a homeowner to look at his 2 year old custom built house.  His wife had tried to hang curtain rods on the front wall and his drywall was too wet and mushy to hold a plastic wall anchor.  They had no clue why things were so wet.  I was able to trace it down to the manufactured stone siding on the front of the house.  The builder had omitted all the important details with the install.  That day was began a fight with his builder that would last 2 years. For that entire period, his dining room was blocked off and unusable. The result: Attorneys were hired and things got ugly. The builder eventually repaired all of the water damage, stripped all the ACMV off, and replaced it with real stone (they did not try to install ACMV again). The final repair cost was close to $80,000.00.

Moisture intrusion experts have made the connection between manufactured stone veneer and traditional stucco (stucco homes in Louisville, KY are very rare to find).  When problems arise from a botched install, a house with manufactured stone veneer shows the same moisture related issues as a house with a botched stucco system.  It leaks behind the cladding and the water gets trapped. Then the house rots.  In fact, one of the brightest minds in the world of building science, Dr. Joseph Lstiburek refers to manufactured stone veneer as “lumpy stucco.”  He has a great article about that here: Stucco Woes.

Most manufacturers of ACMV are members of the Masonry Veneer Manufacturers Association or MVMA, who are now under the NCMA (National Concrete Masonry Association).  I know, enough with the acronyms already.  The MVMA puts out a installation guide (download the guide here) that is considered the “end-all-be-all” of how-to installation guides when it comes to manufactured stone siding.  When I am inspecting homes in Louisville KY, I refer to that guide and its details to show my buyers how things should be done.  The problem is I have never seen a home that has manufactured stone installed as the guide says it should be.  Most every detail is usually skipped, and we all know that when it comes to a home…

The Devil is in the Details

When big problems pop up with a house, you can usually trace its origins to a bunch of small things that add up to the train wreck at hand.  That seems to be the reoccurring theme with the ACMV installs I am seeing.  The most frustrating part for me as a home inspector is that by the time I get to see the house, most of the critical steps that must be done are covered up by multiple layers, and I’m left only to guess at what is (or isn’t) underneath the surface. But if the install crew can’t get the small, simple things correct, how could I expect them to actually do the really important stuff under it all.

Anyone who’s ever spent any time on a job site knows the attitude of most construction workers today.  In the many years I worked in the trades, one of the more popular things to hear was  “Looks good from my house,” or “We ain’t building a piano.” That’s a creative way of saying they don’t care.  They do not care if you have problems later on.  If it’s good enough to get things cleared, and them paid, let it roll.

Drainage-Drainage-Drainage

A wise man once told me that water and women can be lumped into the same category: They both always win. Never is that more true than when it comes to the ACMV installation on your home.  Water will find a way in. I repeat, water will find a way.  It will seep in around the cracks, and it will be absorbed into the chunks on concrete.  You didn’t think this stuff was waterproof did you?  It’s colored concrete. It absorbs the rain water, the sprinkler water, melting snow, etc.  What we must do as construction professionals is design and build a wall system that can control the water, and not let it reach the structural framing of the house.  The moisture will get past the concrete veneer; it’s what happens next that is vital to the integrity of your house.  Every type of siding (or cladding, if you will) needs to be able to drain the moisture that gets by it.

Take brick veneer for example.  Building codes have required a 1″ gap (brick manufacturers recommend a 2″ gap, by the way) between the sheathing on a house and the back side of the brick.  When the water gets absorbed by the brick (No, brick veneer is not waterproof either), that gap is there to make sure we don’t soak wood framing, and gives that moisture a path to escape at the base of the wall via weep holes.  Take a look at the detail below of a brick wall and you’ll see the drainage plane present.  The air gap is the glowing red area.  This allows the moisture a path to escape.

Brick Veneer Air Space

Here you can see the air space in a typical brick veneer wall (red space). The moisture is given a place to drain at the base of a wall. When done properly, this keeps things nice and dry.

 

ACMV (manufactured stone veneer) is typically installed on top of the wood sheathing on a house, and doesn’t have an air gap since it’s “stuck/mounted” to the framing, and not resting on the wall foundation in front of it (like brick veneer).  If you want a trouble-free install, you must create a drain path for moisture to drain and a place for it to escape at the base of the wall/window/door/etc.  If you do not have an escape point, the moisture will simply build up and rot out the base of the structure.  I’ve never seen a home with a weep screed (escape point) installed, and I look at new construction houses every week.  The builders around here are simply are not installing them.

ACMV-Wall-Detail

Here is the first image you come across in the MVMA install guide. I’ve highlighted the drain parts in red at the bottom of the wall.

There is a better way to build it

Hindsight is always 20/20, and now that the problems with manufactured stone are coming to the surface, we’re getting smarter about it from an engineering standpoint (but in the field it’s still screwed up).  If you actually read the whole MVMA install guide (you did read it, right?) you’ll see at the end of the document there are alternative methods to building the ACMV wall system.  These include a drainage mat or furring strips mounted to the sheathing of the wall.  In doing so you’ll essentially create an air gap between the house and the concrete veneer. Sound familiar?  Just like our age old friend, Mr. Brick Veneer, that air gap will allow for moisture control and drainage to occur, without the risk of the moisture soaking into the wood structure of the home.  Is anyone doing this you ask? Not here in Louisville, but I hope they start soon.  It’s likely going to take a couple of really big lawsuits to get this ball rolling.  The process does require more planning, work, and careful execution to pull off and and make work.  ACMV Furring Strip Detail

Here is a detail for the use of a drainage mat used in place of the furring strips.  This too, creates that air gap between the manufactured stone layer and the structure of the home.  ACMV Drainage Mat Wall

 

What to look for on your house

In future posts, I’ll break down the most commonly found incorrect areas, and give you details on how they should have been installed.  I’ll be sure to update this post as well, as I gather new info and images from the field.  If you have this material on your home and have questions feel free to contact me.  If you are in the Louisville, KY area, more than likely your home’s veneer was poorly installed.  I hate to say it, but I’ve never inspected a house that had a proper install of manufactured stone.  There are ways we can take minimally invasive moisture readings from the inside of the home to get a better idea of what type of damage may be occurring on your home.  If you’d like more info on this, just give me a call and we can talk about it.

PART 2: ACMV- TROUBLE AREAS AROUND WINDOWS & DOORS

In part two I talk about what should happen when you introduce doors and windows to your faux stone installation.

PART 3: ACMV- WALL DETAILS AND DRAINAGE

In part three I show you how the details around the walls should be handled, and how to make sure the water doesn’t build up behind the stone veneer.

The ACMV diagrams from this series were all taken from the MVMA guide. I will sometimes remove extra details or color certain sections to make them a bit easier to understand. If you want to look at the originals, download the full MVMA manual.

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Ben Hendricks

owner at ABI Home Services
Hi, I'm Ben, and I inspect houses.I grew up with a hammer in my hand, and have been a professional home inspector for 10 years.My blog is here for info about Home Inspections around the Louisville KY area, and just about anything construction related.
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Comments

comments

7 replies
  1. Ken Jones
    Ken Jones says:

    After reading this I think I’m screwed. Can you come up to Michigan and look at my house? I’m afraid I have rotten walls too.

    Reply
    • Ben Hendricks
      Ben Hendricks says:

      Hi Ken, MI is a bit too far for a inspection for me (I’m in Louisville, KY). I do encourage you to find someone local who knows what they are doing and have your place checked out. If you strike out completely let me know and I’ll see about making a special trip for you.

      Reply
    • Ben Hendricks
      Ben Hendricks says:

      I’ve not seen Genstone used around here Mark, so I can’t give you a certain answer. I will tell you that any product that puts lots of holes in your walls, and lets water get behind it will be a problem over time. I’m a big fan of drainage mats (also known as a rainscreen) like this one: https://www.mtidry.com/products/rainscreen-drainage-planes If a rainscreen is used properly, it should take care of the problem.

      Reply
    • Ben Hendricks
      Ben Hendricks says:

      Not that I’ve seen Scott. Not yet anyway. Keep in mind the product performs well if installed correctly (with the proper drainage). The issue that I’m seeing is builders and contractors are not following instructions. As we all know, the devil is in the details.

      Reply

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