Reuben's Home Inspection Blog


Invasive Moisture Testing: No, I'm not kidding.

I recently had a featured post here on AR about invasive testing vs infrared scanning on stucco homes, where I concluded that invasive moisture testing is the only reliable test method for stucco homes in Minnesota.  Russel Ray, a San Diego home inspector, wrote an opposing post which was also featured.  His post was titled Invasive "testing"?  Are you kidding?.  In his thought-provoking post, Russel Ray opines that invasive moisture testing is outdated.

Today I'm going to explain why invasive moisture testing is not outdated, as it's the only reliable option in Minnesota, and I'm also going to discuss the differences between interior and exterior moisture testing.  But not in that order.

To gather information about this blog, I spoke with moisture testing experts from four of the larger stucco testing firms in the Twin Cities: Barry Eliason of Private Eye Home Inspections & Moisture Testing, Wayne Shellabarger of Acuity Engineers, Inc., Alan Powell of Certified Moisture Testing, and one other expert who wished to remain anonymous.  I asked them about their preferred testing methods, and asked them to explain why.  All four can provide both interior and exterior testing.

Interior vs. Exterior - The Basics

Exterior testing of stucco is done by drilling holes in the stucco at suspect locations, sticking a moisture probe in to the wall, and measuring the moisture content of the wood or wall sheathing with a special moisture testing device, such as a Delmhorst Moisture Meter.  Interior testing is done by drilling holes in the interior walls, and then sticking a long moisture probe through the wall to the exterior wall sheathing to take a moisture reading.  These are both reliable testing methods.

Interior vs. Exterior - Cosmetic Issues

Whether holes are drilled in walls from the exterior or interior, the walls won't look exactly the same when the work is done.  I've inspected many stucco homes that have had invasive moisture testing done, and in every case the holes were quite inconspicuous.  The person drilling holes in stucco will come equipped with a wide range of sealants to fill the holes when they're done, and the resulting 1/4" holes are barely noticeable once filled with with matching caulk.  For interior testing, the holes aren't as easy to hide or patch.  If holes are drilled in drywall, they'll obviously need to be patched and painted over again.

Cosmetically, exterior testing is certainly preferred, as you really need to walk around the exterior of the house and carefully look for the test locations; they're not obvious.

Interior vs. Exterior - Holes In The Stucco

One concern with drilling holes in stucco is that this will compromise the drainage plane behind the wall, and the caulking used to fill the holes won't get far enough in to the wall to seal the drainage plane again.

Wayne Shellabarger, who is opposed to exterior testing, said that he has found holes in the drainage planes that were never properly sealed up after invasive testing was performed.  I asked him if there was water damage caused by the breaks in these drainage planes; the answer was no, but he was also quick to mention that in the cases he has seen, the holes were only a year or two old.

Alan Powell said that while the holes they drill in stucco are 1/4" holes, they don't drill through the drainage plane behind the stucco.  The only thing that penetrates the drainage plane behind the stucco are the pin probes on the moisture testing device, which leaves 1/8" holes.  When you think about all of the holes that get created in the drainage plane with staples and whatever else, the holes made by the pin probes will be quite insignificant.

After over a decade of invasive testing and having tested thousands of homes, none of the companies that perform exterior testing have had a single reported problem with this testing method.

Interior vs. Exterior - Accessibility

The biggest problem that Barry Eliason expressed about interior testing is that there are oftentimes interior wall surfaces that make testing impossible in some locations.  There are several places where holes can't be drilled, such as through bath tubs, shower walls, tiled walls, and cabinets just to name a few.  Alan Powell also expressed concerns about being able to test in the proper places on interior walls; windows usually leak in the corners, and to properly test the right areas, the wall sheathing directly behind the walls studs is the most critical area to test.  This area can't be accessed from the interior walls.

On the other hand, Wayne Shellabarger said that if a home has moisture problems, there will still be enough accessible areas for him to find problems, even if he can't find every one.

Infrared, revisited

Some home inspectors say they've had good luck using infrared cameras to find moisture behind stucco walls, but I say they don't know what they're missing.  I think everyone can agree that invasive moisture testing is accurate; if a tester drills holes and sticks moisture probes in the wall, they'll be able to locate moisture if it's there.  To know if an infrared camera can reliably detect moisture in walls, one would need to scan a house with an infrared camera and then compare those results to an invasive moisture test.  If an infrared camera could reliably find wet areas behind stucco, it would be useful.

I have yet to hear from a single home inspector, anywhere in the country, who has performed infrared scans on houses, compared those results to an invasive moisture test performed at the same time, and can still claim that infrared scans on stucco houses are reliable.

All four testing companies that I interviewed said the same thing about infrared inspections on stucco homes: they're unreliable.  Each company shared the exact same experience with me.  They were excited when infrared cameras came on to the market, they purchased infrared cameras, they went through extensive training on the use of IR cameras, and then they began using IR cameras on houses before performing invasive testing.  They all say that IR cameras are a completely unreliable way of finding moisture behind stucco.  Wayne Shellabarger's web site says they use infrared cameras as a starting point before performing invasive testing, but he told me they no longer even offer that service because it has proven to be a waste of time.

Non-Invasive Moisture Meters (aka - surface scanners)

Russell Ray mentioned in his blog that he has had a 100% success rate testing for moisture on stucco homes in California using a surface scanner, such as a Tramex Moisture Encounter Plus.  This device is a fairly inexpensive non-invasive moisture detection device that, according to the manufacturer, can be used on "drywall, wood, plaster, brick, ceramic, porcelain tiles, resilient flooring, laminates, asphalt composition shingles and most building materials."  Stucco isn't listed.

I called the manufacturer to ask about using this device on stucco (I spoke with Penny).  She said that if the stucco has metal lath, it won't work.  This is the same with all non-invasive surface scanners.  If the scanner is used from the interior, it also won't work, because it won't read nearly deep enough in to the wall to reach the exterior wall sheathing, which is the part that needs to be tested.

When Russell or anyone else has a 100% success rate using a surface scanner on stucco, that means they're not using it on the same type of stucco that we have Minnesota.   Stucco homes in Minnesota have metal lath.  Surface scanners will have a 0% success rate on this material.  To echo Russell's point, regional differences are huge.


Here in Minnesota, performing an invasive test on stucco is the only way to know what's happening behind the stucco on a newer stucco home.  Problems can't be positively identified using visual inspections, surface scanners, or infrared cameras.  Visual inspections will often provide clues that a problem exists, and so will infrared scans, but that's all they can do.  Many times, stucco homes will have serious problems without any visual or infrared evidence.

As for the interior vs. exterior testing debate, they both have their pros and cons.  If you're buying a newer stucco home in Minnesota, have an invasive moisture test performed.  You'll need to hire a company that specializes in this, such as one of the companies that I listed at the beginning of this blog.

Oh, and of course, you'll need to get special permission from the seller to do this.  Drilling holes in walls is invasive; home inspections aren't.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 10 commentsReuben Saltzman • March 01 2011 06:18AM



Great, great, great blog about a very significant issue here in Woodbury, MN. In fact, I have printed this out and am keeping it in a file until such time I require it. Thanks!

Posted by John Durham, MS, MS, ASP, ARS (Durham Executive Group - RE/MAX/Results) about 8 years ago

Once a stucco inspector was at the house at the same time as my inspection.  When he was done, the holes were very small and he used various caulks that had colors to almost exactly match what he was doing.  You had to really look hard to see the holes.

I use the Tramex also, but not for synthetic stucco applications.  It only sees 1/2", and EIFS is much thicker than that.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) about 8 years ago

Reuben, a very good article. I do have to wonder about "visual non invasive testing" if you going to be drilling holes and using sensing devices. 

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) about 8 years ago

Hi Reuben, very informative post.  Once again you have done your homework.  Thanks

Posted by Dale Ganfield about 8 years ago

John - thanks, I appreciate it.  Hopefully this will mean more to buyers considering the fact that I don't offer invasive testing.

Jay - I've had the same experience.  Once the stucco holes are patched, they're nearly invisible.

Robert - thanks.  What do you mean about "visual non invasive testing" ?  I'm a little confused.

Dale - thank you sir.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago


Great post, I have another Stucco home this week and I do not perform a full stucco inspection. The issue around here there is no certified Stucco inspectors.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) about 8 years ago

To answer you Reuben, “visual non invasive testing” is a term used to describe our inspections. It can be found in various forms or versions in our contract wording or standards of practice. As you use more and more testing and sensing equipment, the less visual your inspections become. In the comment I was not referring to your discussion of 'invasive verses non-invasive methods' but rather the use of indirect means verses visual only.


Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) about 8 years ago

Donald - it would be nice if you had people in your area that offered this service, wouldn't it?

Robert - thanks for the clarification.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago


Infrared is a tool just like any other and it has limitations just like any other tool.

As far as using a moisture meter on the surface of stucco, it does not matter where you are, all stucco has a metal lath that will give false positives. No if he is testing EIFS then a moisture meter will work provided the moisture is still present and the foam under the stucco is not too thick for the meter to read the sheathing.

I have seen one home where they did exterior moisture tests not with 1/4 inch holes but they actually cut out a 8" x 8" section of the stucco (after the tramex said it was wet) and there was no damage in these areas untill a year later when I went back out to the property.

The mositure barrier behind the stucco was not repaired properly and we had moisture damage to the sheathing. The company that did the testing to prove the contractor screwed up is no a defendant.


Thanks for sharing, you have some great posts here, I may re-blog your dirt on filters post.

Posted by Scott Warga (ACSI American Construction Specialists & Investigations) about 8 years ago

Scott - do you have people in your area that specialize in invasive stucco testing? 

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) about 8 years ago