What is the definition of wet and what constitutes a "wet" building material?

Here we describe and give examples of the level of moisture that would be considered critical or harmful in various building materials and we describe the problem of giving any single quantitative definition to "wet" or "damp".

Definition of "Wet" - when is a substance considered "wet" ?

Question: arguing with my building manager on the meaning of wet

2019/02/12 Anonymous asked

Just arguing with my building manager of 200+ units on the meaning of wet.

Personally removed a glistening piece of wood lathing that could almost be wrung out like a sponge. - anon by private email

Reply:

In the most general terms the definition of the word "wet" is too often given in self-referential terms such as

• adjective: covered or saturated with water or another liquid
• noun: liquid that makes something damp
• verb: cover to touch with liquid, moisten

In building science a more-useful and defensible definition of what constitutes "wet" depends on whether or not the moisture level in a substance is

• detectable
• likely to be problematic

Just how those two questions of wetness in building materials may be answered depend on

• the problem being analyzed
• the materials involved
• possibly the temperature of the material, an actual measurement of moisture content, and surrounding air moisture and temperature and dew point
• objective observations or measurements of humidity, relative humidity, moisture, actual wetness, or moisture content.
• science supporting a specific moisture level or moisture content in material that is known to cause trouble: rot, mold, insect attack, bacterial growth, etc.

I agree with you that if you can touch a building material like wood lath comprising part of an indoor wall or ceiling and your finger comes away visibly covered with water (assuming as is almost certainly the case that it is water and not some other liquid) then that material is "wet" both subjectively and reasonably objectively.

However there are plenty of other "wet" thresholds that if crossed can mean trouble even though touching the material may not leave visible water on your finger.

Beyond palpating bodies of water (stick your finger in the ocean), any single "right" answer to "what is wet" across all materials and circumstances would be indefensible.

Examples of Different Criteria of "Wetness" or Moisture Level in Building Materials

• Critical moisture level in drywall:
  
  In assessing the risk of mold growth in drywall, a moisture level similar to the danger level in wood is probably a reasonable threshold - 18% moisture content;
  
  I find that different mold genera/species grow on drywall at different heights above the floor as the moisture gradient in the drywall varies - S. chartarum likes the wettest paper, Aspergillus sp. grows higher up. Again therefore there is no single "right" number.
  
  See details at DRYWALL MOLD TESTING
• Critical moisture level when painting a building surface:
  
  Experts generally agree that painting surfaces at more than 12% moisture content is likely to lead to a paint failure. There are difficult issues in making such measurements accurately over an entire building surface.
  
  Assessing the paint-ready condition of some materials like stucco is particularly difficult.
  
  See details at PAINT SURFACE PREPARATION
• Critical moisture level in wood:
  
  In assessing the risk of rot or mold growth in wood, (with some variation for wood species) a wood moisture content at 18% or above is considered "wet".
• Critical moisture level in indoor air:
  
  In assessing the level of indoor humidity or humidity target
  
  See details at HUMIDITY CONTROL & TARGETS INDOORS
• Critical moisture level in building ceilings & walls:
  
  In assessing the risk of condensation in building cavities, or insulation, sufficient to cause risk of rot, mold, insect attack, one must consider the dew point, which is not a fixed number
  
  See details at see DEW POINT TABLE - CONDENSATION POINT GUIDE
• Critical moisture levels in chimneys:
  
  In assessing the risk of chimney damage and possible unsafe condition we discuss a combination of factors including duration of moisture
  
  See details at CHIMNEY WET TIME & CORROSION
• Critical moisture levels in fiber cement siding:
  
  In assessing the probability of shrinkage issues in fiber cement siding we found that manufacturers use the phrase "do not install if wet" without giving the slightest help in defining just what they meant by "wet" - doubtless we can thank their lawyers for that smokescreen
  
  See details at SIDING, FIBER CEMENT MOISTURE LEVELS
• Critical moisture levels in wood flooring:
  
  Flooring installers know that even wood floor materials that arrived "dry" from the factory in moisture-tight wrapping must accommodate to the building moisture level before the floor is installed, and even afterwards, if the floor was not installed to allow for movement as building moisture levels vary seasonally the wood floor may buckle or even explode upwards.
  
  See details at FLOOR, WOOD MOISTURE
• Errors in measuring moisture:
  
  Building scientists and home inspectors use moisture meters, RH meters, and a range of instruments themselves subject to errors if not properly used and interpreted
  
  See details at MOISTURE METER STUDY

Question: which moisture meter to use before re-painting T-111 exterior siding

(Mar 28, 2015) Ruth said:

T-1ll exterior siding installed one year ago has developed hairline cracks. According to the manufacturer of Protek Elastoprime the plywood must be thoroughly dry before application of this coating. To determine if the wood is dry enough, which type of moisture meter, if any, do you recommend?

Reply: when, where, how to check for moisture before re-painting

Ruth

I would use a pin type moisture meter for measurements that are principally concerned with the surface or near-surface moisture of the siding.

If I were looking for evidence of a leak deeper in the wall cavity I'd use an electronic type moisture meter.

But take care: I've investigated paint failures at sites where the painter used a moisture meter and asserted that the siding was dry enough to paint. The problem was that she did not make measurements in the best spots: before painting walls on a particular side of the building, measure the locations on that side that are most-likely to need more drying time.

For a comprehensive look at avoiding paint failure take a look at You might want to check this more comprehensive advice on causes of paint failures:

see PAINTING MISTAKES.

Off the cuff, for the case you cite, points at which I'd check for moisture before painting include (as examples as this can't be a comprehensive list):

• areas lowest on the wall
• areas at intersections of trim and siding, especially horizontal trim
• areas that are longest in shade
• areas where stains or other old visual clues suggest there have been paint problems in the past
• areas of the T111 siding that needed repair prior to the paint job.
• the last areas of the T1-11 siding that were primed prior to application of the finish coat - as we want to be sure those are thoroughly dry.

For other readers, more about Protek's Elastoprime, a product designed for restoration of T-111 exterior siding, is at the company's website www.protek-usa.com

Question: how to detect leaks before they do major damage

(Jan 8, 2015) kathy said:

I live in a condo and have had 2 major inside wall leaks in 3 years . I would like to be able to detect the leak before it causes major damage . What device would you recommend

Reply:

Kathy

A more useful answer would need to be based on knowing more about your building, its construction, materials, and leak history - things that an experienced inspector could consider when on-site. But in general, I would not rely on a moisture meter alone to detect leaks.

I'd start with the building leak history to understand where leaks have already occurred, why, and what was done to correct them - and thus I'd ask if the repairs were adequate in extent and quality.

I'd continue with a visual inspection of the building to identify important leak risk points. My view is that this visual inspection is most important since no instrument is completely reliable at determining the presence, age, extent of building leaks.

I'd continue with an assessment for hidden damage where leaks have already occurred.

IR or thermal imaging is used by some inspectors to look for leaks since we can stand back and look at a large area at once, but its efficacy depends on how current the leak is as well as various temperatures and site conditions

Moisture meters that use a pin sensor or that use an electronic signal also only work if moisture is present at the spot where the test is performed.

I worry that by the time you detect a leak using any method you will already be at a point where the wet materials need to be excised as well as the leak repaired.

Please see more-detailed advice at MOISTURE METER STUDY

...

Continue reading at MOISTURE METER STUDY or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Key Moisture Detection Articles

• CHIMNEY WET TIME & CORROSION
• CORROSION in ELECTRICAL PANELS
• DEW POINT TABLE - CONDENSATION POINT GUIDE
• DRYWALL MOLD TESTING
• FLOOR, WOOD MOISTURE
• HUMIDITY LEVEL TARGET
• PAINT SURFACE PREPARATION
• PAINTING MISTAKES
• SIDING, FIBER CEMENT MOISTURE LEVELS
• SWEATING (CONDENSATION) on PIPES, TANKS
• VENTILATION in BUILDINGS
• WATER ENTRY in BUILDINGS
• MOISTURE METER STUDY
  • MOISTURE METER ERRORS
  • MOISTURE METER CHOICES
  • THERMAL IMAGING, THERMOGRAPHY
• WET, DEFINITION OF
• WET SUBMERGED K&T WIRING

Suggested citation for this web page

WET, DEFINITION OF at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING MOISTURE

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