7.0) Water (drying): (page 3 of 5)

7.14) Porosity as a Drying Guide: The porosity or permeance of building and contents material should be used as a guide when determining the number of dehumidifiers needed to capture wicked moisture from a room or structure.  This is based on the surface tension (capillary) of a material and air movement, and is the determining factor on the rate of wicking water.  Moreover, the correct combination of dehumidifiers to airmovers is crucial.

As described in Section 7.13, the porosity of materials is based on its permeance factor, and is rated as highly porous, semi-porous, or non-porous. 

When calculating the number of dehumidifiers needed, the overall moisture content; (atmospheric, structural components and content items), and the permeance rating of the materials’ surfaces should be used to determine the dehumidifiers size and number of air changes per hour:

    - Highly porous …………. 3 air changes per hour
    - Semi-porous …………... 2 air changes per hour
    - Non-porous ……………. 1 air changes per hour

When applying restorative drying principles, technicians should couple the psychrometric principles found in Section 7.10 and the materials porosity (what is wet, and how wet is it) and classify the wet areas as outlined in Section 7.42.

7.15) Moisture Content: Interior atmospheric humidity could be considered ideal when its relative humidity is between 30% and 40% at 70º F.  While ASHRAE 62-1989, 5.11 states “high humidity can support the growth of pathogenic or allergenic organisms moisture” --- and recommends that humidity in habitable spaces, preferably, should be maintained between 30% and 60%. 

Certain building components, such as wood framing can expand when wet or moist and fail prematurely from decay if not properly dried.  The expansion of wood framing lumber can cause wallboard nails and screws to pop, as well as stress cracks.

When performing restorative drying after water losses, the moisture content of certain building components and content items should be monitored and reduced to acceptable levels as shown in Table 7-B.
 

Building Component & Furnishing Moisture Levels
Source: William Yobe & Associates
& U.S. Forest Products (USDA)
Table 7-B

Acceptable moisture levels for building materials should be the moisture level manufacturers specify for storing materials, or the manufacturers recommended moisture content for materials before installation.

7.15.a) Dry Standard: The term "dry standard" should not be confused with the terms "moisture content" or "drying goals."

The term dry standard should pertain to the structures non-affected dry areas as they relate to the structures present operating moisture content. 

Moreover, "dry standard" as phrased above, should not be used as a drying goal.  Reason being, the structures HVAC system  may not be properly sized or balanced or may be neglected.  Or the building envelope may be improperly designed or installed or may be neglected, resulting in the structures HVAC system not producing a net-positive pressure, resulting in infiltration (i.e., moisture gain).

Moisture Gain = Leakage + Diffusion + Internal
Source: NIOSH

When a structure has higher than normal moisture content within building components or content items in non-affected areas, the building owner or facility manager should be informed.

7.16) Wood Moisture: Wood contains moisture, and the percentage of the wood’s moisture content fluctuates with the relative humidity, for wood is constantly exchanging moisture with the atmosphere.  This is due to the hygroscopic nature of wood.    

Wood for drying purposes, could be classified into two categories; structural and contents, while their surfaces should be broken down into; finished and non-finished. 

The moisture content change of non-finished wood is slow, while the moisture content change of finished wood is quit slower, since the moisture has to diffuse through the surfaces’ protective coating.

Vapor pressure exerts pressure on the wood surface.  For wood or other surface materials to dry, the capillary action at the surface of the material would have to increase.  This is accomplished through reduced vapor pressure (heat) and grains of moisture reduction (air exchanges and dehumidification).

7.17) Heat & Drying: Heat plays an important role in the drying process.  As stated in Section 7.11.a, the temperature could be considered the balance point of a drying system, since heat reacts with moisture to create kinetic energy.  Creating a vapor pressure differential at material surfaces induces the expansion of materials and allows for a faster release of moisture into the atmosphere, and the appropriate number of air changes is needed to prevent secondary damages.

Over the past few years, several firms have developed heat systems for structural drying and for indoor air quality (IAQ) issues as further described in Section 7.43.
 

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7.18) AC Systems & Drying: AC (air conditioning) systems are designed to reduce interior moisture levels during hot, humid summer months, and this is accomplished through the dehumidification characteristics of air conditioning.  However, according to Dr. Lstiburek in his publication Builder's Guide Hot-Humid Climates; "... dilution ventilation during the winter and air conditioning during summer will not be able to control interior moisture levels in hot-humid climates without supplemental dehumidification.”  Furthermore, Dr. Lstiburek states “Air conditioning will only remove moisture from the interior air when the air conditioning system is cooling the air.  If there is not much need (demand) for cooling, dehumidification by the air conditioning system will not occur.  Again, under such conditions a dehumidification system is needed and can be supplied by a stand alone dehumidifier or a ventilating dehumidifier.”

The Builder's Guide Hot-Humid Climates also states in Chapter 10 that air changes will not remove moisture, however, this statement is for a buildings HVAC systems, and should not be taken out of content, for heat and dry air, when designed as a drying system, will release moisture, and air exchanges are a critical part of a drying system when using heat or dry air as further described in Section 7.43.
 

Dehumidifier Selection Chart
Source: Dri-Eaz Products, Inc.
Table 7-G
 

7.19) Recommended Drying Levels: The determination of what moisture content building materials should be dried to is determined by building material manufacturers and standard setting organizations, while the moisture content (humidity) of the buildings interior atmosphere is determined by ASHRAE (American Society of Heating and AC Engineers).

Paint manufacturers (Sherwin Williams and Glidden) state that their products (latex paint and primers) should be applied over dry gypsum wallboard (drywall) with a moisture content of 12% or less. 

Carpet manufacturers and flooring tile manufacturers state that their products should be installed over concrete with a moisture content of 5% or less, or over concrete that has a moisture content of .75 RH at 70° F when performing a Hygrometer or Relative Humidity Test. (ref. 7.20)

The Wood Handbook, published by the U.S. Forest Products Laboratory --- Division of the U.S. Department of Agriculture states in Chapter 12, that: “Softwood lumber intended for framing in construction is usually targeted for drying at an average moisture content of 15%, not to exceed 19%.  Softwood lumber for many other uses is dried to a low moisture content, 10% to 12% for many appearance grades to as low as 7% to 9% for furniture, cabinets, and millwork”.

Additional moisture content levels can be found in Section 7.15 and Table 7-B.

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Extracted from the Loss Recovery Guide with Standards (LRGS)
© Copyright 1998-2008 William Yobe

Find It Fast - With The ... LRGS - Navigational Index


 

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7.20) Concrete Drying: Interior concrete should have a moisture content of .75 Rh at 70° F when performing a hygrometer or relative humidity test per ASTM – Designation: E 1907-97, Standard Practices for Determining Moisture-Related Acceptability of Concrete Floors to Receive Moisture-Sensitive Finishes.

Concrete takes longer to dry than gypsum wallboard (drywall) and wood framing lumber due to the capillary nature of the materials, or the longer it takes something to absorb moisture, the longer it takes to dry it. Moreover, concrete requires a pressure - differential to dry, which is best achieved through heat and air changes.   

Heat drying systems or heat produced by dehumidification equipment  should produce the required pressure differential when used in combination with air movers or negative air machines.  Moreover, the drying process should be monitored on a daily basis to assure the appropriate pressure differential is maintained throughout the drying process. For additional information on Heat Drying Systems see Section 7.43.

7.21) Plaster and Gypsum Wallboard: Water and moisture can have adverse effects on plaster and gypsum wallboard (drywall), these effects, whether permanent or reversible, would be dependent on several variables; Category of the water, moisture content, timeframe the drywall is wet, temperature and expansion.

Gypsum wallboard (CaSO₄ 2H₂O) is constructed from calcium sulfate and is chemically combined with water of crystallization, which makes up 20% of its total weight and accounts for its fire resistance rating. 

Excess water and moisture (13% to 90% relative humidity) can cause drywall and plaster board to expand and crack at its joints, and decompose when not treated in a timely and proper fashion. 

When water or moisture has affected the fire rating of drywall, or caused drywall or plaster to lose its self-restraint, it shall be replaced.

When mold (fungi) is buried within materials and inaccessible to chlorine or disinfectants, the mold infested materials should be replaced. Mold forms on drywall due to the organic properties of its paper face. 

When drying drywall or plasterboard, wall cavities should be inspected and remediated when affected with mold (fungi).

It is typical to remove wet drywall before and during the drying process, which is most common when large surface areas are wet, and the removal of wet drywall should reduce drying time.

Wallboard before decorative finishes are applied, would be rated as highly porous and have a permeance factor of 35.3 to 30.2, dependent on its size and ratings as outlined in Table 7-A.

Wall decorations have varying affects on gypsum wallboard and could effect drying methods and drying time. 

Drywall used in residential homes is generally installed horizontally and sized at 3/8" or 1/2".  Drywall and plasterboard used in commercial and institutional facilities is generally installed vertically and sized at 1/2" or 5/8", and could be fire-rated.  Modern plaster applications used in schools and hospitals are generally a plaster - veneer installed over blueboard.

7.22) Floor Coverings: The mitigation of floor coverings would be dependent on the surface material and the severity of soil deposits. 

Carpet could require extracting.  Resilient, hardwood and tile floors could require mopping, sweeping, and cleaning.  While the same process could be required at the offset of the mitigation process to remove possible fallout of contaminates, silts, etc.

Carpet: When wet, carpets should be extracted, and possibly lifted for drying. When approved by the owner, an approved disinfectant maybe applied.  Disinfectants when applied to carpeting, could void the carpet manufacturers warranty.

Hardwood: Heavy soil deposits should be removed, then the floor should be cleaned with a mild non-abrasive detergent.

Resilient and tile flooring: Heavy soil deposits should be removed, then the floor should be  cleaned with a mild non-abrasive cleaner.

Marble: Heavy soil deposits should be removed with care so not to scratch the marble surface.  Then a mild non-abrasive neutral pH cleaner should be used.  Cleaners containing acid or bleach should be avoided.  Marble is crystallized limestone and will etch or discolor when a high pH (alkaline) cleaner is used.

Granite: Heavy soil deposits should be removed with care so not to scratch the granite surface.  Then a mild non-abrasive cleaner with a neutral pH should be used.  Granite is a hard igneous form rock with incredible endurance.

When mitigating a structure after a water loss, the severity, category, source, etc. would determine the proper mitigation procedures.
 

7.22.a) Hardwood Flooring: The water or moisture source can be detected by observing the wood strip formation.  Hardwood flooring strips will cup or crown away from the moisture/water source.  When wood strips are cupped upwards, the moisture/water was absorbed from the bottom of the floor, while hardwood strips that are crowned down are absorbing moisture/water from the top of the floor.

Airmovers (forced), or injection drying (pressure) and dehumidifiers should be set-up and running when wood floor surface moisture conditions are at 11% or higher.

Effective hardwood floor drying could require the removal of the baseboard at opposite ends of the room, perpendicular with the wood strips as described in Sections 6.26 and 6.26.a. 

An expansion joint should be accessible after the baseboard is removed.  Should an expansion joint not be available, technicians could be required to create one by cutting a 3/16" strip along both walls to allow airflow.  Then airmovers using turbovents could be used to force air through the tongue and groove (T&G) as found between the wood strips. 

Hardwood flooring could require refinishing after drying.

When replacing or repairing wood floors, visit the p1m.com Wood Flooring; Grade, Nail & Waste Allowance Charts.

7.22.b) Carpet & Upholstery Cleaning: Carpet and upholstery, when cleaned after a water loss, should conform the following IICRC publications:

IICRC S100 Standard and Reference Guide for Professional Carpet Cleaning
IICRC S300 Standard and Reference Guide for Professional Upholstery Cleaning
IICRC Reference Guide for Inspection of Textile Floor Covering

7.23) Sub-Flooring: Sub-flooring is susceptible to distortion and microbial growth.  The material composition of the sub-floor, the water classification and the moisture exposure time would be useful when determining drying procedures. 

Sub-flooring materials could be; 1x-pine boards, plywood, wafer board, concrete board, etc.

The drying of sub-flooring could require access (ventilation) holes when needed. (ref. 7.24.b)

7.24) Access Holes: Access holes could be required when relieving water and accessing hidden damages.

When providing access holes, they should be sized to achieve the disciplinary action at hand, and once that size is achieved, access demolition stop.

Rough and sharp edges should be removed or covered with a protective means.

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