Standard Operating Procedure Wood Protection Group


Name: Water Absorption and Thickness Swell

Date: September 18, 2000

SOP #: 330

Revision: 3

Author: Erik D. Keranen\

Supercedes: Revision 1,2

Approved: Glenn M. Larkin\



Scope: This SOP covers specimen preparation, treatment, and measurement for the 2-hour water soak, 24-hour water soak, and non-recoverable thickness swell determinations.


1.       Preparing and measuring the specimens (SOP 330 Form A-Water Soak Data Sheet For 75 x 75 mm Specimens, or SOP 330 Form B-Water Soak Data Sheet for 25 x 25 mm Specimens)

1.1        Cut the test specimen to 75 x 75 mm in size, or per project protocol.

1.2        Condition the specimen in chamber #2 for two weeks.

1.3        Weigh the specimen to the nearest 0.01 grams. Record the data.

1.4        Measure the specimen width, length and thickness to the nearest 0.1 mm. Thickness is measured at the four points 25 mm in from each side at the corners. Use a template for speed and accuracy to mark each measurement point. Record the data and average the four thickness measurements from each specimen for thickness swell calculations.


2.       Preparing the water tanks and submerging the specimen

2.1        Clean the water soak tank of dust and debris.

2.2        Place tank in a temperature controlled room at 18+/- 1 C.

2.3        Hang the specimen hold-down grate on its side hooks in the tank. Ensure that the tank and grate are level.

2.4        Close the tank drain valve. Use a garden hose to fill the tank with tap water to one inch over the bottom of the hold-down grate.

2.5        Condition the water to a constant temperature of 18 +/- 1 C.

2.6        Submerge the specimens horizontally under the hold-down grate.

2.7        Record the date and time the specimens are submerged.


3.       Obtaining 2-hour, and 24hour water absorption and thickness swell

3.1        After two hours remove the specimens and stand them on edge in a sink for about ten minutes. Pat the specimen surface with a paper towel to remove excess water. Weigh the specimen and obtain the four thickness measurements. Record all data.

3.2        Re-submerge the specimens. Record the time of re-submersion.

3.3        After an additional 22 hours from the time of re-submersion remove the specimens from the water and repeat step 3.1 to obtain 24-hour water soak data.

3.4        Record the ovendry weight.


4.       Calculations

4.1        Determine the 2-hour thickness swell, 24-hour thickness swell, and non-recoverable thickness swell of each specimen using the following formulas:


TS 2-hour = (T2hTic) / Tic * 100

TS 24-hour = (T24hTic) / Tic * 100


TS non = (TfrTic) / Tic * 100


Where: TS = % Thickness swell,

T2h = Specimen average thickness after 2 hours submersion,

T24h=Specimen average thickness after 24 hours submersion,

Tfr = Specimen average thickness after final reconditioning, Tic = Initial conditioned specimen average thickness


5.       Reconditioning specimen for non-recoverable thickness swell determination

5.1        Place the specimens in an airflow hood for at least two weeks to approach the pre-soaked original weight.

5.2        Place the specimens in humidity chamber #2 for an additional two weeks to fully recondition to approximately 12% moisture content.

5.3        Record the final weight and thickness measurements.


6.       Obtaining Ovendry Specimen Weight

6.1        Place specimens in an oven at 103C for 48 hours.

6.2        Determine the 2-hour water absorption and 24-hour water absorption for each specimen using the following formulas:


WA 2-hour = (Wt2h-Wtic) / Wtic *100


WA 24-hour = (Wt24h-Wtic) / Wtic *100


Where: WA = % Water absorption,

Wt2h = Specimen weight after 2 hours of water submersion,

Wt24h =Specimen weight after 24 hours of water submersion,

Wtic = Initial conditioned specimen weight


6.3        Calculate the specimen moisture content after the initial conditioning, and at the time the fully reconditioned specimen measurements are taken:


MCinitial = (Wtic Wtod) / Wtod *100


MCfr = (Wtfr Wtod) / Wtod *100



Where: MC = Moisture content (% oven-dried basis),

Wtic = Initial conditioned specimen weight,

Wtod = Oven-dried specimen weight, and

Wtfr = Final reconditioned specimen weight





Annual Book of ASTM Standards, D 1037 Standard Methods Of Evaluating the Properties of Wood-Base Fiber and Particle Panel Material, 1989, pp. 167-196.