.2l/°i: 
 
 TECHNICAL     NOTE     number        193 
 
 UNITED    STATES     DEPARTMENT    OF    AGRICULTURE  FOREST     SERVICE 
 
 FOREST     PRODUCTS     LABORATORY 
 MADISON     5.     WISCONSIN 
 
 STARVED   GLUE    JOINTS 
 
 St 
 
 DEPOSITORY 
 
 Many  failures  in  glued  wood  products  are  caused  by  "starved"  joints, 
 or  joints  in  which  the  film  of  glue  between  the  wood  surfaces  is  not  con- 
 tinuous. Starved  joints  are  readily  identified  by  broken  joints  showing 
 little  or  no  wood  failure  or  with  little  or  no  glue  visible.  Such  joints, 
 according  to  the  Forest  Products  Laboratory,  are  not  necessarily  the 
 result  of  a  lack  of  glue  spread  on  the  wood;  heavy  spreads  are  as  likely 
 to  produce  them  under  ordinary  commercial  conditions  as  light  spreads. 
 They  are  caused  rather  by  the  application  of  pressure  to  the  joint  while 
 the  glue  is  too  fluid. 
 
 Starved  joints  are  more  likely  to  occur  with  glues  of  low  viscosity,  such 
 as  warm  animal  glue,  than  with  casein,  vegetable,  and  other  thick  glues. 
 Starved  joints  have  also  been  observed  with  some  of  the  thermosetting 
 synthetic  resin  glues  when  short  assembly  periods  and  heavy  pressures 
 are  combined  with  thin  glue  mixtures.  Such  thin  mixtures  may  result 
 from  use  of  the  mixed  glue  too  soon  after  mixing. 
 
 Some  woods  are  more  susceptible  to  the  production  of  starved  joints  than 
 others.  Birch,  maple,  red  oak,  and  ash,  which  have  open  pores,  ab- 
 sorb glue  from  the  spread  in  such  considerable  amounts  that  they  often 
 leave  the  joints  starved.  Basswood  and  yellow-poplar  also  take  up  a 
 great  deal  of  gluet  but  weak  joints  are  not  very  noticeable  in  these  woods 
 because  the  woods  themselves  are  weak.  Other  woods  with  smaller  cells 
 open  to  the  gluing  surface  do  not  seem  to  be  so  subject  to  starved  joints. 
 
 In  some  cases  starved  joints  may  result  from  the  use  of  wood  containing 
 too  much  moisture  at  the  time  of  gluing.  This  has  been  observed  fre- 
 quently in  the  use  of  phenol-resin  film  glues  and  is  likely  to  occur  when- 
 ever wet  wood  is  glued. 
 
 To  avoid  starved  joints  it  is  necessary  to  mix  a  glue  solution  thick  or  to 
 allow  it  to  thicken  in  the  pot  or  on  the  wood  before  pressure  is  applied. 
 When  it  is  necessary  to  glue  under  conditions  that  might  produce  starved 
 joints,    the  use  of  light  pressure  is  advantageous. 
 
 ZM767  73F  Agr!cultur#-IUdlion 
 
UNIVERSITY  OF  FLORIDA 
 
 3  1262  09216  7567