Blockboards are engineered wooden boards that are made using softwood blocks for the core and hardwood veneer for the surfaces. The softwood blocks that form the core are actually elongated rectangular strips or battens that are arranged alongside each other across the entire length of the board.
The image below, show the blocks inside a blockboard.
These inside core blocks that make up the major bulk of the blockboard, are dried so as to reduce their moisture content to less than 12%.
For the front and back surfaces, single layers of hardwood ply are commonly used as the face veneer. To make the blockboard stronger, more number of plies can also be attached.
Adhesives such as Urea formaldehyde or Phenol formaldehyde (plastic resin) are used to establish the bond between the outer layers and the core.
The outer layers are firmly pressed over the core blocks, using hot press blockboard machines. These machines generally use steam as the heat source. Because of hot pressing the adhesive fully cures, and the bond becomes stronger.
1. The softwood blocks are obtained by slicing the logs of timber, while the outer veneers are usually obtained by rotary-cutting the logs.
2. For exterior grade blockboards, phenol formaldehyde glue is used as it gives stronger bond.
3. Some manufacturers in rare cases also use harwood blocks for the core. However most common is softwood (e.g. pinewood) for the core.