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Woodwork Paper 3, Nov/Dec 2013  
Questions: 1 2 3 4 Main
General Comments


Question 3

  1. State two advantages of casein glue over animal glue.


  1. Name one timber defect caused by each of the following:
  2. drying timber too rapidly;
  3. improper stacking.
  1. State four characteristics of oil varnishes.


  1. Sketch a double ball catch.

Most candidates were able to:

-           name the timber defect that occurs when timber is allowed to dry too rapidly;
-           name the timber defect that occurs due to improper stacking;
-           state the characteristics of oil varnishes.

However, they were unable to:

-           state the advantages of casein glue over animal glue.
-           sketch a double ball catch.




The expected response to question 3 is as given below:

(a)       Advantages of casein glue over animal glue

-           casein glue is prepared cold and used cold, thus allowing a longer assembling-time than animal glue;
-           casein glue is water resistant;
-           assembled job needs not remain in the cramps for tool long as required for animal glue;
-           suitable for external use;
-           heat can be used to accelerate the drying process of casein glue, whereas heat would remelt animal glue;
-           available in various sizes;
-           casein glue is fairly water resistant, whereas water would cause animal glue to stain the surface or glue line.

  1. Timber defects caused by drying too rapidly.


  1. honeycombing, case hardening, collapse; surface splitting; checks.

Timber defect caused by improper stacking.

  1. twisting, bowing, cupping, splits, warping, springing.
  1. Characteristics of oil varnishes


-           dries first by evaporation of the solvents and thinners;
-           cures or hardens by oxidation of the oils;
-           film cures gradually from its outside surface towards the wood;
-           slow drying;
-           cannot be diluted with water;
-           flows smoothly from the brush;
-           has high viscosity;
-           levels out with less tendency to show brush marks;
-           film is tough, flexible and durable.

  1. Sketch of double ball catch

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