The materials of the light wood wool boards contain cement as a binder. In combination with water contained in humid air, cement gives a strongly alkaline reaction. It makes it, that alkyd varnishes are saponified and become water-soluble.
Veneered interior doors are to be covered with a clear varnish. What test of the substrate should be carried out before applying the coating? Please justify, why this research is necessary
| Research required | Justification |
| Identification of the type of veneer | some types of wood may delay or prevent the hardening of the coating |
| The variety of shades of color | optical defect; may also be a sign of possible internal damage, e.g. damp, if there is a stain on the surface |
| Degree of moisture | high humidity may damage the coating later |
| Stand off the edge of the veneer | may damage the coating later |
| Dirty | optical defect; it can also damage the coating later |
Please justify, why wood-based materials should not be used in external elements that are to maintain constant dimensions?
Wood-based materials cannot be permanently protected in the external environment. For this reason, it is not possible to guarantee a completely defect-free coating. Due to the action of moisture, soluble components of the adhesive in chipboards and plywood can be washed out, which causes stains on the outside and inside of the coatings. Particularly in the case of bonding with alkaline phenolic resins, the formation of white efflorescence is possible.
Otherwise, Wood-based materials swell strongly when they absorb moisture. This causes the surface to crack and the coating to peel off.