Failures on Wood: Checking versus Cracking
Checking and Cracking are both typical paint failures on wood surfaces. Checking (pictured above) describes the formation of small, narrow breaks in a coating film that do not extend to the underlying surface, and is often seen on wood where the previous coatings have become hard, brittle, and unable to expand and contract with the substrate.
Some common causes are:
- coating was applied too thickly, limiting its flexibility
- coating was applied during excessively high temperatures, causing the coating to cure too rapidly
- coating was applied to a soft or uncured primer
- applied coating was overspread and overthinned
- moisture ingress caused the wood substrate to expand
The term ‘checking’ is also used to describe the delamination of plywood, where water intrusion softens the adhesive between the individual plies that comprise the plywood, causing the individual layers to lift and separate.
Cracking (pictured above) also appears as lines or breaks in the dry paint film, but these extend to the substrate or coating below. With wood, the most frequent cause is expansion from moisture gain (when water infiltrates the wood substrate after painting); wood shrinkage from moisture loss(if wood had too high a moisture content prior to painting); or physical distortion such as occurs with cupping or crowning. Cracks can also appear from coating shrinkage when high PVC(pigment volume concentration) paints are applied in overly thick films.
Other common causes for cracking include: coating was applied too thickly or applied/cured at too high a temperature; or coating was overspread and overthinned. Cracking can also occur from:
- using a low quality, inflexible paint
- coating an unprimed surface
- excessive hardening of an aging paint
- excessive film build from too many coats of paint
— Excerpted from MPI’s Identifiers: Defects and Failures book. For details or to order a copy,
click here |
|
This Just In: New MPI Listing Manufacturers
Anchor Paint Manufacturing
Anchor Paint (Tulsa, OK) now has approved products with MPI.
Click here to see their complete list of MPI Approved Products.
Founded in 1962, Anchor Paint specializes in manufacturing custom-formulated products for the industrial, OEM and architectural markets. Geographical distribution is the US and international.
Jotun UAE Ltd.
The Jotun Paints offices in the Middle East & North Africa now have a primer and textured coatings approved with MPI.
Click here to see their complete list of MPI Approved Products
Founded in 1926 in Norway and one of the world’s leading paint manufacturers, Jotun established its presence in the Middle East in 1974. One of the first manufacturers to be awarded the ISO 14001 certification and OHSAS 18001, Jotun manufactures decorative, protective, and marine paints with geographical distribution across the Middle East & North Africa.
Modern Masters
Modern Masters (Sun Valley, CA) now has an approved product with MPI. Their Colorfast Bold and Vibrant paint meets the requirements for MPI # 10 Latex, Exterior Flat (MPI Gloss Level 1-2)
Founded in 1962, Modern Masters Inc. manufactures architectural, specialty, OEM and theme coatings. Their products are sold globally through distributors and independent paint dealers.
Revisions to MPI Standards
- MPI #3 Primer, Alkali-Resistant, Water Based: change in adhesion requirement. Click here to order the updated standard.
|
.jpg)
