Peeling From Mill Glazed Western Red Cedar

  PEELING FROM GLAZED WESTERN RED CEDAR OR REDWOOD SIDING

Mill-glaze is a hard, varnish-like glaze that appears on smooth, flat-grained Western Red Cedar and occasionally on redwood.

There is controversy over the exact cause of mill-glaze, but the general belief is that it is caused by planing and/or drying the lumber. During the milling or planing process, overheating of the flat-grained, smooth siding may bring water soluble resins to the surface, creating a hard, varnish-like glaze. Mill-glaze problems normally occur when siding has been installed smooth side out.

Solution

If the surface is unpainted, the best system is one that uses three coats, consisting of one coat of primer and two coats of latex finish. The most important feature of the system is the primer. It must be one that seals in tannic acid and prevents extractive bleeding. If, after one coat of primer dries, a brownish stain forms on the surface, an additional coat of primer must be applied to seal in the stains in the affected areas. Allow the first primer coat to dry before re-priming. If no additional stains are present, apply two coats of a high-quality latex finish.

For repainting over mill-glaze problem areas, remove the coatings either by pressure washing or hand scraping. Apply primer as indicated above and finish with two coats of latex finish.

Newly-installed siding should be finished as quickly as possible. Ultraviolet rays from the sun tend to degrade the integrity of the wood’s surface. A 50% loss in adhesion occurs on Western Red Cedar weathered for 16 weeks prior to finishing.

Abrading the mill-glaze surface by sanding prior to painting will ease surface tension and provide a better surface for the initial primer coat.

This article prepared by Rick Anderson of www.vancouversbestpainters.com call: 604-PAINTER