Cedar Stain (Tannic Acid Bleed): Vancouver Painters

www.vancouversbestpainters.com teaches us that stains on cedar and redwood are due mainly to moisture and insufficient or improper priming.  The resins in certain types of cedar, redwood, and mahogany bleed through paint.  Moisture carries water-soluble colour extractives (tannic acid) contained in the wood through the film.  Staining is more visible when light or medium colours are used.

Two patterns of tannin bleed can occur;  their appearances indicate the source of the moisture.  Rain, dew, humidity, or faulty roof drainage cuase water to penetrate the paint film from the front of siding, crating diffused discoloration.  Water-based house paints also can leach out tannic acid and cause diffused discoloration.  Rundown or streaky discoloration occurs when water finds its way behind the siding.

Solution For Cedar Stain

First, the source of moisture should be located and corrected.  Remove loose or cracked caulking and repair with a quality product.  Avoid caulks that can crack, shrink, or lose adhesion.  Clean out nearby gutters and downspouts.  Wash the stained surface with a commercial-grade bleach solution , rinse with a pressure washer, and allow the surface to dry thoroughly for at least 48 hours.

Prime the dry wood.  Special water-thinned primers formulated to seal in stains are available; alkyd oil based primers are recommended by some manufacturers, as are some acrylic latex stain-blocking primers.  In cases of sever staining, use two coats of primer before topcoating.  A waiting period of at least 48 hours after application is recommended before applying the second coat and or the finish coat.

Most tannic acid stains will penetrate the first coat of primer in seven days, leaving a brownish spot or ring.  If tstains do appear, re-prime the stained spot, allow it to dry thoroughly, and apply the finish coat.  It is a good idea to prime board or siding shingle edges and ends.  If possible, backprime prior to installation.  These procedures will forestall moisture from entering the wood.  If staining occurs during application, sand lighly and re-prime before applying the final finish.

Rick Anderson  www.vancouversbestpainters.com www.604painters.com www.vancouverindustrialpainting.com