Black marks appearing on new deck recently painted with brown oil base stain?


New deck installed, painted with brown oil base stain. Now I see black marks appearing. What is this?

2 Responses

  1. If the marks appear near nails or screws then they could be caused by rust or the galvanized coating. If away from metal parts, then it could be tannin bleed or wood sap.

  2. The appearance of black marks on a new deck recently painted with brown oil-based stain can be attributed to several factors. One common cause is mold or mildew growth, often seen in humid or shaded areas where moisture accumulates. To address this issue, thoroughly clean the affected areas with a mild detergent and water solution or a specialized deck cleaner that targets mold and mildew. Additionally, consider applying a mold-resistant sealant or fungicide before recoating the deck with a fresh coat of stain.

    Galvanized nails or screws can also cause a chemical reaction with the wood and water. Producing an expanding dark spot. The only way to get rid if this spot is to use a wood brightener or wood bleach on the spots then restain.

    Another possible reason for the black marks is tannin bleed from the wood itself. Some wood species, such as cedar or redwood, naturally contain tannins that can bleed through the stain, causing discoloration. To prevent this, use a stain-blocking primer before applying the oil-based stain to create a barrier against tannin bleed.

    It is also essential to ensure that the deck was properly prepared before staining. Any residual dirt, grease, or previous coatings on the wood can interfere with the adhesion of the stain, leading to discoloration or black marks. Before staining a wood deck, thoroughly clean and sand the deck surface to remove any contaminants and create a smooth, even surface for the stain to adhere to.

    Lastly, consider the quality and compatibility of the oil-based stain used. Lower-quality stains or mixing different types of stains can result in inconsistent color or discoloration. Always follow the manufacturer’s instructions for proper application and allow sufficient drying time between coats to ensure a uniform finish.

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