How do i deal with the black mold behind the tub surround in my Bathurst bathroom — can i just paint over it with mold-killing primer?

Painting over black mold is not a solution — it's a delay tactic that will make the problem worse. Mold-killing primer is designed to prevent future mold growth on clean surfaces, not to kill or encapsulate an active colony. Whatever is growing behind your tub surround will continue spreading through the substrate even with primer on top.

Here's the reality of what's likely happening in your Bathurst bathroom: moisture is getting behind the surround through failed caulk, cracked grout, or a damaged panel edge. Northern NB's climate — with its cold winters and the humidity swings between seasons — creates ideal conditions for mold to take hold once water finds a gap. The mold you're seeing is almost certainly the surface expression of a larger problem in the drywall or backer board behind it.

The right approach is to pull the surround and assess the damage properly. This means removing the tub surround panels or tile, inspecting the substrate, and determining how far the mold has spread. What you find will dictate the scope of work:

• Surface mold on cement board or tile backer: Scrub with a 1:10 bleach-to-water solution, allow to dry completely (48-72 hours with good ventilation), then apply mold-resistant primer before reinstalling or retiling. Cement board handles moisture well and often survives.
• Mold in drywall: Standard drywall behind a wet area is a code violation in the first place — it should never have been used there. Any drywall with mold penetrating the paper face needs to be cut out and replaced with cement board or moisture-resistant backer.
• Mold in the framing: If it's reached the studs, you're looking at a more significant remediation. Structural lumber with surface mold can sometimes be treated with a borate-based solution (like Tim-bor) and sealed, but badly compromised wood needs to go.

On the health side, "black mold" is a term people use loosely — the genuinely toxic species (Stachybotrys chartarum) is less common than it's feared to be, but any significant mold growth in a bathroom warrants caution. If the affected area is larger than roughly 1 square metre (10 sq ft), Health Canada recommends professional remediation. For smaller areas, a homeowner can handle it with proper PPE: N95 respirator minimum, safety glasses, and gloves. Bag all removed material immediately and dispose of it properly.

Cost-wise, a professional bathroom mold remediation in the Bathurst area typically runs $500–$1,500 for a contained tub surround situation, rising to $3,000–$6,000+ if the framing is compromised or the mold has spread into adjacent walls. A full tub surround replacement with proper cement board substrate and new tile or acrylic panels adds another $1,500–$4,000 depending on materials and scope.

One important note for Bathurst specifically: if your home was built in the 1970s or 1980s, check whether the existing surround contains asbestos-containing materials before you start pulling things apart. Some older vinyl and composite panels from that era did contain asbestos. If you're unsure, have a sample tested before demolition — asbestos testing runs about $30–$75 per sample through a certified lab.

Once everything is clean and dry, the permanent fix is cement board substrate, properly waterproofed seams (RedGard membrane or similar), and silicone caulk — not grout — at all corners and the tub-to-wall joint. Silicone stays flexible and doesn't crack the way grout does under the seasonal movement NB homes experience.

Find a licensed contractor who handles bathroom renovations in the Bathurst area through the New Brunswick Construction Network directory — getting this done right the first time is far cheaper than dealing with it again in two years.