How do I identify and fix a rotted subfloor section under old linoleum in a 1950s Campbellton home?

Rotted subfloor under old linoleum in a 1950s Campbellton home is a serious but fixable problem — the key is identifying the full extent of the damage before you start cutting, and testing that old vinyl for asbestos before you touch it.

Campbellton sits in one of the most moisture-challenged corners of New Brunswick. The Restigouche River valley creates persistent ground moisture, the heating season runs long and hard, and older homes from the 1950s were built with subfloor assemblies that were never designed to handle decades of moisture cycling without maintenance. Rotted subfloor sections are common in this housing stock, particularly under kitchens, bathrooms, and entryways where water has had years to work its way through worn or failed linoleum seams.

Stop Before You Touch That Linoleum

Vinyl sheet flooring and floor adhesive from pre-1986 NB homes — and 1950s Campbellton homes fall squarely in this category — commonly contain asbestos. This is not a maybe. Before you cut, scrape, pry, or sand anything, send a sample to a certified lab for testing. Asbestos testing costs $25-$50 per sample and takes a few days. If the material tests positive, you need a licensed abatement professional to handle removal — full stop. Disturbing asbestos-containing linoleum releases fibres that cause serious, permanent lung damage. This step is non-negotiable.

If the material tests clean, you can proceed with removal yourself.

Identifying the Full Extent of the Rot

Once the linoleum is safely removed, the real detective work begins. Don't assume the rot is limited to the soft or discoloured area you noticed from above. Rot follows moisture pathways, and in a 1950s home, that moisture has often been travelling along joists, through the subfloor, and into adjacent areas for years before it became visible.

Use a sharp awl or screwdriver and probe systematically — press the tip firmly into the subfloor every 6-8 inches across the suspect area and well beyond it. Sound wood resists the probe; rotted wood accepts it with little resistance and may feel spongy, crumble, or smell musty. Mark every soft spot with chalk or tape. It's common to find that what looked like a 2-square-foot problem is actually 8-12 square feet once you probe honestly. Check the joists below through the basement or crawl space if accessible — if the rot has reached the joists, this becomes a structural repair that requires a building permit and may need a contractor.

Moisture readings matter here. Before you patch anything, use a pin-type moisture meter on the surrounding subfloor. Wood subfloor should read below 19% moisture content before new flooring goes over it. Anything above that means the moisture source hasn't been resolved — and patching over an active moisture problem just delays and worsens the failure.

Making the Repair

For a contained rot section that hasn't compromised the joists, the repair process is straightforward. Cut out the damaged subfloor using a circular saw set to the exact depth of your subfloor panels — typically 5/8 or 3/4 inch in 1950s construction. Cut to the centre of the nearest joists on each side so your patch has solid bearing. Remove the rotted material completely, treat the exposed joist faces with a borate-based wood preservative (Tim-BR-MART and Home Hardware locations in the Campbellton area carry these), and allow everything to dry fully.

Install your patch using 3/4-inch tongue-and-groove plywood (exterior grade, not interior) fastened with screws — not nails — every 6 inches along the joist bearing. Fill the seams with floor patching compound and feather them flat. The patch surface must be within 3/16 inch of the surrounding subfloor height over any 10-foot span before new flooring goes down.

Choosing New Flooring for This Location

For a Campbellton kitchen or bathroom where this rot likely occurred, luxury vinyl plank (LVP) with a stone polymer composite (SPC) core is the most sensible replacement. It's 100% waterproof, handles the humidity swings of a northern NB heating season without expanding or contracting significantly, and costs $5-$12 per square foot fully installed. If the rot was in a bathroom, add a proper waterproofing membrane under any tile work.

Do not reinstall sheet vinyl over a patched subfloor without addressing why the moisture got in — whether that's a plumbing leak, failed caulking, or a drainage issue at the foundation. The patch will rot again within a few years if the source isn't fixed.

When to Hire a Pro

If your probe reveals that rot has spread to the floor joists, call a contractor before proceeding — structural joist repair requires a building permit in NB and goes beyond a flooring project. Similarly, if you find mould alongside the rot (black, green, or white fuzzy growth), professional remediation is the right call before any repair work begins. And again — if that linoleum tests positive for asbestos, licensed abatement professionals handle the removal.

For the subfloor patch itself, a competent DIYer with basic carpentry skills can handle a contained section. For anything larger than about 20 square feet, or if the layout is complex, getting a flooring or renovation professional involved saves time and ensures the patch is properly supported.

New Brunswick Flooring can connect you with local professionals in the Campbellton area if you need help assessing or repairing the subfloor before your new flooring goes in — the matching service is free. Find contractors through the New Brunswick Construction Network directory at newbrunswickconstructionnetwork.com/directory?trade=flooring.