How do I properly undercut door casings for a flush flooring installation in my older NB home with plaster walls?

Undercutting door casings allows your new flooring to slide underneath for a clean, professional appearance without visible gaps or transition strips. This technique is essential in older NB homes where thick plaster walls and substantial trim work make removing and reinstalling casings impractical.

The Right Tools Make All the Difference

Use an oscillating multi-tool with a wood cutting blade for the cleanest cuts in NB's older hardwood trim. These tools vibrate rather than rotate, preventing the aggressive action that can crack brittle old paint or loosen plaster around the casing. A manual undercut saw (Japanese pull saw) works for small jobs but requires steady hands and patience. Avoid circular saws or reciprocating saws near plaster walls — the vibration can crack the plaster or damage the wall-to-trim connection.

Set your cutting depth to match your new flooring thickness plus underlayment. For laminate or LVP with foam underlayment, this typically means 10-12mm total. For engineered hardwood, measure the actual plank thickness — it varies from 8-20mm depending on the product. Always cut 1-2mm higher than your measurement to ensure the flooring slides easily without binding.

Protecting NB's Plaster Walls

Older NB homes often have horsehair plaster that's become brittle after 60-100 years. Before cutting, score the paint line where the casing meets the wall using a sharp utility knife. This prevents paint from chipping or peeling beyond your cut line. Place painter's tape along the wall above your cut line for additional protection.

Work slowly with light pressure — let the tool do the work rather than forcing it. The oscillating action cuts through multiple paint layers and old-growth lumber gradually. Rushing leads to tear-out, especially where the grain changes direction in mitered corners.

Managing the Mess

Undercutting creates fine sawdust that settles into every crevice. Tape plastic sheeting over heating vents and use a shop vacuum with a brush attachment to collect dust as you work. In homes with forced-air heating, this prevents sawdust from circulating through your ductwork for months afterward.

Special Considerations for Maritime Conditions

NB's humidity cycles cause wood trim to expand and contract seasonally. If you're installing flooring during the dry winter months (October through April), the casings may be at their most contracted state. Leave an extra 1mm of clearance to account for summer expansion — this prevents the flooring from binding when humidity returns in June.

When to Hire a Professional

Consider professional installation if your home has intricate Victorian-era trim, carved casings, or if you discover asbestos-containing caulk around the trim (common in pre-1980 NB homes). Professionals have specialized tools for complex cuts and experience protecting valuable heritage millwork. For standard ranch or colonial trim in homes built after 1960, this is a manageable DIY task with the right tools and patience.

Need help finding a professional flooring installer who's experienced with older NB homes? New Brunswick Flooring can match you with contractors familiar with heritage home challenges.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• FRS Flooring Solutions
• M&L Commercial and residential services
• Thirty Four Renovations
• Gionetterenovations
• Forever Epoxy Inc