Garage Conversion Plasterboarding and Full Skim by a Plasterer in Barnet

This project involved a detached residential property in Barnet, EN5, where the homeowner had decided to convert an attached single garage into a usable habitable room. The garage was a standard single-width brick-built structure with an existing concrete floor, a side window opening, and exposed timber roof joists. Before any plastering work could begin, the space needed to be fully cleared of stored items and lined from scratch — there were no existing plaster surfaces, just bare brick walls and an open timber-framed ceiling.

As visible in the before photographs, the garage was packed floor to ceiling with household storage — wheelie bins, suitcases, cardboard boxes, shelving units and general clutter filled the entire footprint. The walls were bare brick throughout, with no insulation or lining boards in place. The ceiling area showed exposed timber joists with no plasterboard fixed. There was a single window on the side elevation, and the concrete floor was bare and unfinished. Electrical first-fix cabling was visible hanging from the ceiling area, indicating the electrician had already run cabling ahead of the plastering stage. The space had no plaster on any surface whatsoever.

The full scope of work for this garage conversion plastering project in Barnet covered complete dry lining of all four walls and the ceiling using a timber stud and metal track framing system, followed by fixing of 12.5mm plasterboard throughout, and finally a two-coat multi-finish skim applied to all boarded surfaces. Specifically, the work included: erecting a perimeter timber and metal stud framework fixed to the brick walls at a consistent depth to create flat, true surfaces ready for boarding; fixing 12.5mm tapered-edge plasterboard sheets to the timber ceiling joists and stud walls using drywall screws at 300mm centres; taping and jointing all board joints and internal angles with scrim tape and bonding compound; applying a PVA bonding wash to all plasterboard surfaces prior to skimming; applying a scratch coat of Thistle Multi-Finish plaster across all walls and the ceiling; and finishing with a tight trowelled second coat to bring all surfaces to a smooth, paint-ready standard. Electrical back boxes were cut in and plaster was carefully worked around the first-fix cabling drops. The skirting boards were also fitted prior to the final skim coat, with the plaster taken down neatly to the top edge of each board.

Before plasterboarding could begin, the garage was fully cleared of all contents by the homeowner. Timber sole plates and head plates were fixed to the concrete floor and ceiling respectively, and vertical timber studs were positioned at 600mm centres around the perimeter of all four walls. Metal angle bead was fixed to all external corners. The ceiling joists were checked for level and where any minor variation was found, packers were inserted before the boards were fixed. All board joints were reinforced with fibreglass scrim tape and filled with a bonding coat, then allowed to dry fully. A diluted PVA solution was applied to all plasterboard faces and allowed to become tacky before the first skim coat was applied.

Once the PVA wash had reached the correct tacky stage, the plastering began with the ceiling. Thistle Multi-Finish plaster was mixed to a firm but workable consistency and applied to the ceiling plasterboard in a tight scratch coat, spread evenly using a wide plastering trowel and feathered into the wall angles. The wall surfaces were then tackled in sections — starting from the top of each wall and working downward — with the scratch coat applied at approximately 2–3mm thickness across all four wall faces. Once the scratch coat had firmed sufficiently, a second finishing coat was applied and trowelled to a tight, flat surface. The trowel was dampened periodically to help close the surface and remove any drag marks. Internal angles between walls and between walls and ceiling were ruled straight using an angle trowel, producing clean, sharp junctions throughout. The window reveal was also boarded and skimmed to match the surrounding wall faces. Electrical back boxes were set flush with the plasterboard face before skimming, and the plaster was worked carefully around each one. The finished surfaces were left to dry naturally before the skirting board joints were filled and the room was handed over paint-ready.

The principal challenge on this garage conversion in Barnet was achieving flat, plumb wall surfaces against the existing brick, which had an uneven face across several sections. The brick course heights varied and the mortar joints protruded in places, meaning a simple dot-and-dab boarding approach would have produced undulating surfaces. Additionally, the existing concrete floor was not level, which complicated the positioning of the bottom track and required careful measurement to ensure the stud frame rose truly vertical rather than following the floor line. The ceiling joists also ran parallel rather than at right angles to the longest wall, creating a slightly awkward boarding direction that required additional noggings to be fitted.

To overcome the uneven brick substrate, a full independent timber stud frame was built off the walls rather than fixing directly to the masonry. This allowed each stud to be packed and adjusted individually until the frame ran perfectly plumb and flat in both directions. The sole plate was shimmed off the concrete floor at the low points and fixed through at consistent intervals to create a level datum for the entire frame. Additional timber noggings were cut and fixed between the ceiling joists at mid-span to give the ceiling boards a fixing point at 600mm centres regardless of joist direction. This approach added time to the first-fix stage but meant all plasterboard surfaces were true and consistent before any skim coat was applied.

The completed room, visible in the final photograph, shows a fully transformed space. All four walls are smoothly skimmed and painted white, with flat surfaces free from undulation or joint lines. The ceiling carries an equally smooth skim coat and has been fitted with a multi-head track light fitting. The window is fully revealed with neat plastered returns, and new skirting boards run around the room perimeter. The before-and-after collage in the final image makes clear the scale of the transformation — from a congested brick garage used for storage to a clean, dry, plastered room ready for use as a home office or additional living space.

The homeowner in Barnet now has a fully usable additional room where previously a cluttered garage stood. The walls and ceiling received a complete two-coat skim and the room has been decorated and furnished as a home office. The conversion adds functional floor space to the property without requiring planning permission and adds measurable value to the home. The plastering stage was completed over four days, covering the full boarding, taping, and two-coat skim across all surfaces, and the room was ready for painting within a week of the work starting.

Garage conversions involve multiple trades working in sequence, and plastering is the trade that determines the final visual quality of every finished surface. Boarding a garage conversion correctly requires the stud frame to be built absolutely plumb and true before any boards go up — if that foundation is wrong, no amount of skimming can correct it. Equally, skimming directly onto new plasterboard without the correct PVA preparation risks the plaster drying too fast and cracking. With over ten years of experience plastering garage conversions across Barnet and North London, London Plastering Service understands how to sequence each stage correctly so the finished surfaces are ready for decorating without remedial work.