Square Edge Plasterboard

What Is Square Edge Plasterboard?

Square-edge (SE) plasterboard is a gypsum core panel faced on both sides with paper, whose long edges are cut perfectly straight rather than tapered or bevelled. 

When two boards meet they form a “butt joint” that sits flush with the surface of the sheet.

Applications

• Traditional Plaster Skimming: This is its most common and ideal application. Square edge boards provide a perfect, flat substrate for applying a full 2-3mm skim coat of gypsum finishing plaster across the entire wall or ceiling surface, resulting in a classic, hard, and smooth plaster finish.
• Behind Decorative Battens/Strapping: Often used when a decorative finish involves timber battens, panelling, or strapping that will cover the joints, eliminating the need for taping and jointing.
• Concealed Areas: Suitable for areas that will not be seen or directly decorated, such as within lofts, behind fitted furniture, or in service voids, where a seamless joint finish is not a priority.
• Tiling Substrate: Can be used as a substrate for tiling in dry areas where a full, rigid, flat surface is needed. (Note: Moisture-resistant square edge plasterboard should be used in damp areas).
• Encasing Structural Elements: Employed to box in structural beams, columns, or pipework, particularly when the intention is to fully plaster these elements or clad them with another material that will conceal the board joints.

Benefits

• Ideal for Skim Plastering: Its uniform thickness across the entire board provides a consistent base for the application of a full skim coat of traditional plaster. 
• Uniform Surface for Full Covering: When the entire surface is to be covered by another material (e.g., large format tiles, timber cladding, or decorative panels), the flat, non-tapered edges ensure a consistent substrate, simplifying the installation of the overlying material.
• Concealed Joints: Particularly useful in applications where joints will not be taped and filled, but rather hidden by architectural features such as battens, decorative strapping, beadings, or even where the entire wall will be wallpapered with a robust paper.
• Structural Versatility: Provides a strong and stable lining for internal partition walls, ceilings, and encasements. Its rigidity contributes to the overall stability of the framed structure it is attached to.
• Cost-Effective Base: As a standard plasterboard type, it offers an economical solution when the intention is to apply a full plaster finish or to cover the joints by other means.
• Variety in Performance: Like tapered edge boards, square edge variants are available in different performance types (e.g., fire-resistant, moisture-resistant, acoustic, impact-resistant), allowing for specialised applications while retaining the square edge profile.

Finishing Methods

Two-coat skim (traditional method)

• Bed 100 mm scrim tape over every butt joint and external corner.
• Apply a tight coat of gypsum finish plaster, key it, allow to firm.
• Lay a second thin coat, trowel flat and polish.

Direct decoration
If the substrate tolerance allows, joints can be filled with a setting compound, sanded, and the board sealed with a proprietary drywall primer before painting. This approach is common on small utility rooms or temporary partitions but requires meticulous joint filling to hide butt joints.

Key difference from tapered-edge: SE boards must be plastered or fully filled and sanded; they cannot accept a simple tape-and-joint finish without feathering because the joint sits proud rather than recessed.