How To Cut plasterboard

Plasterboard is made up of heavy paper lining filled with a gypsum core. To cut plasterboard you only need to cut through the face of the plasterboard board sheet with a sharp trimming knife blade. Snap the plasterboard along the cut in the face. Then cut the paper lining from the back of the plasterboard sheet.

The job is made easier with a plasterboard tee square. These can be bought for a small cost from any plasterboard retailer. Tee squares come in 1200 mm and 1350 mm widths.

Plasterboard is easier to cut if it is standing up rather than laying on the floor, as you can walk behind the plasterboard sheet to cut through the liner.

If your plasterboard sheets are stacked flat, cut the face of the plasterboard sheet then raise slightly the plasterboard sheet where you made the cut. Now you can make cut through the back liner from the face of the plasterboard sheet. Only cut from the center for about 600mm then lay the plasterboard sheet back down, go to the end of the sheet and pick the shortest end up about 300 mm, holding both sides give the sheet a flick and you will get a clean break without delaminating the liner. With a bit of practice, this method can also be done with the plasterboard sheet standing up but when you flick it back the sheet needs to be upright, not leaning back.

Making a horizontal cut along a plasterboard sheet is the same cut and snap method as described above, but can be difficult if you are on your own. To make this easier, after you snap the plasterboard sheet don't start cutting the back from the end, start about 600 mm from the end. This will stop the strip from falling away and breaking. Cut all the way along stopping 600 mm from the other end, go to the center of the sheet, then with a sharp snap back toward you, the plasterboard strip will break cleanly allowing you to have control, preventing the plasterboard strip from breaking.

Cut outs for doorways are easier, nail the plasterboard sheet over the doorway before cutting out the door opening. This will prevent you from breaking the plasterboard sheet while lifting it into position. To cut out the doorway, use an old saw, using the door stud as a guide cut up both sides until you reach the door head. Then using the door head as a guide cut the back of the plasterboard sheet, fold the it outwards then cut the face along the crease.

Cut outs for windows are different as you can't go behind to cut back of the plasterboard sheet. You have 2 options, either cut the opening out before fixing the sheet, or fix the sheet over the window then cut out the opening.

  • Option 1. Cutting out the opening prior to fixing the plasterboard sheet, can result in breaking the plasterboard while lifting into place. Here are some tips is you use this option. Fix the plasterboard sheets to the window wall before the other 2 sides to allow you to cut the plasterboard sheet a little short to avoid jamming, resulting in the plasterboard breaking. Measure the vertical cuts from the same end, allow about 5 to 10 mm clearance. With the sheet standing up, ready to position, mark the vertical cuts with a pencil, then mark the horizontal cut with a chalk line or pencil. Make the vertical cuts using a saw and the horizontal cut using the trimming knife, carefully snapping the sheet. The sheet will fit into place comfortably without jamming up.
  • Option 2. Cutting the window opening after fixing the plasterboard sheet is perhaps the safest option to avoid breaking the sheet. Cut the plasterboard sheet to length and fix in position by nailing the corner studs and along the bottom or top plate only. Mark the horizontal cut using a chalk line or pencil, cut the vertical cuts with a saw using the widow frame as a guide. Once you have made the vertical cuts nail the sheet along the join before making the horizontal cut. Cut along the horizontal line on the face of the sheet, push the off cut in towards the window this will allow you to cut the back liner from the front of the sheet. You don't need to cut the entire length as you can gently fold the off cut back towards you and it will snap cleanly providing you have cut 50% of the back liner and the back liner is cut up to the vertical cuts. If you have difficulty making the horizontal cut this way, (IT CAN BE TRICKY), an alternative is to mark and cut ONLY the horizontal cut on the back of the sheet prior to fixing. Then when you make the face cut it will just snap off very easy, providing the cuts are made at the same height.

General tips on how the hang or fix plasterboard sheets

Tips on how to fix or hang plasterboard sheets to walls

Tips on how to fix or hang plasterboard sheets to ceilings

General tips on troweling or stopping up plasterboard joins


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