How to Finish Plasterboard to Achieve a Professional-Looking Surface
Plasterboard and Drywall sheets are great for quickly constructing and covering interior walls, they make the job quick and are easy to use, cut, and fix.
The only real downside to using plaster board is they need a little bit of finishing to get a smooth clean surface that can be painted.
Any joints, indentations, or holes that have been made by installing and fixing sheets in place need to be filled and smoothed before the plasterboard can be finally decorated, and this process is quite simple and can be handled easily by a DIY newbie, or beginner.
In this guide to finishing plasterboard, we run through the basics and offer handy tips to get a great finish that you will be proud of.
Tools and Materials
There are a few tools and things you will need for the job:
- Jointing tape
- Joint filler
- Jointing cement
- Wide Filling Knife
- Plastering trowel
- Bucket
- Mixing kettle
- Plasters Hawk
- Sponge
- Utility Knife
You can purchase Jointing filler and cement which is pre-mixed in tubs or as a dry powder that needs to be mixed with clean fresh water. If you have a lot of joints to finish buying the powder and mixing yourself will save you quite a bit of money but adds time to the process.
Paper jointing tape is typically 2 ⅛” (53mm) wide, has a crease along the centreline and the edges are feathered to help eliminate any witness lines when applied
Jointing tape is applied over the joints formed by the edges of two sheets of plasterboard and helps to reinforce the joints, preformed or creased tape is available for use on internal corners.
Specially designed Jointing tape, used to reinforce external corners is available, this type of tape has a metal strip running along each side of the central crease to help give the joint strength.
Covering Indentations, Nails or Screws
The first job I tackle when finishing plasterboard is to fill any holes or indentations left by fixing the boards in place, you can find out lots more about how to fit and install plasterboard in our corresponding guide.
Mix up some filler and apply a layer over the holes using a 2” (50mm) filling knife, you need to pick up a small amount on the blade and press it into the holes.
Hold the knife at an angle so that the filler smooths onto the surface but doesn’t damage the board and remove any excess filler, go over the area a few times to work the filler into the hole
Allow the filler to dry off and if required apply a thin layer of jointing cement in the same way. As the cement starts to harden, use a damp sponge to help feather the edges and give a smooth covering.
For more details on how long plaster takes to dry and how to treat it read our in-depth Plastering guide
Filling Tapered Edge joints
The edges of plasterboard are available in two different profiles, square edge and tapered edge, to fill the tapered edge profile, apply a ⅛” (3mm) thick strip of Jointing filler 2 ½” (60mm) wide along the joint, use a wide filling knife and press some jointing tape into the filler and press out air bubbles.
Once the joint tape is flat and evenly set in the filler, a second layer of filler needs to be applied over the tape, this strip should be wider than the tape and spread onto the surface of the plasterboard, filling the taper so that is level with the flat surface of the plasterboard.
Leave the filler to set for a few minutes and then use a damp sponge to blend the edges onto the board surface.
This can be left to set and harden and then checked with a level for any dips, low spots, or hollows, use more filler to level these areas and blend them in with a sponge.
To give the joint a good, strong surface allow the filler to set hard and then apply a thin coat of joint cement, this should be run in a wide band along the joint covering the filled area. I use a wide 10” (250mm) jointing knife for this.
Marshalltown makes great plastering tools, I find them easy to handle and the blades last a long time when looked after.
Once the jointing cement has dried and is fully hardened it can be lightly sanded to knock off any high spots. Then a second, wider band of cement is applied, doing this spreads the joint over a wider area, helping to blend the seams.
Follow the same process as before using a damp sponge to feather and blend the edges, working in circular motions.
Filling Cut Boards or Square Edges
As you fit boards they will need to be cut and they often sit next to factory-made tapered edges, before you apply any jointing tape fill the tapered section to level the surface.
Cut and fit the boards so there is approximately a ⅛” (3mm) gap and press filler between the boards. The aim is to fill the gap and provide a level surface for the jointing tape to sit on
Allow the filler to dry and then apply a thin layer of jointing cement over the filled gap, press jointing tape into the wet cement, and using a wide-bladed joint knife firmly press the tape so that it sits close to the board.
Using a sponge to blend and feather out the edges of the cement, as before, then apply a second wider band of jointing cement over the top and blend this into the plasterboard to remove any witness marks or seams.
Glass Fibre Scrim Tape
As an alternative to paper jointing tape, glass-fiber tape can be used to cover gaps, cover joints, and help to repair patches or holes in plasterboard
Mesh scrim tape is self-adhesive and will stick to a wall quite easily so it doesn’t require the use of filler to bond it to the surface.
Usually sold in 2” (50mm) wide rolls the Scrim mesh tape is cut and pushed onto the surface over the gap, then joint filler is skimmed over the top using a filling knife, this pushes the filler through the mesh and helps to bond it securely over the joint.
Applying Scrim Tape
As with any job, start by making sure the surface you are working on is clean and free from dust, or loose plaster.
Clean up any cut edges using a trimming knife and use the handle of the filling knife to push down any high spots and smooth over the rough edges, trim away any loose paper, using a sharp knife.
Work from the top down and use the filling knife to push the scrim tape against the surface, ensuring it has adhered to the wall gently unroll the tape and press it down over the joint
Ensure the center of the tape is over the center of your joint checking as you work down the wall. The Scrim tape can be lifted up again if you need to adjust the position and get back on the right line, take your time, and don’t pull it too hard as it can come loose.
Roll the tape out until you reach the bottom of the joint or the required length and cut it with a knife, its best to try and cover a joint in one run but when you come to the end of the roll never overlap the tape as this will leave a thicker witness for you to try and hide with filler, and you will be blending it in forever.
Use a butt joint to link two ends together, if you need to make a joint, try to keep the ends as close and flat as possible to avoid a raised edge.
Once you have the joints taped and prepared, mix up some filler in a clean bucket and transfer it onto a flat surface or plasterer hawk, this makes handling it much easier
Use a wide-bladed filling knife and apply the filler over the top of the scrim tape, hold the knife at a gentle angle to the surface and press the filler down, through the mesh tape, and into the joint.
Run the filling knife over the joint to level off the surface and remove any excess filler, the mesh should just be visible below the surface.
Then let the filler dry out and harden, and apply a thin layer of joint cement which is then blended and feathered using a damp sponge just as before, remember to apply a second layer and blend this to give you a good, smooth finish that can then be painted.
Finishing External Corners
For external corners that will be exposed to wear and tear, use a metal reinforced jointing tape to help hold the joint. Cut the tape to the required length and then fold it along the center to help it form around the corner joint
As with a flat, butt joint, apply a band of filler on either side of the boards approximately 2” (50mm) wide on both surfaces, use this layer to hold the folded joint tape in place, working from the top down towards the floor.
Push the tape into the filler using a wide filling knife and remove any excess, so that you remove any air bubble and get the tape as flat as possible.
I try to use square-edged plasterboard for external corners if possible, however, if you only have tapered edge boards fill the tapered section so that it is level and square before applying jointing tape.
Use your filling knife to press the reinforcing strips firmly into the filler and ensure they bed against the plasterboard properly.
Blend in the joint by applying two layers of joint over the tape working up to a 6” (150mm) wide band which is feathered and blended using a damp sponge.
For external corners that are likely to see some action in high traffic areas using a length of either metal or plastic beading will provide added protection and help keep the corner looking sharp.
Read more about plastering and using corner beading in our beginners guide to Plastering
Beading is much thicker than scrim tape and will require a wider band of filler and cement to cover and blend.
In this case, it can be beneficial to use tapered edge boards for the corners, as this will help the beading to sit flush and blend in better.
Finishing Internal Corners
For good results when working with internal corners of dry-lined walls, follow the same steps as for finishing a flat joint, and make sure all the surfaces and edges are prepared and cleaned, just as with an external corner.
First, fill all the gaps with jointing filler, It can help to treat existing surfaces such as ceilings or surrounding plaster with PVA to help and filler bond to the surface, this needs to be a mix of water and PVA and brush onto the surface, check out our post on how to use PVA for plastering
Once the surface is ready, prepare the jointing tape, cut it to length, and fold it along the centerline to help it form into the corner.
Using your filling knife smooth a thin band of joint cement onto both sides of the corner and apply the tape, try to keep it as central to the joint as possible, this is where the refolding will help.
You can buy special plasterer’s trowels for both internal and external corners, however, I like to use a straight edge like a spirit level or length of PSE timber to help pres the paper into the joint, the aim is to squeeze out any air bubbles and smooth the tape against the plasterboard.
Once you are happy the tape is bedding in fully trowel on a strip of cement, around 3” (75mm) wide to both flat surfaces, then use a damp sponge to blend the cement
Once the first layer has dried and hardened repeat the process, applying a second, wider band of cement over the corner and then blending the edges to match the plasterboard surface,
Once the corner has fully dried you can finish the wall by painting or using a wall covering.
For more great DIY tips and ideas check out our blog post and Podcast with information to help everyone improve their home, follow the links below:
This article was written by: Richard Quinton – The DIY Help Desk Owner, Engineer & technical specialist.
Richard is one of the key partners in The DIY Help Desk team. He is a qualified Engineer, writer, and publisher, educated to Master’s level. He is a keen advocate of DIY and home improvements.
Richard enjoys helping others to learn new skills and reach their goals and believes that passing his knowledge and experience on through his writing is an effective way to positively impact the lifestyles and well-being of others on a larger scale.
