Instructions

Many people simply remove wallpaper, apply a thin layer of plaster to the wall (this is known as skim coating) and then re-paint the wall. Often the wall cracks and the surface is compromised within a short time. To help prevent this we recommend that old linings be removed and new plasterboard is used.

There are many good reasons for doing this:

• The hassle of stripping wallpaper is eliminated.
• Insulation can be installed in the exterior walls - houses built before 1979 were not required to have wall insulation installed.
• New electrical sockets can be installed and old wiring replaced.
• New plasterboard is easy to stop and will give a much better finish.

All tools should be clean and free of any old and set plaster. It is recommended that stainless steel tools be purchased if possible as these are less likely to corrode. Remember that these tools are being used to create a smooth finish, any kinks or scratches in the edge of the tool will cause rough areas in the plaster. Do not use broad knives for scraping, opening paint cans, etc.

Paper Tape

Paper jointing tape offers superior crack resistance and is the only jointing tape recommended by most plasterboard and joint compound manufacturers. It achieves this because the paper tape absorbs compound, melding with it to form a solid joint. Non absorbent fibrous tapes are unable to do this. Paper tape comes pre-creased and has two distinct sides. The rougher side, facing out on the roll, is always bedded face down into the compound.

Joint Compound

Below is a summary of the compounds suitable for use by DIYer’s when jointing plasterboard.

At external corners, and for holes or gaps deeper than 3mm, the plaster is applied in thicker coats. Because of this, pre-mixed compounds are only recommended for the final coat in these situations. Below is a summary of the compounds suitable for use in these instances.

It is recommended that joint compounds from the same manufacturer as the plasterboard be used. In this way you can ensure that the materials are compatible and have been tested as a system.

Stopping The Plasterboard

Edge (Longitudinal) Joints

These are the joins where two edges of plasterboard meet side by side. The plasterboard will have a slight recess (taper) in the edge of the plasterboard, making for easier stopping.

Preparation

Ensure that all fixings, screws or nails are seated below the surface of the plasterboard. Fill any areas greater than 2mm deep with a setting compound such as Gib Tradeset® and leave to dry. Remove any dust or loose material from the plasterboard. Mixing instructions can be found on the back of the bag or pail.

First Coat

• Using a 150mm broad knife, fill the recess formed by the edges of the sheets with jointing compound.
• Centre the paper tape along the joint and using a 150mm broad knife press the tape down into the compound.
• Draw the broad knife, held at approximately 45 degrees, to the board surface along the joint to remove any trapped air bubbles beneath the tape. Ensure that sufficient compound is left behind the tape to achieve a good bond.
• Immediately apply a thin coat of compound over the surface of the tape. This reduces the possibility of the tape curling and wrinkling which can lead to edge cracking.
• When the compound is set (or dried) scrape back any build up of compound along the joint.

Second Coat

• Apply a second coat of jointing compound with a 200mm trowel. Ensure that this coat extends outside the area of the first coat.
• Feather the joints to eliminate build up of the compound at the edges.
• Allow to thoroughly dry (24 hours) and scrape back any build up of compound along the joint.

Top Coat

• Apply a finishing coat of compound with a 280mm trowel. Joint edges should be feathered at least 50mm beyond the edges of the previous coat.
• Allow to dry for approximately 24 hours.
• Lightly sand in the same direction as the joint using 220 grit, or finer, sandpaper.
• After sanding, mark any defects and imperfections with a pencil, then retouch these areas with compound. Leave to dry and sand. Repeat this process until the desired finish is achieved.

End Joints & Cuts

When jointing sheet ends which are not recessed, care needs to be taken to ensure the surface build up of compound is minimised. The same basic procedure as for tapered edges should be followed, except that each of the stages should be doubled in width, resulting in a 600mm finished joint width.

Nail & Screw Spotting

The same process and compounds should be used as for stopping longitudinal joints.

• Use a 100mm broad knife for each of the first two coats of compound. 
• Leave first two coats to dry for 24 hours prior to applying the finishing coat. 
• Use a 150mm broad knife for the finishing coat. 
• Leave to dry for 24 hours and then lightly sand with 220 grit sandpaper.

Dealing With Corners

Internal Corners

1. Using a 75mm chamfered broad knife, apply the compound to both sides of the corner.
   TIP: Keep the high side of the chamfered broad knife toward the corner, this helps reduce removing compound from the other side of the corner during application. 
2. Measure and cut the paper tape to length. Fold the tape along the centre line (crease) and bed the paper tape into the compound using the 75mm chamfered broad knife.
3. Apply a thin coat of compound over the top.
   TIP: Apply the compound to one side of the corner at a time and leave to set/dry in between. This way the compound is hard on the opposite side of the corner and the compound will not be scraped off.
4. Apply the final coat of compound, ensuring that the edges of the previous coat are completely covered.
   TIP: A special corner tool can be used to do this or a 150mm broad knife can be used following the procedure of doing one side at a time.
5. Leave to dry and lightly sand with 220 grit (or finer) sandpaper. Sand in the direction of the joint, being careful not to scuff the paper.

External Corners

External corners can be finished with metal trims or Gib® Goldline® profiled plasterboard trims. Gib® Goldline® trims are available in a range of different profiles including rounded corners that are great in high impact areas. Trims are attached over the corner and then covered with compound. Because of the thickness of plaster involved in covering these trims, pre-mixed compounds must not be used for the first two coats. Use the compound selector in Table 2 when selecting compounds for this application.

1. Nail or screw the Slim Angle to the corner. Fix at 100mm centres on alternate sides of the corner (fixings should also be placed on both sides at each end of the trim).
   TIP: Gib® Goldline® trims should not be nailed. These are held in place by first applying a coat of compound and embedding the trim into the first coat of compound. Once dry they are finished in the normal manner. For more information contact Gib® Project Support on 0800 442 4663. 
2. Using a 150mm broad knife or 200mm trowel, apply a first coat of setting compound. 
3. When hard, lightly scrape back using a broad knife or the edge of a trowel.
4. Apply a second coat of setting compound using a 200mm trowel. When hard, lightly scrape back.
5. Apply a third coat of pre-mixed compound using a 300mm trowel and leave to dry.
6. When thoroughly dry, lightly sand in the direction of the joint with 220 grit sandpaper, taking care not to scuff surface paper of the plasterboard.

Skim Coating

Skim coating involves covering the entire plasterboard surface with a thin layer of finishing material to give a smooth, consistent texture across both joints and the paper surface of the plasterboard.
If skim coating is the only option for you, or you have a special requirement for a very smooth finish such as in a critical light area, then it is recommended that a tradesman is used. Walls must be prepared in different ways depending on whether it is new plasterboard, has been painted, has had wallpaper or even if the plasterboard is old. A tradesman will be aware of the correct way of preparing the wall to reduce the risk of problems in the future.

Checking The Jointing

The quality of the final decoration is dependent on the quality of the jointing. Using Table 4, inspect the quality of the jointing prior to decoration. TIP: Imperfections will be easier to see by shining a light, such as a torch, along the wall. This will show up any imperfections as shadows.

Decoration

Paint

There is plenty of information available on painting plasterboard, however, the following guidelines give a summary of best practises.

Use flat paints rather than semi-gloss or gloss where possible. Gloss paints will reflect light to varying degrees, exaggerating surface imperfections.

Light colours tend to diffuse light helping to disguise any surface imperfections. If it is intended that dark colours will be used then it is recommended that the services of an experienced tradesman be sought.

Avoid the use of harsh lighting such as wall washers or creating situations that give harsh light, such as windows extending to a wall or ceiling line. Where ‘harsh’ or ‘critical’ lighting conditions occur, i.e. where the dominant light sourceshines across the surface, imperfections will be easily seen. Consider skim coating the wall or applying a wallboard prep coat. Use water-based paints, except in wet areas, as these will make it easy to create an ‘orange peel’ effect which helps to disguise any imperfections.

‘Cut in’ around edges and doors with a paint brush and then apply the remainder of the paint system using a medium to long nap roller (7-20mm). This will aid in creating a soft ‘orange peel’ effect. Always maintain a ‘wet edge’ with the roller and apply the last coat with the roller marks in the same directions and parallel to the dominant light source.

Paint systems should always be applied in accordance with the manufacturer instructions.

Wallpaper

It is important that an oil-based sealer is applied to the surface prior to wallpapering. Some wallpapers are quite thin and the joint may “telegraph through” due to differences in porosity between the joint and the plasterboard surface. Applying a sealer also aids in the removal of the wallpaper at a later date if redecoration is required.

NOTE: Whilst the advice and recommendations contained in this brochure have been produced with proper care, they are offered only with the object of assisting those interested in or involved with the jointing of plasterboard. Winstone Wallboards Ltd and BRANZ do not accept responsibility for the advice, recommendations, etc., contained herein.