Basic Tapes Available
There are different tapes with different function for different areas of the wall. Below lists the different types of tape as well as their function.
1. Self adhesive fibre glass tape for recessed plasterboard wall joins
2. Paper tape for plasterboard ceiling/wall joins, butt joins, internal angles
Apart from being the strongest plasterers tape, it is also the most difficult to use for the casual DIY. The main difficulties experienced are bubbles showing up after painting or tape showing through the plasterboard join requiring the join to be over filled to hide the tape.
Bubbles forming under the tape is caused by either no base coat under the tape or the base coat has not been applied consistently and has dried out in parts before the tape has been embedded.
To avoid this, your mix needs to be a bit “wet” (not runny). Make sure you fill the plasterboard recessed join with base coat ensure no plasterboard or dry spots appear before applying tape. Bed the tape into the plasterboard recessed join using a 5″ or 6″ joint knife.
To avoid the tape showing through, first make sure there are no bumps in the plasterboard. If so, cut them out with a trimming knife. If cutting out the bump creates a large gap, pre-fill the gap and scrap back level before taping. Bed the tape tightly and evenly into the recess, use quite a lot of pressure to squeeze out base coat from under the tape. Use the mix squeezed out to apply over the tape. It is important that the back of the tape is “wet” with plaster. Try short sections at a time until you get used to it. Paper tape stretches, so once the tape is embedded, to finish coating over, start from the center and work to each end. Finally run through the entire plasterboard join from end to end to smooth out any excess. Remember to scrape back the join after the base coat has set, before applying second coat.
Plasterboard butt joints have the added difficulty of not being recessed, so whatever tape and base coat applied is going to sit proud of the surrounding surface. To make a butt joint hidden requires a slightly different technique.
Start the same way as with a plasterboard recessed join but make sure you squeeze out all excess plaster from under the tape. The back of the tape should be “wet” with plaster but don\’t try to cover the tape. Using an 8″ joint knife, fill out each side of the tape, (without applying any more base coat over the tape itself), the edge of the tape sets the level. Use the full width of the joint knife. By using this method you are reducing the build up over the tape and spreading out the join level either side.
Internal corners are best taped in after the plasterboard wall joins. Pre-fill and scape back any gaps over 5mm. As with all paper tape applications it is important to have a continuous “wet” layer of base coat before applying tape.
The easiest way to tape in an internal is to use an internal taping tool. The trap using this tool is, not setting the angle of the tool correctly; or not applying enough pressure to squeeze out all the base coat from under the tape. Make sure the back of the tape is “wet” with plaster and feather out the edges.
Using a 3″ or 4″ joint knife is another method of taping in an internal. The same principles as above apply, however getting a square corner can be difficult. In most internal corners the board on one side will be in behind the gap created by the corner. To get a square finish, on your final sweep with the joint knife, angle the joint knife into the sheet that is in behind the gap. This prevents digging out the plaster that is filling the gap. Use long smooth strokes for the best result.
3. Wet and Stick Paper tape for internal angles
This tape has an adhesive backing similar to that of a postage stamp. The tape is cut to length and run through water to wet the tape. The tape is placed in position and wiped in with a 3″ joint knife. Once dry apply a thin coat of base coat over the tape.
Similar problems can occur using wet and stick as normal paper tape. Unless proper preparation is done these problems can be worse. To prepare the internal for using wet and stick, pre-fill all gaps over 2mm and pre fill all nail holes. Wet and stick tape is also very useful to repair cracked plasterboard joins. It allows you to repair the join with the minimum amount of build up4.
4. Flexi Paper tape for unusual obtuse internal angles
Flexi Paper tape is a stiffened paper tape that can be bent to shape, Used for obtuse internals that a 135 degree metal angle won\’t fit.
Flexi tape will take out minor imperfections in the line of the angle but to get perfect straight angle may still take more work. Flexi tape is used in the same manner as normal paper tape.
To straighten an obtuse angle, hold a chalk line from one end to the other, adjust the position of the line until you “even” up the line, and flick the line to give you a straight line to work to. If you only need to fill a short length, say 300mm to straighten the join, working along the length of the join may be ok, just follow the chalk line. For long runs that may need to be filled out up to 20mm, you will need to work away from the join. The best tool for this is a 12″ joint knife or trowel. This is commonly known as “cross troweling”. Move along the line filling away from the join, working from one side of the join only. This creates a new straight line to work to. Apply a second and top coat working along the join being guided by the chalk line.