How to plaster a square edge?

Question

Hi all,

I currently have cornice in a room that will be replaced with a square edge, and I have some questions about the process.

Being a 1970s home, the wall and the ceiling gyprock has quite a large gap from the Junction. I plan to cut out gyprock strips and insert them right up onto the ceiling joist from the wall to bridge that gap.

If the gap in the ceiling is large, I will do the same with the thicker ceiling gyprock as well.

I plan to use a wide, hybrid corner tape.

However, I wanted to ask this forum if I should be utilising an angle bracket, and if so, how? I could put an angle on the EXTERIOR of the corner. I could also use a pvc internal corner bracket instead of tape. I note intex has a angle/tape product, but it isn't listed in bunnings special order despite carrying the brand

I considered shadow line but I don't think the wall is straight enough and my plaster skills aren't quite there.

Thanks!

JacobZ · Answer

Hi @Doladin,

You're absolutely going to want to use an angle trim with the holes in it like the one you've linked to.

The holes are there so the plaster can mechanically lock onto the trim. When plaster is applied, it pushes through the holes and hardens on both sides of the metal. This creates a strong physical bond that holds the trim firmly in place instead of relying only on adhesion to the metal surface.

I can imagine it would be easier than altering the wardrobe, but if you'd like to go down that route, I'd still be happy to assist however I can.

Jacob

Doladin · Answer

Hi @JacobZ

Appreciate the quick response!

Would you recommend a solid angle, or a cross drilled (for lack of a better term) like the one below?

https://www.bunnings.com.au/siniat-30-x-2400mm-90-internal-angle-plaster-trim_p0730709

My walls absolutely won't be square, or I'd have a crack with just tape. I'm doing all this as I ordered a wardrobe that was too tall, after pulling out the useless built in one. Plastering the room to square edge seems easier than cutting the wardrobe down and linking up the cornice!

JacobZ · Answer

Hi @Doladin,

Thank you for your question about square setting your ceiling to wall junctions.

You might like to start by having a look at Gyprock | The Red Book - Residential and Commercial Systems, particularly Book 2, which is the residential installation guide. On page 93, you will see information on how to square set internal corners.

This shows a vertical join, but the principles are the same with a ceiling to wall junction.

Standard Gyprock CSR 75m Plasterboard Perforated Paper Jointing Tape has a line down the centre of it that indicates the centre of the tape so it can be folded for use in corners. This is what is typically used for square setting internal corners.

There are also options like the Strait-Flex Tuff-Tape or Strait-Flex Uno-Bead which are likely similar to what you saw on Intex's website.

There are also Internal Angle Plaster Trims which are attached to the plasterboard using an adhesive like this Intex MegaGrip Corner Bead Spray Adhesive or with staples. The adhesive and staples offer support prior to the application of your plaster, which will greatly strengthen the connection once dry.

In my experience, having worked closely with plasterers during my time in commercial construction, a metal trim is easier to work with when you can't guarantee the wall and ceiling are at a perfect 90 degrees because the nib on the inside of the trim will always be 90 degrees if it is not bent during installation. It is much easier to get a nice clean line because a metal trim is rigid, whereas tapes are not. For this reason, I'd encourage you to consider using a metal trim like the one I mentioned above.

After installing your trim with adhesive or staples, or a combination of the two, you would apply a two-coat jointing system, with first coat being a base coat such as Gyprock CSR Base Coat 45 which gives the join strength, followed by a wider coat of a topping compound such as Gyprock CSR Less Mess Topping Compound which is smoother and much easier to sand.

After the compounds have fully dried, sand them with a plaster sander or sanding sponge, brush down the walls to remove all plaster dust, then prime and paint.

Let me know what you think and if you have any further questions, please don't hesitate to ask, I am more than happy to help.

Jacob