coving!

Try to avoid but joins, internal corners are easy to deal with

Plasterboard ceiling on block wall is pretty standard so I don't see a problem left uncovered.

Our house has a timber fillet in the wall ceiling angle instead of coving, which gives a lighter less heavy effect. Just a strip of 1.5 x 0.25 inch wood, like a mini skirting board at the top of the wall.

Ed

Thanks. Yes, considered scrim, and will use it, but wondered if there was anything else. Mackers, I'll have a look for your suggestion.

For external angles I use expanded metal lathe and jointing compound. On an internal angle when PB meets that is mounted on dissimilar surfaces I don't like to scrim. I am sure it does work sometimes but it depends on so many factors.

For sure when I mount PB on my solid stone walls and it meets PB on my suspended ceiling (on metal galv studwork) I prefer to finish sharply at the corner using jointing compound if required because there is a feathered edge - neatly scrape away any excess when nearly set - I even try to make a groove. Then fill with a bead of white acrylic 'silicone' (ie not silicone!) - fingered or spread with a silicone tool (can i use fingered and tool in the same sentence!). I use one that has a textured finish and by the time I have rollered on the paint you can't see it. Fill any large gaps with jointing compound first. No cracks so far.

I've done a few of these - have used fibreglass drywall tape and a 90degree trowel, or just done it with a regular trowel. Then fill the corner with a bit of painter's caulk (acrylic, not silicone). This gives a more even edge and makes it easier to get a nice clean "cut" for painting. I've also used paper-faced steel internal angles for this purpose. These are very strong and will not crack - still fill the corner with painter's caulk, though, just to make a clean line. If you don't use anything, you will always get a crack. I find the fibreglass tape a bit easier to work with than the paper drywall tape - but both work OK. At least the fibreglass tape you can stick in place first - makes it easier for wall-to-ceiling joints. The metal angles work OK for this too, but are a tad trickier to get into place.

Paul in Montreal

p.s. either plaster or jointing compound works for this, but I usually use jointing compound for the final coat as it's easier to sand

This is the inside corner bead: http://www.homedepot.ca/product/sheetrock-paper-faced-metal-inside-corner-bead-b2-3-8-in-x-3-8-in-90-degree/911282

And, for completeness, outside corner bead: http://www.homedepot.ca/product/sheetrock-paper-faced-metal-outside-corner-bead-b1w-9-16-in-x-13-16-in-unev/911279

Paul in Montreal.