Replacing polystyrene coving

[simon w]

Before Wednesday of this week we had nasty, old polystyrene ceiling tiles and matching coving in both our bedrooms. The titles and coving have been pulled down and the ceiling has been skimmed by a plaster.

So, now I have to put up some new coving... I've searched around a bit, however your input/guidance would be appreciated.

I'm planning to follow this guide and use polystyrene coving because:
Lightweight (I'll be doing it on my own)
Easy to cut
Flexible so it shouldn't crack when/if the walls and ceiling move
It will mould to any unevenness on the walls

Some questions:
1) Once painted, will polystyrene coving look like polystyrene (i.e. a bit nasty/tacky) ? A clean, smooth finish is what I'm after. If polystyrene can't provide this, is there an alternative that's easy to use and available in high-street DIY shops (B&Q, Wikes, etc)

2) I bet these walls aren't true, so two 45 degree cuts won't line up perfectly. Should I a) cut two 45 degree angle and fill any gaps later or b) attempt to cut odd angles so they match perfectly?

3) Does it matter where I start/finish in the room? The master bedroom has internal and external corners.

4) On straights, should I butt pieces together or mitre them?

Edit:

5) On this page what measure does 127mm refer to, a or b?

[code:1]
a.
__________
| /
| /
| / b.
| /
|/
[/code:1]

 

[Third_Eye]

Polystyrene coving can crack also. It can crack at joints and above & below it. Even when painted with matt emulsions, as the flexibility of the polystyrene coving can make matt emulsion crack.

You are best using Gyproc Coving as it it is more hardwearing. Also it is flexible but not as much as polystyrene coving.

Gyproc Coving "can" be applied to uneven cieling and walls. Though the gap can slightly increase and/or decrease. Leaving a thicker edge in certain areas.

In these circumstances what painters do is they emulsion just the face of the coving a colour and use a different colour on walls and/or cielings. This process disguises the thicker edge caused by uneven walls and cielings.

However, there is flexible solid polystyrene coving out there which is specifically made for uneven walls and cielings.

(ps How did you get to highlight that word "this" and have an url in it ?)

 

[JohnD]

He did it like this

[url=http://www.british-gypsum.com/pdf/lit_cove%20cornice%20booklet_feb05.pdf]this[/url]

(But how did I do that?)