Nice clean cut in cornice???

Kitchen is progressing well (not according to SWMBO) but I have encountered a problem with the range hood.
The hood is attached to the wall and the flex vent goes through the wall, there is a SS guard that goes up to the ceiling (purely decorative) and I need to place some nice clean cuts in the cornice at the top to finish of.
The walls and cornice are the old horsehair type material and even a sharp chisel merely compresses everything and a clean cut seems impossible.
Any ideas for what I can use to achieve a clean straight cut?
A jigsaw had problems getting started and seems to butcher everything in it's path.
Piccy below may help.

It's pretty hard to get a clean cut edge on that stuff. In fact I'd stick my neck out and say it can't be done. You're faced with two alternatives:

1. Hack it away, put in your bit of false flue, and plaster up to it.
2. Hack it away, put in your bit of false flue, and scribe a trim around it.

I'd go for option 2 because I reckon the join will open up over time.

Unless someone has a magic way of cutting horsehair plaster.

How about trying a 4" angle grinder with a masonary cutting disk in it. As there are no teeth to catch in the fibres it should just burn through them.

You could try it in the centre of the area first to see if it would work.

yup - angle grinder or dremel - alternately, would it be easier and more do-able to cut the metal cowl?

Thanks for the responses, may try the dangle grinder and a bit of trim later.
The dremel is too small for such a large cornice, I had tried that before but thanks anyway.
Oh well, more white dust tomorrow, SWMBO will be pleased, a chance to try her new vacuum cleaner :D
Metal cowl is not an option, my metalworking skills are far from brilliant.

There is an angle grinder blade that they use on stainless steel that is half the thickness of a normal blade. I use these to slice through odd jobs that they are not designed for without burning with relative ease.
Jack ;)

dont use the vacuum too much on the plaster dust, it absorbs the moisture and clogs up the workings and rusts everything,
A lesson we learnt on our new vac!!!

we use the old one for the renovations and the new one for the house (needless to say the new one is hardly used!)


GAz

witt is the lowest form of humour, (that dont sound right!)

Sarcasm is the lowest form of wit?
Thanks for the advice on the vac, she uses a brush and pan for such jobs.
Great working arrangement, I mess up, SWMBO cleans up............coming dear :rolleyes: