Large hole in plaster wall

The house was built in 1939. It has 18" thick stone walls, finished on the inside with plaster. There is no lath, it is a material that kind of looks like drywall with holes in it for the plaster to hold onto.
A roof leak (fixed) left a wall with a large hole. (6 feet by about 2 feet)
What would be the best way to fix this? The water did come down between studs, so there is good wood on either side of the hole. Is that board with the holes a good approach? I have done a lot of home repair and remodelling stuff but never had to fool with the walls before.
Any ideas are appreciated.
Mac
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http://www.oldhouseweb.net/stories/Detailed/202.shtml
If you have no experience with plaster, it may be easier to rework the area with gyp board. Square up the hole. Buy and install one or more layers of drywall to match or stay slightly below the wall plane. Build up, blend, sand, etc there are many sources for information about drywalling.
If your really want to try plastering, find a source for Structo Lite in your area. Here is some information: http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=structo+lite It is a perlited USG product that you can use by just adding water. Gives a good product without having to blend multiple materials.
Depending on the finish on the original plaster, you may be ahead to contact a plasterer.
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William McHarg wrote:

Les
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The 18 inch thick stone wall may make that difficult. :)
Mac
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