Originally Posted by mikew
....Will it take mud and then paint as the drywall?
No, it won't. You may be able to get the compound on the product, but it will not stick appropriately, nor will it stay intact. It would crack and fall off.
We have done many jobs similar to to what you are describing, in terms of scribing up to an irregular edge.
(IMHO: I think the "Foam Board" is a bad idea for what you want to achieve)
If you want to make your life easier when doing the contoured sheet-rock cuts in the boards, do this:
Draw your tracing (or scribing) with a pencil of that specific "shape" that you are trying to get the sheet to go against. Review and check your lines.
Then take your utility knife and score that same drawn line.
Last, take a drywall router and cut the line out, going left to right.
No fuss, no effort: clean, simple, smooth.....and FAST....
(The above is how the pros do it)
Preparation: Prior to doing your compound coating phase, you should masking tape/plastic off everthing on the logs that are against the drywall, since you want that compound up close to it.
Compound Coating Work:
You may find it easier to apply the following "mudding" tip for hard to reach areas. After applying any mesh or paper tape to the areas against your contoured edges, coat using smaller sized knives as best you can. When dry, go back and scrape down any ridges that were left. If there are still some "rough" areas, sand them down. Then get a good quality set of paint brushes and mix up the compound to a "yogurt" like consistency.
Use the paint brushes to apply a nice smooth coat of compound over those areas that are closest to the logs. When dry, sand that work smooth using a small drywall sanding sponge.
After completing the drywall phase of your project, remove the maskign tape and any plastic. Use an appropriate latex based caulking to seal up any smaller crevices or areas still left (next to the logs).