Walls and Ceilings - Plaster problems on a fireplace

Here is my problem:

I have plaster over the fireplace that had taken water damage some time ago. the problem for the water had been fixed but not the plaster. i have put drywal compound over and it has held im most places. for some reason there are some areas that bleed something thru the compound and does not hold. I think it may be from what ever was used to smooth the plaster when it was built in the 50s. should i remove the areas that keep giving me trouble or can i seal this with a primer of some sorts and then use compound? I do not think that the water is still leaking but due to just the normal amount of moisture is the compound it has soem type of reaction with the very hard original compound.

In a situation like this I always tell people to go for the cheap, easy fix first. So get some KILZ or some Guard. I don't remember who makes Guard but I understand it's pretty easily available. This is supposed to seal any stains. Try that then prime and paint. If it doesn't work then you can still remove and replace the effected area. It is possible that creosote or other stuff penetrated the brick and plaster. I've seen this happen. If the plaster is sound and bonded the right combination of sealer and primer should solve your problem. After rereading your note something else occurs to me. Maybe you should try some cleaning before you do anything to seal it. TSP, the real stuff not the TSP substitute or a stron ammonia/water solution might be a good idea.

Well, I primed the area that has been giving me problems with killz primer and it did not hold. It stuck to most of the area but the places that were bubbleing it just pealed and fell off as it dried. I think i may have to remove the sections that are giving me problems :(

Try some Bin from zinsser

http://www.zinsser.com/product_detail.asp?ProductID=10

well i have to say the product from Zinnser worked like a charm. I put on one coat and 5 min later a second wet coat and it sealed and dried in 15 min and i was able to mud it up with out the problems ive been having. THANK YOU!!