Im repairing a bedroom ceiling that had some water damage from rain water. Ive just had a new roof installed so the water source is taken care of. After scraping all loose paint, I am puzzled as to what my ceiling is made of and the best route to take to repair it. Here are some pics. What is that hole?

My home was built in 1959 and in Chicago, IL
Thank you.

 

That's plaster. The base coat is the cement looking stuff that went on first, the finish plaster goes over it and is what get's painted.

I'm not well versed in plaster so I'd repair it with a setting compound like durabond. It does a decent job and is more diy friendly than plaster. Our plaster pro should be along later with better advice for you

 

What you have is a lime based finish (probably whitecoat which is lime and gauging plaster. The lime gives it workability and volume, the gauging makes it set.) This is applied over gypsum plaster and given the age of the house it is probably applied over gypsum lath. RockLath is or was USG's brand name.

It looks like there is still some loose finish. Scrape off all that is loose before you try to fix it. If the base coat (called the brown coat) is still good and hard and not crumbly or chalky you can finish with joint compound. I like EasySand by USG. There are other brands. The number on the lable -- 5, 20 45 or 90 -- is the set time of the material in minutes. Mix as much as you think you can apply in the given time. Smooth it out and try not to overlap the old work. Just work to the old work so you end up flush.

The hole could be a couple of things. It might have been made to drain the area above when the roof leaked. It might be where the water dripped and eroded the plaster. Maybe it is left from a toggle anchor. Maybe there was a nail that missed the stud and when it got wet it rusted and left the hole. Dig out any plaster around the hole that is soft or crumbly or chalky and fill it with some setting joint compound. If it does not get any bigger than it is now it will fill when you do the rest of your patching. If it gets bigger you will need to install something for the mud to stick to or hang on. Let us know what you find and then we can tell you more.

 

The era in which your house was built was a period when plaster and plasterers were the best in Chicago. I think if the brown coat is sound and if you decide to fix this with setting joint compound that you will get along better if you primw the brown coat before you apply the material. It should lay down a little better for you. While joint compound is more amateur friendly than plaster it does not have quite as much body. It might take multiple coats to get it built up to flush with the surrounding existing. As soon as one coat sets you can apply another coat, that is if you use setting mud. If you opt for regular mud each coat will have to dry.

 

Thank you for your expert advice! I was a little scared to keep chipping away at the white layer but removed removed all the loose white layer.

I am very lucky this house was built by those expert plasterers in 1959, because my roof leaked for about 2 years (I had to save the funds for the new roof, i tried putting plastic containers in the attic to catch the rain, but they would overflow) I believe the ceiling would have gave way, if it was built with anything else.

Thanks again! I've already applied one layer of joint compound, just waiting it out for it to dry.