Monday, June 11, 2012

Do over

Well, I woke up this morning not feeling good about the plaster medallion we put up yesterday. After we got the last of the four outer ring sections on Megan pointed out that the last one we put on wasn't really sitting right. I looked at it and with an authoritative air to my voice said something like, “Oh, it's just not made that well. We'll clean that up when we fill in the gaps with plaster.” I think more than anything I just wanted to be done for the day and didn't really care.

It bothered me all night and this morning as soon as I was dressed I was up on the scaffolding looking to see how bad it really was. I was bad. In fact, both of the last 2 sections we put on were not sitting properly and both in the same way. They both were high on one end, and it was the end that was furthest away from the last screw.

That was the first problem I noticed.

I thought about it at work all day and made the management decision to remove at least that last one we put on to see if I could fix it. My fear was that the plaster had set up to a point that I would do more harm than good trying to get it off. Well, fear not, the plaster wasn't doing shit to hold anything on. The plaster we mixed up to secure the ring sections to both the main body of the medallion and the ceiling set up so quickly it never adhered to anything else but the ring piece itself. As soon as I took the screws out the piece fell in to my hand.

So there were two problems. First, the screws should have been towards the inside of the ring so if one side sat proud it would be the outer side which could be filled with plaster against the ceiling. Second, don't use plaster to put these up. Or at least don't apply it to the medallion first. The Plaster of Paris the medallion is made of just sucks all of the moisture out of the newly mixed plaster and it becomes useless to secure the parts to anything.

I think maybe if we had applied the plaster to the ceiling and then stuck the medallion sections up it would have worked. (I wonder if that is what I did in the dining room? I should take notes.) In fact, when they put up the original medallions, they first cut holes in the ceiling to expose the lath and then applied the medallions to the ceiling so they had their own keys in the lath. I did that with the one in the stair hall. Because it was so massive, I wanted the extra security.

So after the first ring section came off so easily I took the other four off. There was no evidence that the plaster we applied before putting them up was doing anything to hold any of them in place. The problem now was that I had globs of hardened chunks of plaster stuck to the bottom of them. I took them out to the shop and used an RO sander with 80 grit to grind off the plaster. It was an incredible mess. By the time I got through the forth one there were white clouds of plaster dust billowing out of the shop door. I'm not kidding, it looked as if the building was on fire. The worst part was I had to do the same thing to the edges of the main body of the medallion, so the parlors are off limits until the dust settles. It wasn't nearly as bad as what happened in the shop because there was much less plaster, but it was bad enough that I don't want to be in there.

So tomorrow I'm going to put the ring sections back on, only this time I will use screws and construction adhesive. Most importantly I will put the screws towards the inside of the ring so that if the piece does not sit flush it will at least be flush where it joins to the main body of the medallion and I can fill with plaster on the outer edge. I think Megan is coming by tomorrow, which would be nice because a second pair of hands will be helpful.


mickmaguire said...

a bit late for this I know, but... to stop the dry plaster sucking up so much water and compromising the bond, plasterers will often use a watered down PVA (wood glue works fine) - mix some into water and spray on - the day before, it will reduce the porosity, but not kill it.

There is a product in the UK specifically for this kind of use called unibond - its usually needed for applying plaster or cement stucco to old dry brick - I dont know if you can get it in the US.

Greg said...

I use a product called Weld-Crete, commonly referred to around here as "the blue stuff", and did use it in the room. I only use it on old plaster before applying the skim, though, and never considered using it on new plaster. That probably would have done the job of keeping the medallion from sucking up the moisture.