Repairing Plaster Crown Moulding Questions

[Mick_VT]

European plasterers often use this product called unibond (well in the UK they do) it is essentially PVA glue - (yeah white wood glue). It is used in a couple of different ways, but one thing they do is mix it into water then paint the old plaster with it, it acts as a sealant that stops a bunch of the wicking effect Texas describes, but not so much that the new plaster cant key to the old. They often mix it into browning coats as well to help with adhesion.

I learned all this when I learned how to plaster with pink plaster back in the UK about 20 or so years ago - I used to be able to get a surface like glass after applying browning and top coat to raw brickwork.... loved it

[kelt65]

It says in the comments section that is what the pink stuff is - the plaster weld. I have never heard of this product before.

(Stays up till 2:30 a.m. watching plastering videos, fascinated.)

AFAIK plaster weld has the same job as the water mentioned in the original post. Plaster (except clay or "mud" plaster) cures chemically and doesn't just dry. For that process it needs water and if the old plaster sucks the water right out of the fresh material the new plaster won't cure and remain soft and powdery forever. Most European preservation plasterers consider plaster weld completely useless and just go with water.

Err, it isn't about moisture at all it's about adhesion more specifically (while moisture plays a big role in adhesion of course there are other issues as well), and making plaster work with other material, like drywall, or layering it over unstable surfaces like latex paint. Plaster weld or weld-crete is used extensively when you want to skim over your walls that have many layers of paint, or want to blend a drywall panel into a plaster wall. When the alternative is stripping the paint off the existing plaster ... plaster weld seems very attractive. I don't know of any other solution to bond plaster to drywall panels. It doesn't matter what you think, sometimes it must be done.

That said it isn't for bonding plaster to plaster at all. Don't see it's point here, but then that guy is the pro, not me.

[Mick_VT]

I should add that my uncle used to own one of the oldest companies in the UK to specialize in fancy decorative plaster work (seriously the company was about 300 years old). They worked on many of the large stately homes in the UK, and he even worked on ceiling repairs at 10 Downing St. The company was so old and well established they often had the original moulds for plasterwork from 18th century mansions in their storeroom, that could be re-used if repairs or restoration was required.

Most of the fine plasterwork was actually made of Plaster of Paris backed by wood strips and sackcloth. When they installed it, they used plaster of Paris for the repairs, as it is extremely fine grain and easy to work.

My advice from my little knowledge on this job would be to stuff newspaper into big holes to provide a backing (if you want to get real fancy use plaster of paris soaked cloth), then use very watered down wood glue as a sealer on the cracks (as detailed above), you dont need to let the glue mix cure just let it dry (20 mins or so), then build up the voids with plaster of paris. Build it high, let it set, then carve and sand to match the surrounding profiles. Tighter cracks should be v'ed out before you start. Larger holes can often benefit from support - use a stainless screw or tow into the wall or ceiling positioned so the head is in the middle of the plaster of paris. Bigger voids are often best filled by building up several applications of the plaster.

[lovesickest]

Hey everyone. My plaster repairs have been coming along, albeit much slower than expected. This was partly due to how unprepared I was for the physical exertion required - being a middle aged lady who reads books not lifts weights and all. I also discovered that as I got close to the wall and moulding that there were many tiny hairline cracks I could not see from the floor. Much skim coating ensued, then sanding, then more skim coating.

I think I have dealt with the worst of the crown moulding troubles. I was reduced to using my fingers to smear plaster along the curved surface into the worst cracks. I also used the plaster (pre-mixed joint compound - don't shoot !) like caulk between any gaps beside the moulding and the wall surface. On the worst, most fragile cracks I used fiberglass mesh, then several coats of finger smeared plaster to fully cover. I was using stiffer, somewhat drier compound that almost had the texture of modelling clay - and I was using it like clay.

I sanded yesterday. My secret weapon: a foam pool noodle cut to a 6" length wrapped in sandpaper. This worked beautifully to reach the deep inner curve. Today I primed with alkyd primer. There are still some dings and chips I am going back for - but the tinted primer also helped me to actually see the issues. My inner arms are screaming and burning though. They didn't feel so bad when I was up on the ladder priming but when I got down and they were at my sides - holy-moly. I hope this doesn't mean I have circulation troubles - only lack of muscles troubles.

Here are a couple of pics of today's progress. I am feeling quite okay about the results.

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[phil]

it looks nice i didnt't read all the plaster restoration techniques but one thing you can do to restore plaster is to make a lightweight frame ( cardboard box might do, and put a release on the plaster that is a good spot then take a mold off the good spot, then you can subsequently use this mold for repairs, by putting mold release on your newly made mold slap some plaster on where there is a broken missing chunk and push your mold up tight to the spot, the mold will fit tight and push the plaster into the contour, the same technique can be used to fix a broken plastic gear or perhaps something like an ornate piece of plaster where the technique you used would be very difficult due to the intricacy. a damaged plaster picture frame would be a good example of that. you make a plaster mold off the plaster where the plaster isn't damaged then use it as a form to make new plaster where there are parts missing.
Plaster of paris is good for this since it sets up so fast and no matter how thick you make it , it sets from the reaction not by drying. so it can be used to quickly make a make and female die or mold. you can use a layer of rubber cement to take the detail, and that "rubber lined mold" is more durable and reusable. paint the object with release, then rubber cement then make your mold which will support the rubber mold which is thin. another material you can use is the kind of plaster your dentist uses to make an impression of your teeth like if you were getting crown and bridge work done. well actually he would use a pink rubber stuff and put that in a tray to make the impression and then a set of teeth is made from that so the crown can be made to fit the upper and lower teeth. using the plaster teeth which are made from the impressions in the pink rubber stuff your dentist uses.

in restoring radios, sometimes knobs are missing but If I have one I can use similar techniques to make a knob from plastic materials that is identical to the missing one. In some cases it is necessary to make molds that separate, it depends on the shape of the object.

so for example the medialions in the corners of your door, they may be made of wood but if you had one missing it would be difficult indeed to make a wood one but you could quite easily replicate the missing part from one that did exist. the new part might be made of plaster not wood but could be painted to match and no one would notice. Judging by the trim you must have quite an interesting house !

[bfarwell]

Nice work!!

[lovesickest]

I am done ! (Except for a few tiny paint touch ups that will happen in the next 24 hrs.) Boy, am I sick of this room. I don't know if I will ever take on the chips around the edges - maybe if I have the time and determination to replicate the profile with a guide to build it up layer by layer ?

I painted the walls with a Benjamin Moore color from the historical color collection - Hancock Green - HC117. It is a slightly limier mint, in an eggshell finish . It looks great in the late afternoon sun - though it photographs more Crest toothpaste with my camera. I primed the walls, ceiling, and any plaster repairs on the moulding with alkyd primer, then discovered another week's worth of missed dings, pin holes, fine cracks, etc. that needed to get patched, sanded and primed as well. So much fussing. I painted the ceiling, crown moulding and wood trim with the same color - though I used alkyd semi-gloss on the wood trim, flat on the ceiling, and pearl finish on the crown moulding. I have spent some time laying on my sofa staring at the ceiling and walls - and there are no spots or areas that are causing me great anguish - so I figure it is fine. At some point, the previous owner had obviously stapled up plastic to keep out the winter drafts - so there were hundreds of tiny staple holes on the wood trim which were a devil to fill on such a complex profile. Those squeeze tubes of wood putty and fingers were the only thing possible to get at them. My brain has finally stopped seeing them. They felt like a roach infestation where I kept seeing another one from the corner of my eye !

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[Mick_VT]

It looks fantastic! I love that color pallette, very calming.

[Gothichome]

Very nice, well done.