Repairing a section of plaster cornice

[tony]

Afternoon All,

I have just spend 4 hours removing a section of plaster cornice from around my lounge bay windows.

Why?

Well my windows are completely ruined by neglect for 30 years+ and house being empty for 2+years, I am replacing the windows with new sash and case windows.

Originally windows were put in to make property watertight and then plastering/ cornice work took place, unfortunately for me part of the wood about 2 " goes behind the cornice.

I have carefully removed this with a fine diamond tipped disc on a 4"grinder along with a pad saw and gentlemans saw.

Now i am left with the task of refitting the cornice after the installation of the new windows, i was quoted £2000 to do this work, were are taling about 5 ft of cornice, so thats why i got the tools out.

I am now left with 4 sections that i need to fix back into place, can anyone suggest a solution.?

Can I use wet plaster of paris to join the parts together, with support until it goes off and then fill the 3mm cut mark made by the saw?

I have tried looking for plaster of paris online but no luck any help on thatg would also be grately appreciated.

Best Regards

Tony

 

[Gervase]

Try looking for what's called casting plaster. I know Ty Mawr sells it in two grades - coarse for general casting and fine for fine detail.

 

[BMcD]

Casting plaster and plaster of paris are the same thing. If you can wait a few days I'll post the method of running a cornice in-situ with pics if I can figure out how (posting that is not the plastering)

 

[tony]

Hi,
Thanks for the offer of showing me how to run in situ, but i have seen it done before. thanks anyway.

Because in took great care in removing the sections, it can go up agin, i made sure i cut it between dental work as not to give myself to difficult a job reinstating.

Do you think plaster of paris would be ok to hold original piece back in place ?

Regards

tony

 

[Gervase]

PoP sticks like sh!t to a blanket, so it should hold the original stuff up nicely. Just score the mating surfaces first.
I know it's a modern bit of chemical cheating, but if you really want to stick something, then 'Sticks Like Sh!t' in tubes from your local builder's merchant is pretty awesome. Just a shame about the name - it must put an awful lot of vicars off popping into Jewsons for a tube!

 

[Cardiffbloke]

Can i ask some advice please? I know nothing of this cornice work and have in the course of renovating my house damaged some sections of cornice work. plus there is old damage inherited..... How do you go about repairing it, eg making a mould of existing plasterwork then making and sticking new stuff up..... PLEASE explain in 'Janet and John' terms as i am thick!

 

[tony]

Lets assume a small damages section of cornice, with no dental work etc.

Get a saw and cut a vertical cut into the good part of the cornice, fairly deep.

Now get a bit of thick card and insert into cut.

Mark profile of coving onto cardboard with pencil.

Transfer cardboard profile onto thick plastic, tin or some rigid material.

Apply plaster of paris to damaged section, pull profile across wet plaster to form shape, this will take a couple of goes,

Patch cut mark with new P.O.P area might need a sand with smooth sand paper.

regards

tony

 

[Gervase]

...and, for egg and dart or other decorative coving with a repetitive pattern, you need to use tony's technique with the addition of some silicone moulding rubber. Make the cuts at a logical place for the repeats in the pattern, paint the plasterwork with a release agent (or use a silicone spray) and then apply the silicone gloop, using bits of card and offcuts of wood as stiffeners once a couple of layers have been applied and become tacky.
When fully cured, peel it off, place card or plastic sheet at the ends of the moulds and use for casting new sections.

 

[Nigel Watts]

Pure Plaster of Paris is very runny. I prefer to mix Plaster of Paris with some lime putty to make the adhesive/repair material. To make it strong enough, use Herculite rather than casting plaster (Herculite is a stronger type of PoP), and make sure the mix has at least 50% PoP in it. Damp both the wall and the section of moulding well first to reduce suction.

 

[BMcD]

Not ben able to make time to post a method for cornice repair but in the mean time here's an interesting paper

http://www.ihbc.org.uk/context_archive/64/irish/plasterwork.html

 

[Lime]

You can buy plaster of paris at Boots.

 

[Cardiffbloke]

Pure Plaster of Paris is very runny. I prefer to mix Plaster of Paris with some lime putty to make the adhesive/repair material. To make it strong enough, use Herculite rather than casting plaster (Herculite is a stronger type of PoP), and make sure the mix has at least 50% PoP in it. Damp both the wall and the section of moulding well first to reduce suction.

So that is 50% Herculite POP and 50% Lime Putty? Where do you get these 'ingredients'? Thanks CB

 

[Cardiffbloke]

Oh yes..... and what on earth is dental work?> you guys have to remember that some of us have no idea what you mean when you use these 'in' terms.... I am a completely clueless moron when it comes to such things but a willing 'have a go' sort.... thanks again CB :?

 

[Gervase]

Dental work is cornice with fancy mouldings along the edge - teeth, zig-zags, egg-and-dart and the like - as opposed to straight-run cornice.
Like this

 

[dandrew]

Dental work is what you have done to your teeth .

In contrast dentil moulding is a series of interuptted rectangular or square blocks that can look like teeth, well cartoon ones anyway.

 

[Penners]

You can buy plaster of paris at Boots.

What an incredible coincidence. You can also buy boots in Paris.