Preparing old cornice for re-painting

Hi All
I have just stripped all the old plaster from my brick walls ready for re-plastering. but before that I want to prepare the old ceiling and cornice. Where the cornice formed a bond with the wall with the old plaster now there is a gap and the old cornice rough to run your finger along the underneath. What prep work is best to get a smooth finish on the cornice where it will butt to the new plaster, orbital or hand sanding..? Also some of the plaster has fallen from underneath the cornice will this be a problem when re-plastering..?
cheers

j

Hi Railman,

You have got a bit of a nasty situation there. I presume you will be sticking new plasterboad to the brickwork with cornice adhesive?

I would only use a hand sander, because the vibration of the orbital sander may cause damage to the cornice.

Go to a plaster supply company and buy flexible foam sanding blocks they would be ideal for that purpose.

The next issue you face is getting the new plasterboard to marry up with the old cornice and finishing the junction.

Old render can vary in thickness 20mm to 30mm where the plasterboard with the cornice adhesive will total about 15mm leaving you with an excessive margin along the cornice line.

You can solve this by placing plasterboard blocks along the cornice line stuck on with cornice adhesive to act as a backing say 15mm back in from the back edge of the cornice. You may find that you wil need to put blocks on the entire wall to level the sheets. When the board is stuck to the blocks the line will be acurate along the cornice.

How you go about it will depend entirely on the thickness of the old render.

You may find battening the wall is preferable than sticking with cornice adhesive, again this will be dependent on the render thickness.

At the top where the sheet meets the old cornice you can be face with several scenarios. The best result would be the sheet slipping in behind the cornice leaving a 2mm gap. That gap would be best filled with a paintable sealant. Getting the sheets to fit that well will not be that easy.

It is more likely that you will have at least some gaps between the bottom edge of the cornice and the top edge of the sheet. These gaps can be pre-filled with a base coat or cornice adhesive then scraped back level. I would then "flat" tape along the top edge with paper tape. Then after sanding run a small bead of paintable sealant along the cornice wall junction.

I have made a couple of diagrams that show what I mean I hope they come up ok.

Sorry they have rotated slightly for some reason I don't have the time right now to correct them. I think you wll get the idea though

Cheers Rod Dyson

Hi Rod

Thanks so much for the reply. The plan is though, to re-plaster the walls with wire mesh then a render then a top coat...why you may ask..? I think the main reason is I just like the look and feel (Solid) of plaster and I think it gives a better finish for the paint as well. Also I want to try and keep the originality of the 1927 Californian Bungalow. Tell me if I am asking trouble doing this...? With the mesh and render and top coat should that bring it back in line with the cornice..? I'm not to concerned about a dead flat finish just one that is smooth and looks original.

Cheers

j

Ok you will get a good finish with the rendering, as they will just work to the original thickness.

But clean up the bottom edge with a hand sander only!

The situation I have describe above is a common one, so others reading this post should be able to benefit from it.

Cheers.

Rod