Which undercoat for old cornicing?

[ruthierhubarb]

Hi. We are decorating our hall (victorian house) which has very intricate old plaster coving. This has previously been painted with what looks like ordinary vinyl emulsion. We sugar soaped and rinsed it, and have applied a water based undercoat (B & Q colours undercoat and primer) but it is very patchy and has not covered well at all. We applied a coat of the (colours quick drying satin) topcoat on a small patch today just to see...but it also looks patchy....

Read somewhere on here yesterday about using oil based undercoats instead, and wondered whether this would be a better option even if we are are not planning to use gloss? All a bit confusing. Very grateful for any help, and i may be on here a lot over the next few months!. Trying to keep costs down by doing it ourselves but its scary stuff for beginners!

By the way it would be really helpful if we could have a favourites folder for articles or posts from others that we have found useful. I have spent hours today unsuccessfully trying to re-find one I saw yesterday.

 

[TheDec]

Oil based undercoats are not only recommended to act as a base for a particular paint system but also as a preventative measure with regard to something that may tend to bleed through future paint systems.

What I would have suggested here would be to remove the sheen from the existing cornice using wire wool then to dust off and apply a coat of oil based undercoat prior to further decoration. In this situation if a water based paint had been used there would be probabability that any wire particles left behind would rust and in time work their way to the surface, That would be one reason why an oil based undercoat would have been suggested.

In you situation now I would apply a thinned coat of matt emulsion before you continue and with any luck everything will turn out ok.

Dec

 

[ruthierhubarb]

Thats great thanks, we have old coving in a number of rooms so will definitely try your suggestions there. How much should we thin the matt emulsion by the way?

 

[TheDec]

Around 20% water should be fine.

Dec

 

[ruthierhubarb]

Thanks again - you always seem to give very helpful replies to others by the way! Much appreciated.