wall sizing - new plaster

[Tom]

Hi All,

Just wondered if anything has changed over the years - I always understood that new plaster needs to be sized with PVA or equivalent before painting etc., failure to do leads to peeling later on. Uneven peeling at that, I've seen this so many times its unbelievable, there must have been loads of inexperienced painters/builders/finishers in the past. Trouble is the problems won't show up for years, by which time they will have legged it.

But the current builders I'm using deny sizing is needed. Why? What has changed? Have newer emulsions made this unnecessary?

Rgds., Tom

[Invisible Man]

Most recommendations seem to be for thinned non-vinyl emulsion for first coat straight on to dried plaster. Some sheds do it ready to apply.

[Phil L]

Bare plaster needs to be sized, although your reasons for doing so seem to differ from the actual reason. paper shouldn't peel regardless of whether the wall was sized or not - sizing simply kills the suction of new plaster, making it easier to 'slide' the pasted paper into position without the wall drying it out too much during hanging. Painted walls don't generally need sizing because they are effectively already sealed.

If your new plaster is being left raw, you need to size it, you can use normal paste diluted down from the usual consistency, and allow to dry before paperhanging

[Mike P the 1st]

On Wed, 03 Mar 2010 13:50:06 GMT, "Phil L" gently dipped his quill in the best Quink that money could buy:

I understood he was asking about painting walls ..not papering.

Mike P the 1st

[NT]

If emulsion is put onto new plaster, the plaster sucks the liquid out of it, and the liquid contains the pva glue that sticks the paint pigment on. So you get a weaker bond of paint to plaster.

There are 2 ways to address this.

1. Paint first with paint diluted 50/50
2. Paint first with just water, and after 5 minutes apply full strength emulsion.

Both work fine, I find the latter much quicker.

nt

[geraldthehamster]

Size before papering, but not before painting.

I'd start with thinned emulsion if painting.

There's loads of discussion and information on this group, and almost every other DIY group or forum on this, just search for "new plaster". Loads of controversy over how much to thin the paint by, and what paint to use, but consensus that you don't PVA plaster if you're going to paint it.

Cheers Richard

[Rick Hughes]

as others have said a 50:50 thinned first coat of emulsion will do.

Formulations of paint change