How to seal plaster before wallpapering?

[Rattitude]

My house is from the 1920s.

The plaster on one wall must have been painted blue at some stage.

Some blue stains have appeared on the wallpaper. The decorator came again, sealed the wall and wallpapered again. The blue stains have reappeared. Grrrrr...

Now, I had had the exact same problem with my previous wallpaper and the decorator at the time must have sealed the plaster with something good because the problem never reoccurred, so there must be a product out there that does a good job at sealing the plaster.

Could anybody recommend a product that would work?

stain block. Looks like white paint.

Decorating shops will have it.

I usually like to paint bare or patched plaster with white paint even if not stained, it gives an even colour and absorbency and prevents patchiness showing through.

I usually like to paint bare or patched plaster with white emulsion prior to the real decoration...

Do you thin the emulsion (for bare plaster) Piglet John?

on bare plaster, including filled or patched areas, yes, one or two mist coats thinned with water and brushed on, then subsequently apply undiluted, mostly with a roller.

painting the wall white will highlight to your eye any remaining blemishes, which you can correct before the more expensive decoration.

Thanks, PigletJohn. I have done a quick google search on stain block and a few options come up with varying prices.

Is there one you brand you would particularly recommend? I would be happy to throw some money at it, if need be, just to prevent the problem from ever reoccurring.

Oooops! Is there one brand...

if there is a branch near you, you can order and collect this cheap one Cheap paints often need two coats.

You will probably find International or Dulux/Polycell brands in the High street which should be good. You will find spray cans which are much dearer. International tend to attack the "specialist" paints DIY market where there is less competition. Their cans are usually red. Wilkinsons carry them, and I think Dyas. Dulux has been bought up by a foreign maker and some say the quality has dropped. Wickes is not highly thought of.

Homebase sell the Crown one.

If there is a proper decorators supply shop near you, they will have a couple of good ones from a big name, and also something cheap that will not be so good. I would be happy with any of the major brands and would just apply an extra coat if I thought coverage was poor.

Ok, thanks a lot, PigletJohn. Your advice is much appreciated!