I used crown white silk emulsion on superfresco wallpaper. This has dried extremely tacky. Why ? I have used emulsion on this wallpaper in my home and never had problems before. Think I usually by Dulux, but surely emulsion is emulsion. I always avoid the cheap stuff and stick to known brand. Don't want to do anything to make things worse as this is on my parents bedroom and they are in their 80's. Help!