if they are air bubbles i would suggest it is probably 1 of 2 things, either you didnt let the lining paper soak for approx 5mins before hanging or you didnt brush the air bubbles out from underneath the lining paper.
more likely too little paste than too much if you are getting air bubbles. eliminate this by giving an even and consistent layer of adhesive to the paper. use a sponge or brush or plastic spatula designed for the job to smooth the paper to the wall, eliminate air by applying pressure from the centre outwards.
sizing the walls will help as well. and periodically check the paper as it's drying for bubbles. glue bubbles are usually fine and will flatten as they dry out. air bubbles can be removed for some time afterwards whilst the glue is still wet.
you can apply the adhesive with a roller to the back of the paper. it helps to get consistency but is messy. i prefer a brush. and only paste the wall if you are using paper specifically designed to be hung that way. lining paper would usually have the paste applied to it rather than the wall.
air bubbles can be treated after drying if still present by injecting paste into the bubble using a syringe then pressing flat. don't forget to remove any excess paste.
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