Ask The Expert

There are two main reasons for this: either the tape was not pressed firmly home, or there was too much joint filler under the tape.

To rectify the problem open up the blister by cutting and folding back the tape.  Refill the join and then press the tape back into position.
   

This problem is usually caused by the joint cement or filler being mixed too wet, or drying too quickly.  This is especially likely in extremely hot, dry weather or freezing conditions.

To remedy this, cut away any poorly bonded tape edges and loose compound, then retape.

Avoid this problem in future by carefully following the mixing instructions on the sack, and if possible avoid working in extremes of temperature.
  

The main causes for this are the mix being too wet, and insufficient drying time between coats.

Be sure to follow the mixing instructions carefully, and allow adequate time between coats for the product to dry.