Expert: Bruce E. Johnson - 3/24/2009

Question
I have a 12'X35' exterior lanai that has a smooth textured drywall ceiling.  The home is in SW Florida and is about 12 years old.  All of the taped joints are cracking and the new joint compound I applied is falling off. Is there a special joint compound I should be using?

Answer
Hi Herb, sounds like you need a different type of drywall mud.  The "setting" type of mud works better for exterior applications because it isn't so affected by moisture.  I'm sure you have probably seen this mix in the Home Depot or Lowes it is the drywall mix that has a number on it 15, or 45, or 90.  This kind of mud reacts with water and air and actually sets up like concrete instead of air drying.  Because it sets up you need to be ready to do the work in the alotted time.  For joint work and large areas you should use the 90 minute mix.  This gives you 90 minutes before it sets up.  To speed up the joint taping process I use the fiberglass mesh joint tape.  It has a sticky back on it.  I stick the tape to all the joints first.  Then I mix up the amount of mud I think I can use in 90 minutes and go for it.  Cut it tight, in other words, try to keep it as smooth as possible when applying it.  Once it sets up it will need to be sanded between coats.

Once you get the taping done with the new setting drywall compound you need a good paint job.  Always use a primer first and let it dry properly before applying at least two coats of a good latex or elastomeric paint..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com