Replies

1. 
   aschweic | Jul 07, 2004 05:20am | #1

   I have worked here along the South and North Carolina Coasts with several contractors that have used it or one if Dow's competitor's equivalents (I think Pecora or Sto's).  Its a good silicone elastomeric with high permeability.  The two buildings I spec'd out Sto's version still look brilliant white after several years.  It seems it is less prone to dirt sticking to it and then mildew growing on it.  I think the drawback to it (if you want to refer to it as a drawback) is that once you coat with silicone, you have to stay with silicone when you need to recoat in several years since other non-silicone elastomerics won't stick to it.

   Al in SC

1. 
   Piffin | Jul 07, 2004 05:55am | #2

   "...with high permeability. "

   Did you mean to say high resistance to permeability? I can't imagine wanting to use a coating that is highly permeable since the idea is to keep water out. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

1. 
   aschweic | Jul 07, 2004 04:21pm | #4

   I didn't make myself clear.  I meant high vapor permeability.  It allows the passage of water vapor, not water liquid.  High permeability to water vapor is a good thing if you are worried about moisture drive from inside the building to outside.  If you have a low perm coating, it might blister and peel under vapor drive from inside to outside.

   Al

2. 
   BillHartmann | Jul 07, 2004 04:40pm | #5

   While you concern might be taken as right based on the "generic" meaning of permeable;

   Main Entry: per·me·able

   Pronunciation: 'p&r-mE-&-b&l

   Function: adjective

   : capable of being permeated : PENETRABLE; especially : having pores or openings that permit liquids or gases to pass through <a permeable membrane> <permeable limestone>

   But whenever I have seen the used in construction it has been many been restricted to moisture transfer and not liquid transfer; i.e. "perm rating". For example the ideal building wrap/paper has a zero water transfer, but high moisture permeablility.

   But it is also best to make it clear and spell it out.

   Found this on buildingscience.com that is both approprite to this thread and a good example how to use the term with percission.

   "January 2003: We know more about how elastomeric paints work--or more precisely,

   about how they don't work--on stucco exteriors, particularly in hot-humid climates.

   Accordingly, make or note the following correction:

   EEBA Builder's Guide - Hot-Humid Climates (2000 Edition), Chapter 9 - Masonry Construction, page 256:

   Replace the 3rd complete paragraph with the following two paragraphs:

   "On exterior stucco surfaces, water repellant vapor permeable and semi-vapor

   permeable coating or paint systems are recommended. Recall that

   water vapor flow occurs from both a higher concentration to a lower

   concentration and from the warm side of an assembly to the cold side of an

   assembly. A rain wetted stucco covered masonry wall that is heated by solar

   radiation will be warmer and wetter than both the interior and the exterior

   air. Drying will be both to the outside and to the inside. A heavy coat of

   impermeable paint over exterior stucco will blister under such conditions.

   The more vapor permeable the exterior paint coating, the better under such

   circumstances. Acrylic latex paints formulated for exterior use are

   recommended for almost all stucco applications.

   Acrylic latex paints generally outperform "elastomeric" paints over stucco

   renderings due to the lower permeability of the elastomeric paints.

   Elastomeric paints have excellent crack spanning characteristics, but give up

   a degree of permeability to achieve the crack spanning ability. If water

   enters the stucco rendering at a joint or reveal or flashing or flaw,

   elastomeric paints have been known to blister. Elastomeric paints should be

   reserved for special conditions where substrates are severely cracked and

   crack spanning coatings are necessary and no other coating approaches are

   practical."

   Joseph Lstiburek"

1. 
   Piffin | Jul 08, 2004 02:56am | #6

   Thanks guys, my background is in roofing and underground water proofing and we always looked for a low perm rating. Not good to let a lot of water pass through a rubber roof or a foundation coating. hadn't hear d it used in a positive manner. 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

2. 
   jimblodgett | Jul 07, 2004 01:57pm | #3

   Thanks, Al.  You're right about the adhesion problems of paint over this stuff.  I'm a little concerned that a future owner will get sold a paint job unaware of the mess they'll be getting into. 

   Apparently they're selling a lot of this stuff to cover Drivit with, but on a single family dwelling, there are other considerations. 

   Sounds like a good product, that's for sure.  Sealants have sure come a long way in the past 30 years.

2. 
   oops | Dec 18, 2011 06:31pm | #7

   coatings

   Yeah, like hankering, why drivit?  I thought the post was about real stucco.

   One of these days I will learn to check the date on the original post before opening my big mouth.

1. 
   DanH | Dec 18, 2011 06:33pm | #8

   Do you guys realize that this is a 7-year-old thread?