[SPAM] Re: s 40-80 and 40-20

[Guest guest]

please do your homework.

no coating/paint/encapsulant is "like Tyvek" -- not even close!

40-20 (per mfr technical data sheet)

wet film thickness: 20 mils; dry film thickness: 11 mils; permeance: 6 perms at 11 mils DFT

Tyvek: (Spun bonded polyolefin, 0.006 in., 0.013 lb/ft2)

~70 perms (per the mfr, slightly less than 70; per ASHRAE ~76 perms)

other building materials of interest:

1/2 inch gysum wallboard: 55 perms at 50% RH

one inch of still air: 120 perms (the reference point)

6 mil poly sheeting: 0.06 perm

typical latex paints at 1-2 mils DFT: 5-8 perms

1/2 inch OSB: ~0.6 perms at 50% RH

1/2 inch plywood: 1 perm at 50% RH

those quoted "at 50%" demonstrate variable permeability based on installed conditions.

for more see: 2005 ASHRAE Handbook of Fundamentals, Chapter 25

also see: ASHRAE Research Project RP-1018, "A Thermal and Moisture Transport Property Database for Common Building and Insulating Materials", July 2002

Wane

<><><><><><><><><><><> Wane A. Baker, P.E., CIH Division Manager, Indoor Air Quality MICHAELS ENGINEERING"Real Professionals. Real Solutions." St. , La Crosse, Milwaukee

Phone , ext. 484 Cell Fax

mailto:wab@... On the web at: http://www.michaelsengineering.com

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>> ,> > Good points to bring up. Since we are being specific to 's 40-20, when> a contractor appropriately applies 40-20, the mil-thickness after drying and> curing is greater than 6-mils. Meaning, it is put on at 10-mils and dries to> 6-mil thickness (+/- a percent or two depending on the surface, absorbency,> temperature, RH, etc.)> > 's 40-20, properly applied I believe exceeds a PERM-rating of more> than 1. > > Moffett > > > > From: iequality [mailto:iequality ] On Behalf> Of Geyer> Sent: Tuesday, June 12, 2007 9:42 AM> To: iequality > Subject: Re: [sPAM] Re: s 40-80 and 40-20> > > > Pat:> > Let's not be too hastly to blame all encapsulants for vapor-lockup. Some> encapsulants have a PERM rating greater than 1.0, therefore, they would be> classified as a vapor retarder (like Dupont's TYVEK House Wrap) and not a> vapor barrier (like 4mil poly sheeting). However, your point is well taken,> and it is an issue to be reckoned with for all coatings, not just> encapsulants, i.e., are they compatible with the building assembly/system to> which they are applied? This is where the mustard meets the road regarding> folks that know building systems versus those that don't, i.e., material's> science.> > For what it is worth....> >