Replies

1. 
   RSRose | Nov 13, 2002 03:42am | #1

   DHoov,

   Yes, you should seal the plywood. I don't think that formaldehyde is a concern. But unless you seal it, it will smell of other reasons. It will absorb moisture and can grow mildew. The raw wood will smell even if nothing's growing in it.

   Seal it with a couple of coats of shellac or use either an oil-based or latex paint. Sealing it will make it much easier to keep clean, also.

   R

2. 
   DWRead | Nov 13, 2002 04:21am | #2

   You  may wish to read up on sick-house syndrome.

1. 
   RSRose | Nov 13, 2002 04:42am | #4

   DHoov,

   I'll repeat my earlier advice that you don't need to worry about problems with a single sheet of plywood used the way you describe. Living in a house entirely constructed of formaldeyde products and sealed against ventilation for long periods of the year is an entirely different matter.

   Paint the wood with shellac or non-toxic paint and you will be fine.

   R

3. 
   StanleyNiemiec | Nov 13, 2002 04:32am | #3

   Formaldehyde is used in the assembly of plywood and consists primarily two resins  --  phenol-formaledhyde and urea-formaldehye. 

   Phenol-formaldehyde [PF] is a water proof resin that is used in exterior grades of plywood (read as construction grades).  From my limited understanding of adhesives chemistry,  the bonding process is efficient and unless the adhesive is improperly mixed, it is not necessary to have an excess amount of formadehyde present to create a suitable bond.  And once the bond has been created, it is relatively stable.

   Urea formaldehyde [UF] resins are water resistant (not water proof) and they are used primarily for interior panel products such as hardwood plywood.  The creation of the urea-formaldehyde bond is not as efficient as with phenol formaldehyde resins and as a result, producers of the panel products added an excess amount of formaldehyde to create a suitable bond.  This meant that for a period of time after manufacturing, off-gassing of the formaldehyde occurred -- obviously dependent on the amount of formaldehyde present and the concentration gradient with ambient conditions.

   The primary reason for resin choice is cost  --  phenol formaldehydes are more expensive than urea formaldehydes.  And if the product will not be exposed to repeated wetting and/or high moisture contents, it is generally unnecessary to have water-proof properties.

   Formadehyde is nasty stuff  --  remember those poor frogs from biology that took their final swim in it.  It is a very effective preservator.  Humans don't necessarily like it either (I think it was used as embalming fluid).  Formaldehyde can cause allergic reactions in some individuals and over time, others can be sensitized to it (and thus causing allegic reactions).

   Formaldehyde exposure became a real problem for the general public in manufactured housing products  --  the tightness of these dwelling and the sheer volume of interior panel products meant for some very elevated levels of formaldehyde were present.  Industry wide off-gassing standards have been established (but that does not in any way imply that formaldehyde off-gassing has been eliminated).  The resin formulations have been changed but to a degree the problem still persists.  I am several years out of date on actual current practices and standards so if somebody has more accurate, up-to-date info, please share!

   Sealing the panel with finish is not a cure all.  All finishes are porous (correlated with their Moisture Excluding Effectiveness [MEE] values) so that a coating will reduce the transmission/off-gassing rate (leading to lower levels of interior concentration levels) but in doing so extends the period of time for the off-gassing.

   Whether a panel product has a UF or PF resin is difficult to ascertain.  Exterior flakeboard and OSB are likely to have a PF resin.  Whether an MDF or particleboard panel is one or the other is more difficult to determine.  If in doubt, this is one area where an MSDS sheet should help you make that determination.  If a business is selling the stuff, they SHOULD have a copy and you can generally glean enough information from it to make an informed choice.