ACI 350 sealant question

[Dennis59]

There seems to be a slight contradiction in ACI350-06.

R4.8.3 — Sealants
"Non-sag sealants are recommended for submerged service. Polyurethane sealants, single-component, and two-component are recommended. Polysulfide sealants are not recommended when the sealant is in contact with wastewater."

G.3.4.1 — Polysulfide sealant
"Polysulfide sealant shall be a two-component elastomeric compound meeting the requirements of ASTM C920 and shall have permanent characteristics of bond to metal surfaces, flexibility, and resistance to extrusion due to hydrostatic pressure. Air-curing sealants shall not be used. Sealant shall be a type that is appropriate for submerged service when used in fluid storage tanks."

I am surprised that the main body of 350 specifically warns against polysulfide for wastewater contact, and yet Appendix G (wire-wrapped precast tanks) specifically asks for polysulfide in a submerged condition. Appendix G is probably most-often used for potable water tanks, but could also be used for wastewater, I suppose.

There is probably something obvious that I am missing here.

Can a sealant expert offer a recommendation as to whether polysulfide sealant is good in a wastewater environment?
Does it make a difference submerged vs non-submerged?
I have a current concern with sealing concrete joints in a non-submerged wastewater application with high H2S levels.
Thanks for any advice you care to share.

 

[Ron]

The potential for sealant deterioration for polysulfide sealants (ion exchange, repolymerization, direct reaction) is greater in wastewater than in potable water.

 

[JedClampett]

We design water and wastewater facilities and only have the two part polyurethane sealants in our specifications. I think the polysulfides are an older technology and not as good.

 

[dik]

Depends on the use. Polyurethanes require a more 'pristine' application whereas polysulphides tend to be more forgiving. Polysulphides are contraindicated for some environments. They are also older technology.

Dik