galvanized vs. coated

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Author Message Lynn Javoroski Senior Member Username: lynn_javoroski Post Number: 91 Registered: 07-2002 Posted on Thursday, April 08, 2004 - 01:01 pm:    Does anyone have an opinion about or know of a source for reliable, unbiased information comparing the performance and cost of galvanized railings with an alkyd enamel coating versus zinc primer/high performance epoxy/polyurethane coating? Or other options, for that matter? These railings will be exterior, on a river (so water, but not salt water). The project is multi-use (commercial/condominium) and public (river walk). Thanks in advance. Anonymous   Posted on Thursday, April 08, 2004 - 04:02 pm:    Hot-dip galvanizing, while more expensive, will coat the inside of railings too, while zinc primer, obviously will not; as we all know and see so often, corrosion works it way from the inside out. Alkyd coatings will be much easier to repair paint film damage (scratches, nicks, chips, etc. because they are relatively "softer" than epoxy/urethanes). Epoxy/urethanes will be more abrasion-, chemical-, and fade-resistant...also much more expensive and more difficult to repair than alkyds. Richard Hird (Unregistered Guest) Unregistered guest Posted on Saturday, April 10, 2004 - 10:08 am:    Agree with Anonymous except I am not so sure he is right about cost. In an area like ours, where galvanizing is readily available, (.$0.70/ft for a 1.5" sched 40 pipe) it is definitely cheaper than an equivalent primer. For the condition in the above discussions I would only specify an inorganic zinc primer and require at least a SP6 surface preparation @ $0.50/ft plus painting @ $0.45/ft = $0.90 per foot for a 1.5" sched 40 pipe for a 1.5" sched 40 pipe. It is also probably cheaper than organic zinc primers with the topcoats listed in the above discussions, although I have no specific information on this system. Anonymous could be correct 1) if you add a high performance decorative topcoat to the galvanized pipe, 2) you are in an area without local galvanizers, or 3) if he is thinking of a universal zinc filled primer requiring only power tool cleaning. However the latter is not equivalent to hot dip galvanizing with respect to its life cycle cost. Stephen H. Falk Senior Member Username: shfalk Post Number: 8 Registered: 08-2002 Posted on Sunday, April 11, 2004 - 09:17 pm:    You should take a look at the "duplex coating" systems offered by the good galvanizers. It combines the best of both worlds - hot dip galvanizing and shop finishing. Tracy Van Niel Senior Member Username: tracy_van_niel Post Number: 77 Registered: 04-2002 Posted on Monday, April 12, 2004 - 07:37 am:    Are you refering to a high performance epoxy/polyurethane coating similar to Tnemec or Carboline? If so, there are times when we have specified that instead of galvanizing. Surface preparation is the key to the success of the coating. We specify it in a separate section from the regular painting system. Part of the problem though is making sure that when maintenance comes around, they don't go back over the "special" coating with the latex paint that they picked up from the local homebuilders store. Stephen H. Falk Senior Member Username: shfalk Post Number: 10 Registered: 08-2002 Posted on Monday, April 12, 2004 - 09:17 am:    No! This is a system involving preparation, galvanizing and then coating within 12 hours, it does incorporate the high performance coatings. As far as maintenance goes - it is the same with anything! This system belongs in a Division 5 section developed for galvanizing and galvanizing with duplex coatings. It is available from any of the AGA members. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 209 Registered: 03-2002 Posted on Monday, April 12, 2004 - 11:27 am:    We have used the system described by Stephen Falk here in New England. Due to our climate, this type of coating is well worth the modest additional cost. The galvanizer here (there's really only one in New England) uses a high-performance primer and top coat. I, also, like the fact that as anonymous points out, the galvanizing gets inside the pipe too. Stephen H. Falk Senior Member Username: shfalk Post Number: 11 Registered: 08-2002 Posted on Monday, April 12, 2004 - 09:34 pm:    John: Take a fresh look, there is a new and experienced player on the scene to give some competition to Duncan; its' refreshing Richard L. Hird (Unregistered Guest) Unregistered guest Posted on Tuesday, April 13, 2004 - 09:27 pm:    I take issue with John's and Anonymous' contention that galvanizing the interior is important. On sheet metal (your car) they are correct the steel is too thin. On thicker steel rust becomes self protective. It is works just like CORTEN, provided the rust is not subjected to a moisture wash. Since I am not a NACE engineer I cannot state this unequivocally, but I suspect that the inside of a Sched 40 pipe will rust, but it will not corrode through to the opposite side in any reasonable time framework. John McGrann Senior Member Username: jmcgrann Post Number: 16 Registered: 03-2002 Posted on Wednesday, April 14, 2004 - 11:55 am:    You might not need to coat the interior of a schedule 40 pipe for corrosion protection, but dipping a sealed section of pipe into molten zinc doesn't make too many friends in a galvanizing plant. To avoid having the galvanizer burn vents and weeps in pipe rails to keep them from exploding in the tank I specify that the fabricator drill all required vent and weep holes prior to galvanizing. Filling the holes with solder following galvanizing is optional. Anonymous   Posted on Wednesday, April 14, 2004 - 12:23 pm:    Mr. McGrann, Aren't you specifying "means & methods" rather than "end results" (e.g., ventholes shall not occur in readily visible surfaces...)? Anonymous   Posted on Wednesday, April 14, 2004 - 12:52 pm:    Regarding Mr. Hird's comment: About costs, by AGA's own "admission" (pubs on their website), HDG is more expensive that all but the cheapest/cheesy paint primers. But if in your area, HDG is "cheaper", I'd say go for it, as I'm a believer that galvanizing has a distinct corrosion-inhibitive advantage over zinc primers. About the inside of railing, it too is subject to similar corrosion environment that the exterior surface that you're protecting with zinc primer is; given the situation that Anne described (river water exposure, which I foresee relative high humidity constantly), it only "additionally" validates advantage of HD galvanizing (vs. zinc primer). Besides, car sheet metal is thin(ner than in '50s) to save weight (among other reasons, e.g., sell more replacement parts); if thicker, it too would not rust-thru...as fast. John Regener, AIA, CCS, CCCA, CSI, SCIP Senior Member Username: john_regener Post Number: 163 Registered: 04-2002 Posted on Wednesday, April 14, 2004 - 02:19 pm:    See http://www.gaa.com.au/benefits.pdf for an explanation of how galvanizing works and also the relationship with paints and coatings. John McGrann Senior Member Username: jmcgrann Post Number: 17 Registered: 03-2002 Posted on Thursday, April 15, 2004 - 08:03 am:    Regarding the "means and methods" comment by Anonymous No. 2. When presented with a fabrication that contains a concealed and/or sealed space the galvanizers in our area will not hesitate to create their own vent holes using a cutting torch if the steel fabricator doesn't provide them. They are not as concerned with appearance or finish as they are with venting trapped air and draining molten metal. I've seen results of burning holes with a torch that were so rough they were flagged by a building official for failure to meet code requirements for surface smoothness. This particular “result” held up a temporary occupancy permit. If the fabricator or galvanizer can show me they can create a hole with an appearance and finish equivalent to drilling using some other method I'm all for it. My clients expect my specifications to produce results that allow the contractor to achieve compliance with various requirements, including building codes. If I have to prohibit a certain technique to do so, then so be it.