Home /
T.O.C.
FAQs
 
Good
Books
Ref.
Libr.
Advertise
Here
Help
Wanted
Current
Q&A's
Search 🔍
the Site

Chime right in! (no registration req'd)

-----

"Rusted sheet metal HVAC ducting"



Current question:

September 4, 2021

Q. When I bought the house, I had noticed this rust-like stuff on the end of the HVAC duct work but I want to make sure that it's just rust and not mold.

33689-1a   33689-1b   33689-1c  

So I'm curious what the yellow stuff is? How do I clean this? Or does it need to be removed and replaced? Thank you.

Dylan Bruns
- Saint Louis, Missouri
^


September 2021

A. Hi. The orange color looks a lot like rust to me, but rust doesn't make lumps of that sort. I'm not sure from the photos if I am looking at pebbles stuck on the sheet, perhaps from this sheet sitting on wet concrete before erection, or if those lumps are an orange colored mold.

You might take a look at
https://www.bustmold.com/resources/about-mold/types-of-mold/orange-mold/
because in person you may be able to see something that I can't grasp from the photos.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related Q&A's, oldest first:

2005

Q. My home furnace is in a crawl space, & some of the sheet metal ducting has developed rust in spots in low-point areas of soil contact, unnoticed until recently. I have removed the offending soil, but need to know how best to treat the rusted areas. The rusted areas are close to the furnace and are visible and accessible when I remove the filter cover to replace the filter. Removal of the ducts is NOT within my personal capability, so I will have to do any work from inside----when the furnace is secured, of course. Any recommendations on how best to proceed?

JOHN WALKER
HOMEOWNER - LEESBURG, Virginia
^




2005

A. Use sandpaper or 0000 steel wool [affil. link to info/product at Rockler] to get the rust off (or a commercial solvent) paint with furnace/fireplace paint (available at most home improvement stores).

My above suggestion is based on the guess that the rust is due to overheating of spots on the ducts. If these same ducts also run your cooling, I would suggest using a different pain (but still sanding the rust off for first step on surface prep). Use an epoxy based paint if it is due to excessive moisture.

Put some thought into what could have made these rust spots, was it high moisture? Excessive heat? poor plating? the magical duct gnomes?

The more we know the more that we can suggest.

Marc Banks
- Elizabeth City, North Carolina
^


2005

Q. MARC BANKS,

THANKS FOR YOUR RESPONSE. THE DUCTS ALSO SERVE MY AC, & THE CAUSE OF THE RUST WAS MOST LIKELY MOISTURE FROM THE SOIL CONTACT, AS IT OCCURS ONLY IN THOSE AREAS. I CAN REACH MOST OF THE AREAS FROM INSIDE, AND WILL BE ABLE TO SAND THEM, BUT WILL NOT BE ABLE TO REACH ALL OF THE OUTSIDE AREAS. CAN YOU RECOMMEND A PARTICULAR COMMERCIAL RUST SOLVENT FOR USE (THE METAL LOOKS GALVANIZED TO ME)?

JOHN WALKER
- LEESBURG, Virginia
^


2005

A. There are a number of commercially available solvents for rust, it sounds like you are only dealing with surface rust so you aren't going to have to use a horribly powerful remover. I'm going to suggest something that Goran Budija has mentioned a few times (he posts on here now and again) "5% citric acid solution (or 50 gm citric acid/1 lit water/+ some ammonia, pH must be 3,5)" A much more environmentally friendly solution, you can get powdered citric acid at many natural food stores, if you have heavier rust you can make it a bit more powerful (double the amount of citric acid in the solution and you have a 10% solution)

Anywho, if you want an industrial cleaner stop by whatever hardware store is nearby, tell them you need a rust remover and see what they have (most of the time I need to derust something I end up using an aggressive acid mixture, I don't suggest it unless you have the cleanup gear for it).

As for the paint? Rustoleum has high-temp paint for outdoor barbecue grills, it's robust, waterproof, and stands up to reasonably high temperatures. And as another bonus, it's spray paint (for those hard to reach areas). Let me know if you need anything else I'll be lurking around here.

Marc Banks
- Elizabeth City, North Carolina
^

Citric Acid 1 lb bag

Affiliate Link
(finishing.com earns a commission on whatever you buy after clicking)



Rust-Oleum High Heat

Affiliate Link
(finishing.com earns a commission on whatever you buy after clicking)



April 16, 2015

Q. I also have rust in my ducts. They are in a slab floor. One of the ducts has a visible hole. I have heard of a plastic coating for this. What is it and how effective is it?

P Madison
- BROKEN ARROW Oklahoma USA
^


May 6, 2015

A. P Madison,
Mastic is a sealing putty commonly used in the HVAC industry. If the holes are very small, just apply mastic and let it dry. If the holes are very large you could attach a fiberglass mesh across each hole and then float mastic over the mesh. You can also use mastic tape.

blake kneedler
Blake Kneedler
Feather Hollow Eng. - Stockton, California
^

help wanted ad
Mfg Engineer - Chem Engineer [Santa Rosa CA]
Plating Shop Manager [Salisbury MD]
Junior Quality Engineer [Santa Clara CA]
Plating Process Engineer [Wenatchee WA]

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

 
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g, Train'g
& Software


About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA