Treating surface rust properly for maximum container life span
Warning- Do not get acid on skin or in your eyes. Most of the products we recommend here are unhealthy to breathe. Always use a properly working double respirator made for organic vapors, and professional grade particle mask when grinding. Thank you!
Step one- Get a small, light weight, high rpm (12,000 minimum) grinder- 4.5” is a recommended diameter, but any size will work. We recommend the bosch 7.2 amp grinder available at gaspro, it is the cadillac of grinders, and only costs $78. You can use the ¼” thick metal grinding discs or the thin cutting discs to grind off the thicker rusted areas. Large, heavy grinders will wear you out quick, they buck too easily, do not spin fast enough and are not at all recommended. Grind off the rust that is flaking on the surface down until you hit metal. Don’t worry about grinding every tiny rust vein inside the metal, just get everything off until you get to bare metal with little veins of rust inside the metal, and do that everywhere on the container. Do step two as soon as possible, don’t leave bare metal unprotected for more than 12 hours. If you want to avoid step 2 (acid treatment) all together, you can apply two coats of rust bullet on just the rusted spots, not on entire container. Rust bullet is rated number one by the US Navy to seal off the elements from the metal. It is super expensive, but our extensive use of the product shows us that it does in fact work. Once that cures for a few days, you prime and paint with industrial oil based paint.
Step two- Apply the zinc phosphate acid treatment made by the EZ clean company called etch and prep, available at home depot for about $15/gallon as directed, apply liberally onto the grinded metal and let it sit for 4 or more hours. A pressure washer is the best if you can get one to blast off the rust in those deeper veins that the acid has eaten. I usually do 2-3 acid treatments on the rust, washing with a pressure sprayer after each application. This is easier than grinding into those veins forever with the grinder. Another good alternative to this is to apply rust destroyer onto those grinded spots. It is an oil based rust converter. We use it all the time when building our mobile container offices as it saves a lot of time compared to the acid treatments as desc above. On big island, HPM has it. They carry a lot of really high quality products and come highly recommended. They also sell the best patch for holes in metal. Its a 1/4” thick bitumin rubber roll that you cut out and stick onto the area you want to patch. It has aluminum on the the top and will not come off. It sticks superbly! Sometimes we apply the patch, caulk the edges of the patch w PU caulking and then put a super thick coat of rustoleum or similar paint. That patch is good for at least a few years if done as desc. Ok, continuing from above- When you have eaten down to bare metal as best as you want to do, wash the entire container with industrial grade liquid detergent and a large, abrasive green scrubby cloth. We recommend using a drywall sanding swivel pad and pole and attaching two large green scrubby cloths that are sewn together to the large rectangular swiveling pad. This is because they don’t seem to make a green scrubby long enough to reach across the swivel pad. The swivel pole pad fits inside the corrugated metal surfaces of the container really well. Doing this on your hands and knees is not fun!
From this point, you have two processes to choose from- doing it well or doing it exceptionally well. I will start with doing it well:
How to do it exceptionally well
Option 1- Apply two coats of rust bullet on just the rusted spots, not on entire container. Rust bullet is rated number one by the US Navy to seal off the elements from the metal. It is super expensive, but our extensive use of the product shows us that it does in fact work. Once that cures for a few days, you prime and paint with industrial oil based paint.
Once container is totally dry after the washing, apply one coat of the rust destroyer/rust converter only on the grinded metal areas with a brush (not on entire container) and apply a second coat 20 minutes later approx. Two coats is essential! You cannot spray it, and a roller is wasteful, so use a large brush for big areas. Do not apply second coat earlier or much later. Once all grinded areas have 2 coats, let cure 24 hours or whatever the can says (I believe 24 hrs is right). You need to wear a good double respirator as the fumes are horrendous. Once you open a can, you need to use the whole can fairly quickly as it doesn’t store very long. I pour it into multiple smaller mason jars and use 1 entire mason jar in one sitting. Be sure to not have much air in the mason jars, and cap tightly right away. I have successfully stored it that way for several months. Air exposure will cause the product to get thick and set-up really quickly. Rust bullet is by far the best rust smothering product on the planet, but rust destroyer is an excellent 2nd choice.
Heat-reflective & waterproofing coatings are recommended
Silicone elastomeric coatings are the best for protecting your roof from ponding water and the rust that results from that ponding water. We like GE enduris as it does not require a primer, and it is an excellent product. If you cant get that product, the old GACO formula sticks without a primer, but it gets dirty quickly, so I would go out of my way to get the GE. Silicone is not rated for catchment, so you can use a heat reflecting paint called NXT cool coat if you are catching water off your roof. We get ours at the cool roof store in honolulu. They will ship it to you at a reasonable cost. Call them for details- 808-591-1900. That paint is excellent to reflect heat off of container walls. There is no other product like it. In the past we have used silicone on walls, but it gets a bit dirty, and its a bit gummy feeling and does not render a nice sprayed finish, so now we use the NXT and like it.
Always keep containers off the ground. Moisture wicks up from the ground, from a concrete slab and also on blacktop. We use 16” X 16” X 5” thick blocks from Home Depot, they cost about $10 each. Unfortunately, it is much too much trouble to treat underneath the container floor, but if you’re off ground, container floors rarely rust out completely unless you are right on the ocean. If you are concerned, you can put a rust-proofing compound from Sealmaster called Flexmaster over the rusted areas underneath to help starve the rust from air and moisture. This product is quite effective, and the cost is very reasonable.
To conclude- it is so much easier and cheaper to work with a new or premium grade container. Doing all this rust work and paying for all these expensive paints is not cheap and the labor is not fun. If you pay someone to grind the rust, you will pay a ton of money, so be smart and buy a new or premium grade container and all you will need to do is keep it painted every 4-5 years or as needed. We do recommend silicone elastomeric coating applied on the roof of any container to prevent rust from ponding water. The floor on a new container is not rusty, it has fresh undercoating, so you do not have to worry about your structure crumbling after all the money you spend building it out. On our used premium grade containers, the steel floor components are generally less rusty, and you can apply rustproofing materials such as flexMaster, made by Seal Master, or similar for a satisfactory result. Insulation inside is good, but not without reflecting as much of the sun's heat from the outside as possible. A metal container structure behaves like a wood home with elastomeric coatings applied to the roof and NXT paint on the walls. Metal conducts heat aggressively, but we have great solutions to these problems, and you end up with a solid, comfortable living space that will last forever if maintained as desc on this page.