I have had a recent surge of people requesting a vast amount of information about difficult High Heat applications. Hopefully this short blog post sheds some light on its difficulties and the products we have to offer in relation to these difficulties, a few things I have learnt through a lot of your queries.
When applying to a metal that will have high heat exposure, the first challenge is to remember is that with the metal will expand and contract as the metal heats up and cools down. You need a relatively flexible paint to handle this – so more rigid paints with a scuff protection (polyurethane content) are usually a tough find for these sorts of applications. If the application needs to be abrasion resistant, you may be looking at more regular maintenance.
Applications onto surfaces above room temperature are almost impossible. So if you’re factory piping or any application doesn’t allow for the application surface to be cooled and allowed time for the applied paint to cure, you might have some difficulty. Paint is made up of solids (the pigments and resins that give colour, paint properties and bind to your surface) and solvents (the medium in which the solids are dispersed and paint is spread – so water, thinners, turps etc – often said as a “water / solvent base”). After application, the solvents evaporate off the surface into the atmosphere and the solids are what is left behind (ie the larger the content of solids, the greater the quality of paint as more is left on your surface). So, as the paint is applied, over time the solvents evaporate and allow the paint to cure. Applying onto a surface of excessive heat will cause this process to be accelerated; the solvents will simply vaporise and the solids will not adhere and cure correctly.
Having rust on your high heat application is also a bit of a difficult aspect to address. Direct to Rust paints like Oxirite have an inbuilt rust curing chemicals which adds to the rigidity of the paint. So as mentioned in paragraph one, this can be a boggy with the expansion and contraction aspect of the task. Oxirite can withstand a continuous exposure of up to 80 degrees c once cured and intermittent exposure as high as 150 degrees c. once cured; this is not going to do the trick for braais, chimney shoots etc. You need a high heat paint like Xylazel High Heat Paint which can withstand and exist in temperatures up to 600 degrees Celsius.
Be careful to avoid putting a rust curer/ converter on the rusty bits and overcoat with an high heat enamel. Unfortunately, by applying the rust curer, you effectively put on a base coat (which may or may not be able to endure high heat), and as the metal expands and contracts, the base coat is likely to crack and cause premature flaking of the top coat. SO… what is the solution? The truth is, I have not come across a long term DIY solution for this at this point. There are obviously complicated industrial solutions for these high heat problems in refineries, steel works etc that are not accessible to you and me.
Xylazel Metal’s High Heat Paint will adhere well to cleaned off rust (the best possible scenario is getting it back to the metal), while it isn’t going to contribute to the curing rust it has inbuilt rust inhibitors which and will create an effective barrier between the metal and atmosphere which slows the rust formation process immensely. If you use any of the high heat solutions on the market directly onto a rusted surface, regular maintenance depending on the sort of corrosive conditions you live in, will be imperative in ensuring you curb the rust from spreading further. We recommend over-coating Xylazel High Heat we recommend every 18 months in rust application circumstances at the coast, and this is probably going to be one of the better performing products out there. You could also use a coastcote metal primer like SNK 1 or similar if you prefer a primer-top coat application method.
The last aspect of frustration is how high can the temperature be? There are a number of packaging standards around the world that differ and can be misleading and confusing. Take for instance, in South Africa, the highest torched heat (intermittent heat exposure) the paint can withstand needs to be quoted on the tin. In Europe and The States, the highest temperature the paint can exist in cannot be over stated etc. South African manufactured products will often have temperatures on their tins exceeding those of EU and US products because of these regulatory differences. Be sure to identify the use of the product and the conditions it needs to be able to withstand; and then, before launching into purchasing a product, make sure the quoted heat resistance is aligned to your needs.
Any more questions – please shoot them our way.