2011+ frame rust query

I have a 2011 TRD Tacoma , I took it to the dealer because I noticed rust on the skid plate and frame welds. It was surface rust but I paid to get it rust proofed/ undercoated (7 year warranty) when I bought it . They told me it wasn't bad enough to address so I asked them how bad it would have to be before they would address it. They told me it would have to totally penetrate the frame. So I had them document it and went to Walmart and bought some rust converter and put it on the skid plate , frame rails and front end components.It turned the surface black.That was a year ago and the rust has not come back . If you use it use the brush on not the stuff in a spray can.
Good Luck..

 

Rust converters (RCs) can work well, however it is important to understand they are not rust preventative, corrosion resistant coatings (CRCs). They work by using an organic acid (often tannic acid) to literally convert iron oxide (rust) to some stable compound--iron tannate if tannic acid is the active ingredient.

What should be obvious, but is not "in-your-face" obvious, is that there must be some rust for it to convert, so when prepping the surface you should remove any heavy or flaking rust, dirt, oil, etc. but do not remove any firmly bonded rust. This is the stuff that will be converted, if you remove it there will be nothing to convert.

RCs also include an organic polymer that cures to provide a protective primer layer and can be repainted or coated with your favourite CRC--however this polymer primer will not prevent future rusting beyond the life of the primer. Same goes for using it on bare metal, as stated above rust converters are not CRCs.

This is from the Loctite Extend technical data sheet:



Here's a link to the Extend MSDS, Loctite lists organic acid (proprietary) as an ingredient; this is most likely tannic acid with something added to make it "proprietary"...