Creating Oxalic Acid Gel for rust removal

While this question relates to an automotive application I consider that it is liable to be best asked on this site.


Summary:


* I wish to create a low cost gel suitable for mixing with Oxalic acid to produce a material that was adequately thixotropic to remain on the underside of horizontal metal surfaces in a thin layer for maybe an hour.  

Longer would be good.
* It would be a significant bonus if it also was suitable for use with phosphoric acid.




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I'm investigating various means of automotive chemical rust-conversion and rust-removal.  

There are many weird and wonderful DIY solutions (potatoes actually do work ! :-) ) but the two that seem most worthwhile are


* Phosphoric acid as a rust converter.  

This is a very common and well respected means of converting rust to insoluble and stable iron-phosphate.  

Concentrations in the order of 25-50% seem typical.
* Oxalic acid as a rust remover.  

This seems to be slightly less well known but is a technically sound method of converting rust to water soluble iron-oxalate which can then be removed by hosing or waterblasting.  

Supplied as a water soluble powder mixed with maybe 3 to 10 parts by volume with water (may have much more water).


I have tried a commercial rust removal gel whose formula is intractably secret (I tried) but which works superbly to convert serious rust to a soluble state which could easily be removed with a waterblaster. The product is excessively costly for the area that I wish to deal with.


Oxalic acid (solid powder dissolved in water to suit) also works well BUT, as it is about as viscous as water, has the nasty habit of dripping off rather than remaining on the surface for the desired periods of tens of minutes or more. Especially so on vehicle undersides :-).


I would like to produce an Oxalic acid gel carrier to solve the above requirement. Ideas encountered for possibly suitable gels include agar, gelatin, cornstarch & vinegar, seed based gels - with boiled rice "porridge" a likely candidate, and more.


I'd be interested in knowing if anyome else has experience in either DIY gels or other products that might allow me to formulate a suitably thixotropic rust remover.


