To dip or not to dip that is the question

[Diecastinvestor]

Hi,

I am in the final stages of stripping my car and always planned to have it soda blasted to remove the paint so I could protect areas like the original chalk numbers on the dash. However I do see a lot of people having cars dipped instead. I have heard stories of the acid/alkali weeping from joints after this has been done and ruining new paint etc. I would appreciate views on what is the best process.

Many thanks

Nick

[RichardBTek]

Dip it. Only way to completely clean all rust from car. and much better to work on. Make sure all seams are dry and sealed before you get it painted and you won't have a problem. You will need to get the whole thing primed straight away though before you start work.
Richard.

[KS]

Go to Enviro-Strip, nobody else...

[Darren65]

Personally I would never dip.....my opinion stems from many a conversation with Barry Carter who knows these shells as well as anyone.

Any dipping or heating process effects areas you just can't get too.....media blasting only imo.

[Northy]

I had a pair of wings dipped and e-coated and had problems with seams rusting at the trailing edge. That was on a easy to get to place and should 100% have been sealed probably - personally, I would not want to dip a whole shell for this reason.

[fetuhoe]

there is always a huge amount of argument about these processes and the devil is always in the detail.

If you Soda Blast it will be virtually impossible to remove underseal and sealants as the Soda just doesn't have enough Kinetic Energy,

If you blast with a more aggressive media there is always the potential to store residual energy in the panels and ripples can develop after the car is driven when the vibrations cause stress relief.

Thermally processing the shell in a controlled pyrolysis oven is a 'safe' technique and doesn't cause any distortion.

These ovens are used to clean the paint and body jigs used by car manufacturers and temperatures are controlled to around 380 degC and shells don't distort at these temperatures.

The issue of dipping is a bit more complex and is done to remove the 'flash' corrosion that occurs when all of the ash that forms on the shell is pressure washed following the thermal treatment.

The first company that used this technique used Hydrochloric Acid dip and this can cause issues as the acid can penetrate seams and will concentrate over time and can then leach out and ruin paint work.

Envirostrip and Prostrip use a Phosphoric Acid dip treatment that creates a passive surface film which is a surface conversion and any residual acid solution left in the seams just creates a slightly thicker passive layer and never leaches out.

Hydrochloric pickling produces a much more active surface to the steel hence the need to prime almost immediately.

[Nick Moss]

I have been getting shells dipped for 15 years (most recently with Envirostrip) with no issues. It's the only way to completely remove all the paint and sealers.

[MikeyC]

Hi,

I am in the final stages of stripping my car and always planned to have it soda blasted to remove the paint so I could protect areas like the original chalk numbers on the dash. However I do see a lot of people having cars dipped instead. I have heard stories of the acid/alkali weeping from joints after this has been done and ruining new paint etc. I would appreciate views on what is the best process.

Many thanks

Nick

Nick, in my mind, the decision on whether to blast or dip depends on how far gone your existing shell is, rather than there being a generic best process. For example, are you planning/needing to cut open your sills and replace your heater tubes? They're made from fibre-mat insulated flexi-tube, so will be destroyed if you dip your shell. They can only be replaced by cutting out the sills. That's a lot of extra work if you don't need to do it.

PS, I like the intention of protecting the factory chalk markings. Structurally they are meaningless, but historically they are important, even if they're invisible on a finished car.

Regards,

Mike.

[fgmec]

https://www.wwtsrl.it/en/restoration-wo ... echnology/

[stretch]

I seem to recall Barry suggesting that the dipping companies should cut open a box section to see if there is any residue or stripped paint present. Put your money where your mouth is, so to speak.

It never ceases to amaze me that nobody ever mentions how the paint debris is removed from the screen pillars or roof gant rail sections. Imagine the pile of mulch in the cavity pictured.

Think of a pile of nitromors stripped paint from a window frame stuck in the hidden sections of your pride and joy. Dipping removes underseal, but it also removes all the factory primer in these hidden box sections. If someone can explain how this debris is removed and then neutralised, i would love to know the procedure.

Blasting for me.

Dave

[DustyM]

Dipping for me. (I also use Envirostrip)

Imagine all that blasting media trapped inside those cavities absorbing moisture over the following years!

Factory primer inside cavities, you've opened enough cars Dave to know that what's in there isn't protecting anything.

Your picture above illustrates the point nicely, how would blasting remove any of that rust?

It is swings and roundabouts, neither method is fool proof, for me though the benefits of dipping out way the downsides, I would much prefer to work on a car that has been dipped than one which was blasted.

[fetuhoe]

https://www.wwtsrl.it/en/restoration-wo ... echnology/

Looks interesting and the results look good but some of the explantions don't seem great and I would like to know more.

Wrought Metals, unlike skin, don't have any 'pores'.

It is true that cast metals may be porous but if this porosity is excessive then the parts would noprmally be scrap.

Car body steels will have been reduced in section from several metres to around 1mm and as most of the porsity in the ingot tends to be caused by a reducing gas they weld up during fabrication.

Modern continuously cast steels start out at around half a metre thick and are normally free from porosity.

I would have thought that the presence of high pressure water (30 000psi?) would cause flash rusting as the water used must be oxygenated so all of the required componets for the formation of hydrated iron oxide exist. I think you need to use ultrahigh pressure to remove paint and this could casue distotion.

If rusting does not occur then the water being used must be inhibited and this surface would most lileky need to be removed before painting.

It is also quite common to mix an abrasive with the water and this may also leave a residue.

Many Soda Blasters also use a media with an added abrasive to try to remove underseal.

The majority of the closed box sections on early 911s are unpainted and when you cut the pillars on a car that has been dipped there is no residue from the process .

[stretch]

We all have our opinion. Most people that champion dipping seem to be in the trade.

[Gary71]

Question for those that favour the envirostrip method: do you leave it as dipped during metal work or have it primed and clean off locally as you weld?

[DustyM]

Question for those that favour the envirostrip method: do you leave it as dipped during metal work or have it primed and clean off locally as you weld?

We tend to collect the shell in bare metal (the inhibitor will keep it clean for a week or so) then mask off the areas that we know need work or will be removed and epoxy prime the rest. An etch primer or regular primer are no good as they are not waterproof and rust can form underneath especially if it turns into a lengthy project that runs through a winter or two.