hot dip galv on used chassis - good idea or not?

[julianf]

Sometimes I see used chassis that have been dipped.

How does this work? I mean, how can the internals be properly cleaned up before dipping?

I kind of expect people to blast the outside, then acid dip, and metal dip, and forget about all the junk that must be sitting inside.

Has anyone here confidently done one, and what method did you use? And did you look at the job with an endoscope afterward?

 

[rtbcomp]

My concerns exactly - I'd wax the inside of a new galvanised chassis.

 

[RIP]

Hey I considered this. You're right that the zinc won't stick to the inside of a blasted chassis, so you're just coating the outside. I'm not convinced by the chemical stripping, where the car/chassis is dipped in caustic to remove paint, then acid to remove rust, I do it at home on smaller scale but using the same chemicals and it leaves smut behind and the paint still needs a lot of agitation to remove, it doesn't just disappear like people think. The stripping plants pressure wash the outside to agitate the paint off, but nothing for the inside. Basically the end result is NOT clean bare metal like people think and I don't think zinc or e-coating would stick to the inside which hasn't been done with the pressure washer.

That said, having just blasted and painted a chassis, it is a heck of a lot of work and time, you need five coats (three primer + 2 top coat) plus each coat takes two goes because you need to flip the chassis each time, it takes ages. So I would consider hot dip next time to save work. So blast the chassis, hot dip, and then wax the inside. And the cost of all that paint would offset the cost of hot dip.

Also paint won't get behind brackets and into crevices that sand blasting would have cleaned, zinc/hot dip will.

So the only down side of hot dip is the risk of the chassis warping. This is due to the heat releasing the stresses in the chassis. I don't know how serious this problem is.

 

[RIP]

I read once that some stripping plants use heat to remove paint. But never found info on this, maybe it's better than the caustic/acid process.

 

[Wightsparks]

I am coming at this from a marine angle but isn't the zinc on one side of the metal sacrificial so the inside would not rust? Someone on here will know!

 

[8ob]

I have had a fair few things galvanised , used chassis`s have always gone into the plant as is complete with paint and rust, the only thing they cant cope with is grease so I have always steamed cleaned them. What the chemical cleaning cant cope with the heat from the dip sorts out, I have seen one of my chassis`s strung up and heading for the galv dip and paint was still clearly visible. My advice is don't worry about it, everything I have ever sent down has come back perfect irrespective of paint and rust. I had to cut a small window into one section of chassis I had done to fit some tube spacers and the inside was as good as the outside.

Bob

 

[RIP]

I have had a fair few things galvanised , used chassis`s have always gone into the plant as is complete with paint and rust, the only thing they cant cope with is grease so I have always steamed cleaned them. What the chemical cleaning cant cope with the heat from the dip sorts out, I have seen one of my chassis`s strung up and heading for the galv dip and paint was still clearly visible. My advice is don't worry about it, everything I have ever sent down has come back perfect irrespective of paint and rust. I had to cut a small window into one section of chassis I had done to fit some tube spacers and the inside was as good as the outside.

Bob

Hey Bob. The thing is that although you can see the zinc having taken to the unstripped chassis, you don't know how well it's taken and how it will look after 5, 10 or 20 years of daily use or how it would compare to a chassis that was properly stripped. Manufacturers guidelines (or textbook guidelines in this case as there's no manufacturer involved) are based on lab testing (we hope). If I galvanise a chassis then I want 10 to 20 years out of it. If the guidelines are not followed then the coating is compromised and might not last. I paid £120 to get my chassis blasted, small price to pay to get a guaranteed by-the-book result.

I am coming at this from a marine angle but isn't the zinc on one side of the metal sacrificial so the inside would not rust? Someone on here will know!

I read on finishing.com that zinc (hot dipped or electro plated) will stop rust upto 5mm away. I heard that in the marine world the distance is far more, I assumed this is because a hull is submerged so there's more distance for the zinc to attract the rust causing ions.

 

[8ob]

@rcx132 . I am not saying don't blast it what I am saying is all they asked of me is that its clean, they derust/dip the thing and do the job. Blasting the outside does not clean the inside and both are important. I rebuilt a series two landrover thirty years ago, done the normal chassis repairs like outriggers,rear crossmember etc and sent it off clean but as is for galvanising. I sold it to a friend about fifteen years ago and he still pops in with it so I will take some snaps of it, its still mint. Send in a piece of rusty box section with the ends welded up and some fill/drainholes in it as a test piece, cut it up when it gets back and I am sure you will be impressed.There is way too much misinformation on the web, its really a simple operation.

Bob

 

[RIP]

@rcx132 . I am not saying don't blast it what I am saying is all they asked of me is that its clean, they derust/dip the thing and do the job. Blasting the outside does not clean the inside and both are important. I rebuilt a series two landrover thirty years ago, done the normal chassis repairs like outriggers,rear crossmember etc and sent it off clean but as is for galvanising. I sold it to a friend about fifteen years ago and he still pops in with it so I will take some snaps of it, its still mint. Send in a piece of rusty box section with the ends welded up and some fill/drainholes in it as a test piece, cut it up when it gets back and I am sure you will be impressed.There is way too much misinformation on the web, its really a simple operation.

Bob

Fair enough.

The rust removal that they do before hot dip is only designed to remove scale and light rusting though. Deep rust takes days to remove with acid, and again, agitation.

 

[julianf]

I've been repeatedly pressure washing my defender chassis before applying wax.

Every time I do it, more crud comes out. Rust will be eaten by acid, but I'm talking just grime.

I cant think that any non abrasive (be it water pressure, sand, etc) will remove solids, and, further, I can't see any process actually removing it all?

 

[Rannsachair]

My recent experience with a Defender chassis was that it looked fine after blasting and came back from the galvanising with some holes, their cleaning and hot dipping certainly removed more than surface rust. The internal sections of the chassis that can be seen are well coated. Costly for me as ended up buying a new galvanised chassis, that I am just about to wax internally.

 

[8ob]

Still to much overthinking going on Rust cant continue without air and moisture, the temperature involved in this process is huge and any moisture is driven out of every nook and cranny. Galvanising will then coat/seal in all the multilayers of steel inside/outside of the chassis sections ( of which there are many) even if its pitted or there are flaky bits of steel in there, the whole lot gets covered. There is no other process that can achieve this with the same long lasting results. Do all your repairs,clean it, stick it on a trailer, take a cordless drill, go down to your nearest galv company, get the foreman out, explain to him you don't want it coming back like a banana , ask him where he would like the drilling's, explain there will be no extras.Job done and you will enjoy a rust free chassis for many years to come

Bob