Repairing chassis box sections - paint inside surface first ?

[v8burbling]

Hi all,
As title really. I have previously repaired an A-post with a repair panel and it rusted through fom inside out (not near the seam) within a couple of years. I had primed the inside and then painted with a waxoil underseal first. Probably a bad idea as I think the waxoil caught fire a bit inside when I was welding - not trying that again.

So now I'm doing main chassis rail repairs, what do you guys do to protect the inside face ?
Do you paint before hand with something like Bilt Hamer Electrox or an etch primer or do you leave bare and then use a cavity wax afterwards via a drilled hole somewhere and hope you cover it all ?
I guess even with the etch primer / electrox, the heat from welding blows the paint off anyhow does it?

Same question also for the inside faces of the box section that you have access to before you weld in the repair panel. They are quite heavily rusted. Still strong but it needs something sharpish to prevent/slow corrosion down. Been looking at Dinitrol stuff but that would again need spraying in afterwards to prevent fire risk.

Thanks, Matt

 

[Rig Pig]

I leave it bare and blast it with a shultz gun through a convenient hole, if there isn't one I cut one with a 20 mm hole saw so I can use a closed electric grommet to plug the hole.
I use waxoil thinned with a drop of cellulose thinners so it runs well.

 

[v8burbling]

Thanks Rig,
What the longevity of that protection. Have you had any bits like that for several years that have lasted well ?
Cheers.

 

[v8burbling]

Good idea with the electrical grommets. I had seen Frost were selling plastic plugs but the grommets will give a better seal I expect.

 

[Rig Pig]

The longest lasting job was the sills on my mum's car - still sound 6 years after welding, I think I popped the grommets once and re dosed it. To be honest most of the other jobs I do don't stay around that long as family and friends change cars.

 

[steveo3002]

anything you paint on will get burned and wrinkle up for say 2" either side of the weld

i go with a spray of weld thru primer then lashings of cavity wax through a hole

 

[graffian]

Bare metal, than I drill 20mm holes if necessary and spray hot Dinitrol.
As to longevity I repaired my Land Rover chassis extensivley, that was in 2000 and it's still good.
I have re-Dintroled the inside several times since 2000.

 

[v8burbling]

Hi Graffian,
Is that the 3125 stuff you are spraying in there ?

 

[graffian]

No AV5 or AV50, it was used for painting the engine bays of helicopters!

 

[droopsnoot]

I've put some weld-through primer on the areas near the welds on mine, and something a bit better further in. I think I used POR-15 for the actual box section, and weld-through primer where the two metal faces join. Once I know all the welding is done, I'll pump it full of wax of some kind as well.

 

[anjum]

Weld through primer before welding.
Then epoxy primer as much as I can get into the box section and joints. Then cavity wax such as Dintrol till it drips out. even then I don't trust it!

Graffian, Where do you get the AV5 is it better than the 3125?

 

[graffian]

Graffian, Where do you get the AV5 is it better than the 3125?

I have no idea which is better, AV has a slightly gluey feel to it, and a bit of a solvent smell. It's certainly different to Waxoyl.
As to where you get it? I know someone who paints helicopters, when the company moved he gave me 48 cans of dinitrol, that's why I use it!

 

[anjum]

As good a reason as I can think of!!
Hmmm do I know any helicopter pilots?........

 

[v8burbling]

Can't seem to find AV5. I have been comparing Dinitrol 3125 and Bilt Hamber Dynax S50. They both seem good.