Couple of welding questions

[parisian62]

G'day all,

Is weld through primer used on both but and lap joins?

Once the patch is welded in...is the correct procedure to...

1. grind/sand/linish back the welds
2. deoxidine the join
3. etch prime
4. brush on seam sealer

The wagon will be spray eventually in 2 pac.

regards
Stewart

[rosco]

Hi Stewart,
as a welder, I'm a fantastic train driver! As a train driver - I get by ok .......

My opinion, and what I do.......... I rub out all paint around any intended weld - just don't like the thought of something getting into a weld.......... this is just me.

I was told by our welding instructor to use a "welders etch" - I have not ever found one........... but will buy the box when I do.............

He spoke of a problem called "dis-similar) metal syndrome - when a "new" piece of metal is fused to an existing one, one piece acts as a cathode - the other as an anode.
I'm going to frighten everyone here, please relax - I don't believe the issue is as bad as it may sound............ I have spoken to a number of paint/body panel experts with the advice if I was "really concerned" I could hand paint the reverse side with "cold gal" this would "electrically" connect the two and remove any prospect of electrolysis............ I have done some jobs with it, some without - too early (only 5 years so far) to tell if there is a problem with the "non-treated" repairs............

To me, your sequence is correct but, I would certainly include some sort of top coat before applying the sealer - especially if it is bituminous......

frats,
Rosco

[munro]

G'day all,

Is weld through primer used on both but and lap joins?

Once the patch is welded in...is the correct procedure to...

1. grind/sand/linish back the welds
2. deoxidine the join
3. etch prime
4. brush on seam sealer

The wagon will be spray eventually in 2 pac.

regards
Stewart

always weld to clean metal
after etch use a paintable sealer ie sicoflex and when you smoth it ova with clean hands dip your finger in some prepsol (wax and grease remover) making sure your finger stays wet.
the reason for this is it preps the sealant for paint and the sealer doesn't stick to your finger giving a smooth finist.
never leave the car in etch only as etch absorbs everything.
undercoat/spray putty the area that was etched.
this will give you a good base.
cheers tom

[parisian62]

thanks your suggestions/responses Munro and Rosco...

Just got off the phone to a PPG rep who works out of Holden at Homebush, Sydney. He has suggested to use the 3M weld through primer both before and after welding. Of course don't let any moisture get to it before painting and it can be wiped off with thinners just prior to final painting.

Once a get a can I'll let you know the part number Rosco if you want to chase a can for yourself...or I'll buy one for you and bring it to Yamba...let me know...

regards
Stewart

[rosco]

Thanks Stewart,
just chasing some up now - looking forward to "road testing" it.....
will report...

frats,
Rosco

[parisian62]

...bought a can of 3M weld thru primer...sitting down?...$40....

regards
Stewart

[Blacky]

How big a tin ????

[parisian62]

standard aerosol can.

[Blacky]

[rosco]

Has to have gold or platinum in it......... guess I won't be buying a "box".

Thanks Stewart,

frats,
Rosco

[munro]

Has to have gold or platinum in it......... guess I won't be buying a "box".

Thanks Stewart,

frats,
Rosco

the box is $50
the cans are extra

[rosco]

If the box is $50 - must have over-filled the cans............

frats,
Rosco

[Errol62]

Old post but been researching weld treatment and thought I would add to what has been said.

Zinc or copper enriched weld through primer is recommended for spot and plug welding seams applied to the mating surfaces. Needs to be cleaned off weld spot when plug welding. The zinc melts in welding and forms a protective surface. Exposed surfaces are then taken back to bare metal, prepared with dioxine, etch primed and promptly covered with primer of spray putty. Etch primer should not be left exposed as it is porous. For butt welding grind, prep, etch and prime.

This is my understanding. It would be very helpful to hear from anyone with an opinion on this.

Cheers
Clay


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[parisian62]

Wow this one is an old post.

Old Timer was sprayed in acrylic...

[rosco]

Hi Clay,
yes - and oldie, Stewart.
I got my info from the chap who taught me to weld at TAFE. He was very concerned that my MIG welding would cause issues under paintwork.
I asked him about using "welder's etch" (UPOL brand) to which he stated that any of them would do... but it had to be part of the weld "pool".
I did wire brush after welding -then primed with a zinc primer ... once that had settled down - I primed again with an enamel primer.. then multiple top coats.
My belief, was that the zinc primer would "seal" whatever was left atop the weld... the enamel primer would then seal that out against becoming absorbic... the top coats, of course seal the entire lot from ingress of moisture and wear/tear...

So far, where I have applied this treatment continues to show not one jot of any lifting or "growth"...

pix - from not long after finishing the cabin side floor with Hadfield hump welded in...





frats,
Rosco