Weld thru primer

[Bobo]

Hi all

what does everyone think on this stuff?

As it says in the ad, water based and lloyds atributed.

Surely if its lloyds have put their name to it, it must work.



http://www.lb-restoration.co.uk/cgi...d=1291481520.7456&product=RESTORATION&pid=493

Im not sure if the links working, I cant get it to.
Try copying it into your browser separately in a new
tab or window, it worked for me then.

 

[Chickenjohn]

I wouldn't want to be putting ANY water based product on bare metal! which a weld thru primer will be used on. Water on bare metal = rust which the weld thru product is supposed to prevent. Just buy a weld thru solvent based zinc spray such as the 3m one or one from screwfix/ toolstation of Frost.

 

[TechnicAl]

It works as a primer but weld-through depends on the thickness. Unless its sprayed on very accurately to a very precise thickness it causes porous welds. I recall one shipyard where if it was 17 microns it was OK but at 20 microns you got porous welds. Also the thicker it is the better it works as a primer.
Therefore its best to linish it off in the region to be welded but you dont have to be over cautious like you would with normal primers.

 

[Welderpaul]

We buy all structural sections in blasted and primed. Its just a holding primer to stop it flash rusting. As Technical says, if its too thick you get the odd porous weld. For critical joints we tend to grind it off. A lot of the big sections are blasted and sprayed on automatic lines so control of primer thickness is usually pretty good, plus they are always trying to limit the amount of paint they use.
It always gets a good couple of coats of two pack paint after fabrication so as long as the primer bonds correctly to the steel and the top coat bonds to the primer there isnt usually any problems.
Never had any problems with water based primers on blasted steel. It tends to rust if left outside for any length of time as the primer is usually around 25 microns which doesnt last long anyway!

 

[Bobo]

Thanks guys.

I want to use it in between lapjoints and seams on my mk1 escort during building. I did some major work on it 20yrs ago and Im now having to start again with it.

When I took some of the old joints apart that I did 20yrs ago I suppose I was surprised or not maybe, at the amount or corrosion that had developed between things that I did then. They were really just put together with nothing between them but clean metal as all the weld through primers never really seemed to be getting developed until just after I'd finished the majority of the work last time round.

Ive never really liked the thought of some of the solvent based weld thru's due to the fumes that they emit when being welded and from reading some of the things on here about metal poisoining due to fumes. Also the fact that they can often seem to muck your welds up too, unless your clean it right off to start with which I see as bit of a pointless excercise in applying in the first place anyway then.

What does 17-20 Microns account to anyway, am I right in thinking there's 100 microns to the millimetre, or is it a 1000?

As its only between joints due you think I'd get this by brushing it on?
Thanks again guys.

 

[Chickenjohn]

You spray the solvent based weld thru primer on the areas that will be trapped in the overlap and scrape off the areas to be plug welded. That way you will get minimal fumes and when welding you get harmful fumes anyway, so ALWAYS work with a mask or well ventilated workshop.

The advice above seems to be to do with heavy structural work and not 1mm steel as found on car bodywork. I agree though, use a wire brush , sandpaper or scrape off the primer where your welds are going to be and leave the zinc in the overlap.

Best to minimise overlaps anyway on a car restoration- butt weld wherever possible.

BTW, I have been using solvent based weld thru primers with no problems whatsover, so don't panic! Again, do not use water based products in the overlaps in your car restoration, this will encourage rust. The water based primer looks as though it is really meant for heavy gauge industrial use.