Topcoating POR-15

[Ferrino]

I will be taking my fuel tank back to bare metal and was thinking of using POR-15 followed by undercoating (Wurth underseal from our host). What is the best way to prep the POR-15 surface for a topcoat like Wurth underseal? Some say to scuff the POR-15, some say use their "tie-coat" primer, others their "self-etching" primer... Would a generic self-etching primer aerosol be OK? I'm keen to find a tried and tested method because it would be miserable to have to redo the topcoat. Cheers!

[scottb]

In my experience, POR-15 has pretty good tech support. You might just give them a call and find out what they think will work best with their product. Undoubtedly they will recommend their own primer, but at least they can give you the technical reasons for doing so.

[Reiver]

You need some kind of technique other than applying over the dried/hard POR 15 as it has such a slick finish whatever will eventually peel off (might take a year or so but it will).
I've scuffed it up, so it has some tooth, with good results .
Never used the 'proper' products.

[dtw]

Spray the undercoating while the POR 15 is still tacky from spraying it. I have done this many times including half a car unibody and a gas tank both with undercoat. Zero issues over 10 years out.

[creaturecat]

love that POR 15.

[Bob Kontak]

Originally Posted by Reiver

I've scuffed it up, so it has some tooth, with good results

Agree. You need to create mechanical adhesion ("tooth") or you are pissing in the wind.

If tie-coat primer or self etching primer creates tooth, great. But if I did not know for sure, I would scuff it with 120 grit, then put the primer on. POR-15 is like glass and is just about as hard.

Give yourself a fighting chance and beat it up first - thoroughly.

FWIW - I know a tool crib guy at a machine shop. He has cars but no real experience in car painting or finishes. I was about to buy POR-15 for the first time and I asked him about it. First thing he says is "Make sure you scuff it up or no second coat will stick". They base coat machines when they rework them with POR-15 then over coat with green or gray.

[Bob Kontak]

Originally Posted by dtw

Spray the undercoating while the POR 15 is still tacky from spraying it. I have done this many times including half a car unibody and a gas tank both with undercoat. Zero issues over 10 years out.

Never thought of that. Sort of a wet on wet application. Must create a chemical bite.

[Reiver]

That is a factory recommendation, top coating when tacky. Tacky as in drag your finger nail over it and it gets a 'bite'.
My problem is in the dry SW it takes so long to dry (moisture helps it dry quicker) that you can wait for hours to apply whatever....easier for me to rough it up the next day.

[GaryR]

Why not simply Epoxy prime it and put a good coat of the Wurth stone guard on it? Looks factory and is VERY tough!

[Ferrino]

Originally Posted by GaryR

Why not simply Epoxy prime it and put a good coat of the Wurth stone guard on it? Looks factory and is VERY tough!

I don't have the appropriate compressor/spray-gun setup. Although I have seen there are aerosol 2-part paints now...

[mreid]

Dude, buy a Preval sprayer, mix up epoxy primer, spray and toss the sprayer. Problem solved!

[drcoastline]

I used SEM Rust Shield mixed 8/1 with hardener on my tank and tub. I sprayed it through a cheap HF HVLP touch up gun. When the time comes I will scuff with a 3M red pad and top coat with Upol Gravitex. I wanted Wurth SKS but the original product isn't available any longer.

[MTemp]

Why not just use the POR-15 Tie Coat primer????

Made for the job, by the makers of POR-15

TIE-COAT PRIMER

Then any product you want to create the fuel tank finish. I used 3M seam sealer in a bag. Only problem is it uses a special gun to apply, but it gives a perfect factory finish. You can then paint it if you want to any colour you fancy.

You can even 2-pack on top if you want…..

Mick