Spraying top coat over POR 15

[Robster]

Hi, I am tidying the rear trunk on my 914. Damp has got under the paint so some rust spots but not bad enough to need any replacement panel. POR15 looks like the best way to tidy it up, but have seen mixed reviews on putting a top coat over it. Does anyone have any experience of doing this? I am going to take back to bare metal, coat it and then get a professional to do the top coat. Any advice or alternative greatly appreciated.

[Northy]

In my experience epoxy mastic is better. The one on rust.co.uk

I found por15 can just peel off if the metal is too smooth. Probably fine straight onto the rust though.

[Nige]

What Northy says, POR15 just seems to form a peelable skin over the metal.

[sladey]

+1 for epoxy mastic from rustbusters

[Robster]

Thanks to all for the quick replies, have just checked it out and looks to be just the ticket. Very much appreciated. Would you recommend using the Fe 123 rust neutraliser first or will the epoxy mastic do the job straight on? I would like to get a good finish with the top coat, so can epoxy mastic be sanded to ensure a quality finish?

[sladey]

Phone rustbusters and ask their advice - they know their stuff. The fe123 is good stuff though - hard to believe it's water soluble

[Nige]

Loctite 7503 rust remedy is very good and has been recommended to me by a few professional types. I then zinc prime with a very high zinc content primer. If it's visible exterior paint finish I wouldn't bother with mastic unless it's chassis under arches areas.

[smallspeed]

I've used epoxy mastic, then a top-coat in my engine bay - I rollered on a thin coat first as recommended by the manufacturer (I brought it direct via ebay), then a second thicker coat with a brush
The problem i found is its quite sticky, so if you use a foam roller it will fall apart! if you use a wool roller it will give a bit of a stippled finish. The brush-coat was a lot smoother (possibly also because it was thicker) however don't buy a cheap brush! I did and (despite pulling any loose ones out first) I spent quite a while picking errand hairs out of the paint

Once its gone off (2-3 days) its quite easily sandable to a smooth finish and makes a great "under coat"
If you're sanding a larger area, or in a confined space, use a mask - its very dusty when you get into sanding it! Also don't wear a dark woolly jumper like I did, as you'll end up looking like an Elizabethan ghost

Some pics:
First thin coat done with a roller (which came out quite glossy)



Second thicker brushed coat (which came out more matt finish)



Sprayed on a guide coat



Half way through sanding



After paint

[Nige]

You can spray it on if you have the gear.

[smallspeed]

if you mean epoxy mastic you'd need a serious nozzle - its really thick and quite sticky, plus im not sure thinning it out would help much.. its got like a filler material or something suspended in it!

[Nige]

The stuff from rust.co.uk gives details on how to thin for spraying, never bothered myself as it's usually chassis stuff that I tend to stipple on with a brush for a textured effect.
http://www.rust.co.uk/rusty-s-tips-how- ... ic/c32749/

[smallspeed]

blimey, I bet that's a messy old job spraying it

It is really good stuff - sticks like s**t to a blanket.. I still have a big splodge on the floor in my garage which has stood up to 2 or 3 years abuse, where the "diamond hard" garage floor paint lasted 5mins
Did the whole underneath and through the transmission tunnel of my 3-series after I stripped everything and dug out all the seam sealer to weld it. I think its really good at sealing up things again, and it really does stand up to some abuse - I had all on trying to grind a small patch off to weld a few bits and bobs on!

[Nige]

Bare metal your engine bay?

[smallspeed]

nope.. bear metalled the seams where I was welding, the rest of it I just sanded down with a pretty rough grade, and its gone on really well
I think it goes on best to bare metal but it works fine on roughed up surfaces - think I went 180grit but it was a while ago..

[Robster]

Excellent info, many thanks to all. I will embarrass myself with a before and after photo once I have got it sorted.