What on earth did I do wrong?
Posted by Toby-pearse@reddit | projectcar | View on Reddit | 30 comments
What on earth did I do wrong?
I removed the factory sound deadening from my ute as it had gone all gross. I had scraped some paint off whilst doing it so I figured I'd repaint the floor. I wire brushed those sections to bare metal. After that, I cleaned everything thoroughly with wax and grease remover, then coated it with a rattle can of epoxy primer. I then applied car builders sound deadening over the top and honestly thought I’d done a solid job.
A few months later (today) I decided to redo a section of the sound deadening because it looked a bit messy. When I pulled it up, I found what looked like pitted rust underneath the primer. After scratching around a bit more, I learnt the whole floor was getting rusty under it. The floor was completely rust free before hand, so now I feel shit because I've basically spent time and money making everything worse...
Im going to rip it all up and start over but I need help understanding what the hell went wrong and what I should have done instead/what products I need to use now. Thanks.
JCDU@reddit
If there's rust you need to neutralise it with phosphoric acid or similar products not just brush away the evidence.
Primer is porous - it's designed to be so that paint sticks to it. If you don't seal it with some sort of top coat it's going to let moisture through and corrosion will come back.
Toby-pearse@reddit (OP)
Right. Best answer so far, Thanks. I figured if you pulvarise surface rust with a wire brush it's gone lol. The can said "non porus" but that kinda contradicts what primer is.
pilot64d@reddit
This is 30% phosphoric acid. You can get it at lowes, buy a spray bottle, and apply.
Strip the paint back to bare metal first.
Here's the SDS
Doctormentor@reddit
Wet paper towels and keep em soaked for time required, I'm just guessing. Works when I bleach my shower walls. Wet the papertowels with bleach and keep. Coming back making sure it didn't dry yet... In your case rust stuff. Or just keep brushing it on to keep it wet for time it says
JCDU@reddit
There's a hundred rust-fixing potions out there, most of them will do very similar jobs just follow the instructions on the bottle.
I like Dinitrol RC900 but I've used Kurust, Jenolite, Phosphoric Acid, Zep, EvapoRust, NeutraRust, and a few others... the key really is they kill the underlying chemical reaction so when you paint over it it's sealed in and isn't coming back.
Others I've been recommended are Bilt Hamber, Oxalic acid, Ardrox 1218.
Using a zinc-rich primer is important too IMHO, there's a lot of different primers aimed at different purposes (EG filling imperfections) but they don't contain anything to discourage corrosion.
I've also used ACF50 which is a fairly light corrosion inhibitor spray for small tight areas, and I tend to use Dinitrol waxes for chassis & body cavities.
minorthreat999@reddit
The floor was in fact NOT rust free before you painted. It may have appeared so.
Toby-pearse@reddit (OP)
It was infact rust free. I was the one who scratched the paint off in the first place when I removed the factory sound deadening. Every section that I painted has gone rusty, im assuming moisture has gone through the primer and started to rust it out. The rust is only surface at the moment.
SolidVeggies@reddit
How’d you metal prep?
Definitely looks like it wasn’t sealed correctly? What products did you use?
Toby-pearse@reddit (OP)
Wire brushed, vacuumed the dust then used wax and grease remover. I can't remember the exact paint but it was an epoxy primer from my local auto parts store. I guess I'd figured that primer was enough for protection and that a top coat was just to make it look good. I didn't care what it looked like as it wasn't getting covered up.
ryman9000@reddit
You'd have to kill the rust first. Use rust mort on bare metal where their is rust. Wear a respirator because that shit is toxic. Let it sit for 24 hours and then you should "kill it" with water. Yes, water. Water neutralizes the rust mort but then you should wipe off the water and maybe use an air blower to evaporate it faster.
Rust mort turns rust from orangish to black.
So, wire wheel/brush, then rust mort, kill with water, evap water. Primer etc...
Doctormentor@reddit
How do they dry it fast enough to not flash rust. It's like cleaning a cast iron ... I only takes seconds to get that rust on there unless it's covered in oil
ryman9000@reddit
So, I'm no chemist but I when we would restore classics and hot rods that had any rust, we would use something like rust mort and my boss always said to like wipe it with a wet rag after it sat for 24 hours to neutralize the rust mort. And then we would blow it off with a compressed air blower to force evaporate the water so rust wouldn't form. Is it flawless? No probably not. But you've killed all the rust there with the rust mort and have a highly reduced risk of that spreading now and the rust mort is no longer active so it shouldn't mess with the chemicals in the primer. Do you have to neutralize the rust mort? I have no clue. After 24+ hours it usually seemed to be evaporated to me but I just did what the boss told me.
While I worked there, we never had a car return for rust coming back and I never saw any that they worked on before I worked there, show up claiming rust had returned.
minorthreat999@reddit
Not true
anywhereat@reddit
Top coat is a sealer. Primer will retain moisture.
Fun-Tap-8794@reddit
did you wire brush it by hand or with a rotating machine?
wire brush will never ever be able to remove rust. it is only able to remove loose rust particles which would be ok if you use rust converter. But then the rust is only sealed from water and oxygen.
the worst is wire brush on a drill or angle grinder. the rpms are too high and so the rust will appear to be gone but in fact you brushed it into the surface and created a hard surface of rust particles.
you have multiple options:
grind with angle grinder so much that you are sure the rust is gone
chemical rust removal
sandblasting
or laser cleaning.
otherwise you will always have rust
JCDU@reddit
If there's corrosion, even if you wire brush it that's not killing it just removing the evidence - I'd always treat it with phosphoric acid or similar rust killer / passivator / neutraliser etc. before putting anything on top.
minorthreat999@reddit
It was in fact not rust free. It’s obvious
minorthreat999@reddit
I would ospho it if your not replacing metal
theeaglejax@reddit
Zinc chromate aka self etching primer is your friend after getting the corrosion under control.
404-skill_not_found@reddit
Personally, after cleaning, I acid etch all my bare metal as the first step on the way to paint. That and get to the primer shot without delay. Otherwise, exactly what you have experienced is assured.
akep@reddit
You needed a primer sealer, god knows what primer you used and probably got the wrong one.
Toby-pearse@reddit (OP)
"epoxy primer" "non porus" " no topcoat required unless exposed to elements" I just read the buzzwords on the can lol
ONE1-ZERO@reddit
You have to top coat primer. Light scuff and hit it with high build self etching primer. Something like SEM. The $30 cans you get at a paint shop. Not rustoleum. Then top coat it with something with hardener. Tractor paint from TSC reduced and hardener added works. If you don’t want to spray it use a foam roller for cabinets to get it to lay smooth.
Jacklunk@reddit
Lolz. I use Mack truck red primer myself. It has a rust inhibitor. Used it on trucks up here in the northeast and they hold up
ONE1-ZERO@reddit
Also in the northeast. I use the red structural/fabrication primer for welded projects. Never thought about hitting a car with it.
ManLindsay@reddit
But it is exposed to the elements….
Toby-pearse@reddit (OP)
I guess I interpreted that as being outside, I figured inside a car with a layer of sound deadening stuck to it would be fine.
RuinAccomplished6681@reddit
Or a zincspray I guess?
hzewski@reddit
Ouch...the rattlecan epoxy was the biggest issue..not enough thickness in the coating,moisture went trough it.and the moisture does not come away because of the mat🤔plus,only the epoxy in the surface is not enough,you should top it with acrylic or urethane paint,let it dry completely and then assemble with deadening mat.
Fragrant_Lobster_917@reddit
Using primer as the only coat is a big no no. It doesn't do much to keep moisture and debris out, its only good at holding onto stuff.