How do I fix this rust spot?

Reply

  #1  
Old 04-06-18, 12:11 PM
Member
Thread Starter
Join Date: Apr 2018
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
How do I fix this rust spot?

I have a rust spot on my roof that I want to fix. Originally I thought it was as simple as sanding down to abre metal, putting primer, then painting and clear coat but oh boy was I wrong? I read some places you need etching primer since it's bare metal, then primer, then paint and clear. Some places say you need to sand to all the way up to like 3000 grit.

So I'm really not sure what to do anymore.

 
Sponsored Links
  #2  
Old 04-06-18, 12:22 PM
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 21,228
Received 264 Votes on 239 Posts
Have you gotten some estimates from a body shop? By the time you buy the paint and materials it's likely to be just as expensive or more to do it yourself.
 
  #3  
Old 04-06-18, 12:25 PM
Member
Thread Starter
Join Date: Apr 2018
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
No I haven't. But I don't see how it's more expensive to DIY myself for something this small.

I just want to know the proper way this should be done.
 
  #4  
Old 04-06-18, 12:54 PM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 46,270
Received 140 Votes on 125 Posts
The proper way would be to sand down to clean metal, prime and paint. You'd also paint the entire roof to insure the new paint will blend. You can use an etching primer but don't have to, the same with rust preventive coatings like OSPHO.

Once the primer is on/dry you'd wet sand with 400 grit before cleaning and applying the finish coat. The only thing you'd use 3000 grit for is to 'buff' out a painted surface.
 
  #5  
Old 04-06-18, 03:02 PM
ukrbyk's Avatar
Member
Join Date: Mar 2010
Location: USA/ Pacific NW
Posts: 3,490
Received 5 Votes on 5 Posts
Well, to do this right, you have to remove windshield and molding strips. Or, you WILL damage them.
Next, you need to take a metal scraper and go underneath the paint edge, as far as scraper goes by hand and light hammer taps.
You'll easily end up with spot about 3-4 times size of what you see.
Then you need to sand that down to bare metal with sander. Rough sand paper. That's why you need to have glass and molding removed, to have some work space.
You need to sand around rusted area perimeter until there is no a single sign of rust, as it spreads underneath the paint.
Then you need to use rust inhibitor, like Marine Jelly or phosphoric acid. Just brush it on. Let it sit for few hrs, brush it on again.
Then you bondo it, sand progressively to about 1200 grit. Prime. 2 coats, letting dry between.
Sand primer. Wet or Dry, 800 grit through 2000
Then you need to find a shop that will do color match. Roofs are tough due to being horizontal. Unless you climb up on ladder to be above it but then regular spray can does not really want to spray well down. Unless you have like airbrush or small compressor and paint gun.

It's not as much about expense, color match paint will cost you 60- 80 bucks premixed with clearcoat and hardener. Sand paper will be around 20-30 bucks.
It's very time taking.
Glass removal will be the major expense. Seriously, don't try this with glass in place as I guarantee you, rust went around the edge and under the glass.
 
  #6  
Old 04-06-18, 03:07 PM
Member
Thread Starter
Join Date: Apr 2018
Location: Canada
Posts: 3
Received 0 Votes on 0 Posts
The proper way would be to sand down to clean metal, prime and paint. You'd also paint the entire roof to insure the new paint will blend. You can use an etching primer but don't have to, the same with rust preventive coatings like OSPHO.

Once the primer is on/dry you'd wet sand with 400 grit before cleaning and applying the finish coat. The only thing you'd use 3000 grit for is to 'buff' out a painted surface.
I'm fine without blending it to 100% exact.

Why do I need to wetsand the primer? Isn't the point of primer to make the paint cling to it?
 
  #7  
Old 04-06-18, 03:31 PM
ukrbyk's Avatar
Member
Join Date: Mar 2010
Location: USA/ Pacific NW
Posts: 3,490
Received 5 Votes on 5 Posts
Paint will cling to it due to primer chemical structure. You have to wt sand it to accomplish nice smooth finish. Or, every primer imperfection will show in paint. As I had it done all and any kinds of cheapo ways - with according results. It only appears to be easy job. Then it'll look like crap and in your face.
There is a proverb: we never have enough time to do things right, but always find time to do them over.
 
  #8  
Old 04-06-18, 09:27 PM
Group Moderator
Join Date: Oct 2004
Location: WI/MN
Posts: 19,369
Received 54 Votes on 51 Posts
We're assuming you want to do a good job. If you want to 1/2-a$$ it, go ahead. Doing a good job is A LOT of work and expense. Your car, your call.
 
  #9  
Old 04-07-18, 02:39 AM
Marq1's Avatar
Member
Join Date: Sep 2016
Location: USA MI
Posts: 4,600
Received 121 Votes on 112 Posts
Considering the size of the rust spot I would assume we have an older car and most likley you are not expecting/antisipating that showroom new look just trying to clean up a rust spot.

All products can be purchased at auto parts store, probably $25 and you will have enough for several more repairs.

100 grit sand paper, rust converter, primer, tape, and a can of matching touch up paint.

Realistically you are not going to remove the windshield so protect the glass with the tape, sand down the spot then use the rust converter to get to the area under the seal, prime and paint.

The repair will be visible, as mentioned you are touching up a spot but it wont look as bad as it does today!
 
  #10  
Old 04-08-18, 08:25 PM
Member
Join Date: Jul 2015
Location: USA
Posts: 49
Received 0 Votes on 0 Posts
This is a challenge because of its position on the roof. I would suggest a POR-15 starter kit. This gives you chemicals for cleaning as well as the POR-15 paint. Then you can go over that with your car paint., but the POR-15 will definitely end the rust. I think you will be able to work around the seal unless you are unlucky. Despite the fact the POR-15 can paint over rust, you should do your best to get all rust off first. This little starter kit will be plenty to do any additional rust spots around or under the car.
But you will need to make an assessment of the rust spot underneath. If the rust has almost certainly penetrated, then the rust must be treated on the back as well as the front. It is no good to leave weakened metal. In that case you must cut out the weak metal and weld in new. You cannot fill a hole with Bondo. It must be welded or backed with something. The bigger the job gets the more it needs a professional.
 

Last edited by richard123vmt; 04-08-18 at 08:57 PM.
  #11  
Old 04-12-18, 05:20 PM
Member
Join Date: Sep 2003
Location: Arlington, VA
Posts: 860
Received 0 Votes on 0 Posts
Given the car itself and the assumption that you're not trying to make it look showroom, you're just trying to prevent more rust from eating away and leaving a hole in the roof, here's what I'd do.

This assumes you have an air compresser, hose, and spraygun. A home depot spray gun is fine as long as it's HVLP and gravity fed.

- Lookup the paint code based on year/make/model

- Get a quart of that paint code at a shop that sells autopaint

- Also get a small quantity off the shelf of the cheapest paint they have for use as practice paint to practice your spraying technique

- The paint store will also sell you reducer and hardener and tell you the mixing ratio. They usually provide free measuring buckets.

- Get a can of lacquer thinner and prepsol

- Get a spraycan of "buildable" primer

- Get a couple scotchbrite pads, green, maroon, and gray

- Tape off the windshield moulding along with the other edges of the roof

- Use a scraper to scrape off the flaking paint

- Use 400 grit on down/coarser until all the rust is gone

- Use the remaining 400 grit to scuff the rest of the roof (you're going to do the whole roof to ensure a matching color and probably it could use a refresh anyway)

- Wipe it down with Prepsol

- Spray the buildable primer evenly across the roof

***When spraying from a can or sprayer start far and work your way closer,
don't stop and turn/instead go all the way off the edge then come back,
and never spend too much time in one area***

- Wait about 20-30 minutes, Use the least aggressive scotchbrite pad to smooth out the primer. If necessary, go to a more aggressive scotchbrite pad.

- Mix the paint, reducer, and hardener according to specs (I forget the ratio)

- FIll the spraygun with the cheap paint and practice your spraying technique on an old Costco box

- Spray a reservoir full of lacquer thinner through the gun to thoroughly clean it out

- Wipe it down with Prepsol

- Spray about 20 or 30 minutes after the primers dried but don't wait much longer.

- A quart is plenty of paint for a car roof, don't be afraid of running out, take your time spraying per the instructions above.

- Wait about 20-30 minutes, use the least aggressive scotchbrite pad to smooth out the paint. If necessary, go to a more aggressive scotchbrite pad.

- Spray a reservoir full of lacquer thinner through the gun to thoroughly clean it out

Make sure it's no hotter than 80 degrees and no colder than 55 degrees when you do this.

You'll be doing this more than you think so the tools are worth the investment.
I've done this several times with acceptable results.
I know most people would consider it a halfass job but sometimes the best job is that which is complete (and we're not spending nights/weekends for months trying to get it perfect).
 
  #12  
Old 04-25-18, 09:18 AM
Member
Join Date: Dec 2016
Location: Canada
Posts: 233
Received 0 Votes on 0 Posts
Repair

Some of the tips here are great if you want to do an oem quality repair. But I fear the leading edge has a bit of rust right down into the trim area, so unless you remove the trim, the visible part may re-rust from the hidden part anyways. Removing trim without damage can be tricky. Spot blending in a repair without doing the whole roof is also tricky, especially with a metallic paint.

To be practical, if the objective is to stop the rust, and get things to look a bit better, without perfection, here is a variation to consider which is a bit hillbilly but might also be a fall back if you attempt the paint repair and it does not look very good.

Just scrape off the loose paint, sand it down to remove the rust, feather sand the patch into the adjacent paint using a 400 grit paper, use any sort of rust paint to seal it off (por 15 is excellent), could brush by hand, then just
put a black tape stripe along the whole leading edge of the roof to cover things up. The tape strip would also act as a bit of protection for the whole leading edge, I think I spot another chip on the edge of the side door frame which may be another rust spot in the making, might put a little protective tape strip on the leading edge there too. Should look fine with all the other black trim and black roof racks and you don't have to fuss with the paint being perfect.

https://www.amazon.com/LinearDesigns...auto+trim+tape

The tape comes in a 2 inch width if you need greater coverage.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description: