Paint Bubbles / Blisters then rust

[johnh]

I have two spots on my 2011 Yukon XL that the paint is bubbling or blistering.

Now here's the bad part, I've sanded it down and its all SURFACE rust not coming through on the back side. The metal under the paint/primer thin rust layer is CLEAN and solid.

So I sanded, cleaned with goo gone and isopropyl, reprimed and repainted...and low and behold over the winter blisters and bubbles in the same DAMN spot.

Anyone have any idea why?

 

[wjburken]

I have two spots on my 2011 Yukon XL that the paint is bubbling or blistering.

Now here's the bad part, I've sanded it down and its all SURFACE rust not coming through on the back side. The metal under the paint/primer thin rust layer is CLEAN and solid.

So I sanded, cleaned with goo gone and isopropyl, reprimed and repainted...and low and behold over the winter blisters and bubbles in the same DAMN spot.

Anyone have any idea why?

I’ve been down this path myself.

My guess is you have rust on the back side of that panel. It has likely created micro fissures/pores in the metal and moisture is wicking through and getting under your paint causing it to bubble. If you were to cut out that section, I would be willing to bet the back side of the piece would be covered with rust.

Can you post up some pictures of where you are seeing these blisters form?

 

[johnh]

Back Passenger side, behind rear wheel where the fender meets the plastic Fascia. This one here I treated the metal with POR-15 which is a moisture cured urethane which should stop any wicking through.

Driver's side panel bottom behind the driver's side rear (LH Rear) door in front of the wheel well...

Any way to fill stop that? If the POR15 didn't stop it, rust preventing primer didn't seal it.

Here's the thing, on both I was expecting rust on the other side, but I didn't see/feel any (at least on the passenger side). I had all the filler/fiberglass ready but only found metal no rust...which I found a bit surprising

 

[George B]

Some pics would help with this one.

 

[johnh]

This was repainted last summer/fall. (and sadly my clear coat overspray is peeling). Other side is completely fine. In fact, other than these two spots, there's no body rust at all (except for lower edge of the liftgate)

This was also redone (and I removed the fasica) as well (this one had the POR-15 on the bare metal, then primer then paint.

 

[kbuskill]

Did you put any Ospho on the bare metal before the Por-15, primer, paint, clear?

 

[Big Mama]

How high above the rusted area did you go? If single wall did you treat/paint the inside? Like Ken said some “holes” on the back side might be really small and not show rust yet.

 

[wjburken]

This was repainted last summer/fall. (and sadly my clear coat overspray is peeling). Other side is completely fine. In fact, other than these two spots, there's no body rust at all (except for lower edge of the liftgate)

This was also redone (and I removed the fasica) as well (this one had the POR-15 on the bare metal, then primer then paint.

The rust you are seeing in the area in front of the rear wheel is pretty common. In visiting with a local body shop, the guy showed me where he was fixing this same area on a Yukon XL and that there is a piece of foam like material inside that area for sound proofing. As moisture gets in there, the foam absorbs it and holds it against the back side of the sheet metal and it rusts through. The spot on the painted visible surface was about the size of a playing card but the inside had rust over an area about the size of a dinner plate.

 

[Tonyrodz]

The rust you are seeing in the area in front of the rear wheel is pretty common. In visiting with a local body shop, the guy showed me where he was fixing this same area on a Yukon XL and that there is a piece of foam like material inside that area for sound proofing. As moisture gets in there, the foam absorbs it and holds it against the back side of the sheet metal and it rusts through. The spot on the painted visible surface was about the dive of a playing card but the inside had rust over an area about the size of a dinner plate.

Same thing happens with the older Ram pickups above the rear wheels. Foam there too.

 

[johnh]

No Ospho. I figured the POR15 would stop it since the surface appeared to be ok after light sanding. I'll add it to the list for the next go around.

So I guess on the wheel well rust I need to get behind there and might as well remove the sound material and see.

I seem to remember the first spot on the back fender by the fasica was clean behind--it was easy to reach up in there..but I'll have to double check it.

Thanks for the replies!

Now I just need it to stop snowing and get warmer.

 

[wjburken]

So I guess on the wheel well rust I need to get behind there and might as well remove the sound material and see.

Unfortunately, the sound proofing is stuck between the layers of metal that are welded together. Only way to get it out is to cut stuff out.

With the fender wells, the moisture gets in between the inner well liner and the outer skin so the rust is hidden between the two pieces of metal. If you look closely, you will see where the inner liner’s flange sits on top of the flange of the outer skin and that seam is where moisture and debris gets in between them and just stays there.

 

[Drok]

Yup the bubbles are a fun thing. I had one ive been fighting with and lost ( centered above drivers rear tire) now ive got 2 more right next to the one thats all rust. Ughh... im about to just buy the rear arch and find someone that know how to do the job.

 

[MD Tahoe 13]

Had a similar problem above a wheel well. I lightly chipped/sanded the spot, applied POR 15, then topped that off with POR15 Top Coat (white), then sanded that down and sprayed just that area with summit white paint that I bought on Amazon and it looks much better. Still a little rough, but it didn't bubble up or rust again.