Sandblasting vs. Rust?

Hi all,

The entire floor of my '77 Datsun 280Z has rust rot. In fact, the frame rail crumpled under the weight of the jack! My colleague is also an auto welder and said for a few hundred bucks he can weld in a new floor pan / frame rails (basically at cost). On the other hand, I also understand that sandblasting removes paint but is it effective for rust as well? (Ignoring the cost) I’m debating whether sandblasting would be worth the investment or whether it would be superfluous, in other words, welding a new floor pan / frame rails would be sufficient to eliminate rust.


Sandblasting will find bad areas you thought of as ‘structurally sound’ before so get ready to get a boat load of replacement panels and welding wire.
If your floors are rotted, there’s very good chance rockers are bad as well.

Sand basting would be effective against surface rust, but totally useless for anything but surrounding areas of all parts that need replcement. The only real cure for structural rust problems is to cut out, remove and replace.

There was a metal quanset building on my campus. A quanset hut is essentially a self supporting structure rather like a unit frame construction. At any rate, the building was remodeled,and the outside structure sand blasted and then painted. We had an ice storm in the area and the building collapsed. The sand blasting was blamed for weakening the structure. This happened 31 years ago. There was a physical education class in the building, but fortunately all got out before the building went down. Maybe my fears are unfounded, but I would worry about sand blasting the undercarriage of a car because of weakening the metal.

It may be time to part the car out and say goodbye to what remains, if anything. Odds are the rust has gotten to everything on that car from one end to the other and you would be fighting a losing battle in an attempt to fix this.

Normally you’d want to blast the areas prior to repair so you have a good surface to weld in the new sections. Sand blasting is not an alternative to replacing rotted out sections that are not structurally sound.

Thanks everyone!!

Based on your helpful comments it seems like sand blasting is related more to surface rust / paint, but would not address the structural issue of rust which is obviously my main concern. As everyone indicated, sand blasting is not a substitute for cutting & welding.

I just started restoring the car and was debating whether to completely strip it down to the unibody for a rotisserie restoration - kind of a “while I’m at it” consideration. While it may be a good learning experience it sounds like it would indeed be unnecessary. Moreover, since I have access to a lift I can work with my friend and weld in replacement surfaces (which would obviously be a good opportunity to learn how to weld).

Well, you first need to identify all the rusted areas. And it sounds like you’ll need to find somebody with a ramp-based lift, since you can’t safely put it on a pad lift. I have a bad feeling that floor pans are the least of your problem. Rust this extensive may make the project a no-go, unless you are happy putting in thousands to get back hundreds.

Sand blasting is a good way to identify the rusted out areas. It’s NOT a way of fixing the rusted out areas. I’d sandblast first then get all the rusted out areas replaced with new metal. If you can’t find a floor pan for that car…then you’ll need to get metal that’s THICKER then the floor pan metal currently is. Floor pan is made stronger by adding ridges into it. You won’t have that if just sheet metal is used.

If a you are restoration. This a car I would strip down and have dipped or media blasted. It will show you what will need to cut out and replaced. It well worth it saves a lot of work and money in the long run.

I really appreciate everyone’s input!

I did some more research and spoke with some other folks in my area. They said with a little instruction I could certainly learn to weld in new floor pan, rails, rocker panels, etc. But if it requires extensive work (for example to the point of having to sand blast and/or having to put it up on a rotisserie) that it would require more extensive skills & experience. In particular, when heating the unibody great care must be taken to ensure it remains true. Otherwise it will warp. At that point I suppose it would not be worth the investment, regardless any sentimental attachment of owning the car for over 30 years. :frowning:

You wont warp the unibody by spot welding. Mig welding is not to hard to learn,but If replace a rail get someone with experience to help you. Floor pans are not bad if you take your time. If you can find a place to have it dipped, that would be best. Dipping get all the rust and show you were its at. Also stops it. Then it just a mater of cutting out bad areas and fixing them. I have had some cars dipped and it just makes it so much easier to work on. Look for some you tube video’s on welding and body work. Don’t worry to much over it. Its only money and you find away to spend anyways. If you can save the car and have some fun working on go for it.

Note that sandblasting can easily warp panels.
Has the car been repainted at all? If so, all sorts of badness can be hidden under bondo. In that case, even careful sandblasting can turn panels into Swiss cheese in no time.
A rotisserie restoration will be really expensive and lengthy because everything has to come out of the car. Besides it taking a lot of skill and labor, it takes in a lot of space in a shop for a long time.
It will be expensive.

Nobody can tell you what a car you’ve held onto for that many years will be worth to you but just understand that you’ll never get that money back.
Just know what you’re getting into.

“They said with a little instruction I could certainly learn to weld in new floor pan, rails, rocker panels, etc.”

You’re joking, right? If this is your first welding experience, and you do this, never take a passenger in the car. Please. Minor patch panel welding, sure, but you’re talking structural repairs. Not where I’d want to be learning.

I agree with Texases post, and emphasize especially USE A RAMP-TYPE LIFT.
If you put this on a pad lift and the rust is extensive, it could collapse on the lift and you could be hurt. Consider it unsafe for a pad lift until you can confirm otherwise.

Also PLEASE do NOT try to inspect the underside by putting this on jack stands and sliding under. If a jack stand punches through rotted metal while you’re under there, it could crush you.

IMHO, the only way you’re really going to be able to get into this project and end up with a good safe restoration in to gut the interior, pull the windows and trim, pull everything mechanical off, clean at and around the suspect areas with a media blaster (various types of media are available, including sand), and thoroughly check for rust and rot. Just welding a new floor in IMHO is unlikely to be safe. You really need to assess the condition from a structural standpoint.

As to the welding itself, there are a number of companys out there that make steel replacement panels and “clips” for these cars. IMHO the best way to get a safe car is when you find a rotted area you get a replacement section/clip/panel in steel, cut the old one out, and replace the whole area.

As a matter of fact, I’ll bet there are websites out there and books specifically devoted to restoring these cars. They were classic automobiles. There’s a whole “Z” subculture out there.

I agree with oldbodyman on the dipping. Sand will warp panels like most have said here. It also leaves you with a rough surface that you will have to smooth before re-applying paint. Now I know you have been talking mostly about the bottom of the car but they will not be able to ensure the rockers don’t get blasted to. Any paint removal is a $ value somewhere. Pay upfront with dipping instead of panel prep afterwards.

If you’re looking to learn how to weld, look into night classes. Some technical high schools offer welding as an adult class.
Welding isn’t difficult but to learn it from someone that actually knows it beats learning it by trial and error.

I personally think that you have bitten off way more than you can chew.

If the floors and side rails are rusted out it is highly likely there is significant rust damage at all of the suspension mounting points and at other important structural areas.

I also don’t think you have a full grasp of what Uni-body construction entails. In a Uni-Body vehicle there is no separate frame, the pressed metal panels serve as both body and frame hence Uni-Body (Actually UNIT BODY), the body and frame are an integral unit. So when you say you can replace the floors and side rails without affecting the uni-body, you are mistaken. The floors and side rails are almost 40% of the Uni-Body.

The payback to restore this car is likely not enough to justify the expense to fix it correctly, IMO. To fix it correctly, you need to identify ALL of the rust damage and previous body work as well and then repair it all. This means stripping this car down 100%, media blasting the metal (NOT sand blasting which WILL tear up the metal - blast with baking soda or walnut shell media). THEN you will know what it will take to fix it right. Doing a half a$$ed job of welding in a couple floor pans will leave a vehicle of questionable safety that could fail catastrophically at any time.

Sand as a media is for heavy gauge parts or hidden stuff. Other media (plastic beads, baking soda, walnut shells) can be used for body panels. It’s far cheaper than dipping (in my experience) and there are places you can haul the rolling chassis to that will do the stripping for a reasonable fee. Last time I was stripping an entire car I checked on the U Strip options. It was only like $200 more money to have them do it versus me renting the booth. Here’s your $200 extra, I’ll be back in two days to pick it up…

Way back I worked on one of these cars and a good portion of the rails under the floor were mangled/compacted towards the floor from people trying to jack the car up to high without distributing the load on one side of the car. Is it possible that we are thinking his rust is much worse than it really is?

And no car is too far gone if it is something you want to do. If you are paying someone else then I would agree but the mere satisfaction of completing things like this yourself will be a good booster of your energy in building this car. Parts are mostly available and knowing you did it will be a plus also.

Uni-body/Unit body construction though is very critical since you don’t have much room for error like on frame cars. I would take ton’s of measurements before I broke the first weld loose.