sandblasting concerns??

[shamus11]

Hi there,

I was speaking to someone I'd believe had fair credibility on the matter and he told me that sandblasting steel that is under stress such as a bike frame or steel monocoque car shell can have the effect of "work hardening" the steel making it brittle and pron to cracking.

He suggested that in race car preparation it is not a common practic for this reason.

What is peoples thoughts on this? I've had plans to sandblast the underside of my 240 but have decided to buy some paint stripper this morning and give that a go as a first option.

[DatsunZGuy]

Intense sandblasting with the wrong media can result in excessive friction/heat, which will warp metal if you are not careful. I can see where too much may effect the metal's properties.

[ncz]

That may be one of the reasons for the popularity of the new "plastic" blasting media. Local guy told me it didn't build as much heat and less warpage

[Bonzi Lon]

Using sand at the wrong size and too high of pressure will cause heat, warpage, and even burn thru. Ask my parents about the lawn furniture I blasted for them years ago. On the other hand, if your car is not able to rotate you will end up with a face full of chemicals. The choice for most car nutz is nut shells (walnut/pecan, etc.) they don't raise the heat so much. Another media I've heard of is baking soda. This will leave a film that will not allow rust to form untill washed off, and this MUST be done before any paint goes on. They use this at a much lower pressure and it seems to work for the guys I've talked with. Less heat and warpage. Hope this helps.

[onuthin]

I have been wrestling with this dilema for a while.I just came up with the idea of using lime.It is real fine and non acetic.It is very cheap.Has any ever tried this? I think I am going to try it on a parts car first so if it don't work I won't hurt anything.Any other ideas would be appreciated.

[a7dz]

I guess a couple of question that you need to ask yourselves is why am I sandblasting this in the first place? Is it to remove rust? Is it to remove all the paint. Why? Is there an easier less evasive way to get the work done. In some cases yes and some cases no. The risk of work hardening of the metal also happens when you shrink the sheet metal during sheet metal repairs, weld in new panels, re-chrome or re plate parts. I have done all of the listed things and probably some more I have not thought about. I do not think there is a one answer fits all in these cases. Rust repair is done best if you can remove it completely. We all know that, that is not always possible or cost effective. So, I have used many different processes depending on the circumstances and is this part structural or cosmetic.

[ZSaint]

I had some of my '71 media blasted and sand blasted the surface rust areas. The walnut shells will not take out the rust... Sand will! You need the sand to clean out the areas under the battery and behind the fenders. I used fine sand and did just enough blasting to get the surface rust off. It is a labor of love!

[EScanlon]

Intense sandblasting with the wrong media can result in excessive friction/heat, which will warp metal if you are not careful. I can see where too much may effect the metal's properties.

Emphasis mine.

This says it most accurately.

The emphasis I placed on: Intense, Wrong and Excessive are all words that can be inserted into just about any process and render it ..... harmful.

If you insist on micro-examining every possible way in which something can be done wrong.....well you might as well do nothing, since there isn't any process to remove rust that isn't in SOME manner.....harmful.... if viewed through the wrong point of view.

Are you removing metal? Yes, but metal that has rusted. Is it possible to reverse the rusting process? Possible...maybe. Practical? Probably not. Then again, how much did you want to spend on it? If money isn't a consideration, then heck, get a hold of Nissan and ask them how much it would take to build you a brand new never molested Datsun 240 Z of 1970's vintage.

The bottom line in any of the processes being discussed; sandblasting, undercoating, bondo, welding, brazing, etc, is that it needs to be done PROPERLY and CORRECTLY.

There are various methods for any one of the items I mentioned, but your expertise, funds, time, and WHERE you have to work, all play a factor in how well the job will be done.

A7DZ's comments are on-line as well. WHY you are doing something is as important as HOW you are doing it.

I do not think there is a one answer fits all in these cases. Rust repair is done best if you can remove it completely. We all know that, that is not always possible or cost effective. So, I have used many different processes depending on the circumstances and is this part structural or cosmetic.

If it were in fact EASY, then ANYONE could do it. The methodical care in HOW you do it is what distinguishes a craftsman and a back-yard hacker.

I think that in the majority of these processes the key lies in being careful and not get overly agressive.

FWIW

Enrique

[shamus11]

The main reason I'm looking at sand blasting is time. I want to bare metal the entire bottom of the shell so I know what I'm dealing with, and I want a good clean new finnish underneath.

At the rate I'm going thru strip disks I'm thinking I could buy a small sandblaster and have a reusable tool at the end of it all. I already have a good size air compressor.

[ZSaint]

Here's what I did... I bought a larger sandblaster at Harbour Freight. I think I paid $100 for it on a special discount. I bought cheap sand and that was a MISTAKE. It kept plugging up. I had to filter the sand with a screen several times to get only the small particles. Trust me, if I were doing it now I would have bought expensive sand just for sandblasting. Once I got the sand filtered the blaster worked and did not work. I got the job done but it was a hassle. GET THE RIGHT SAND!

[EScanlon]

Good abrasive material, whether sand, oxide, glass, or nut shells should'nt need to be screened in order to be used....but...it isn't a bad idea to screen it anyhow. That just simply ensures you that there are no "clumps" to surprise you.

You CAN use "el-cheapo" playground sand....IF....and that is a big if...you take precautions. As Zsaint mentioned, you'll need to sift it and ensure it IS dry. If it has ANY kind of moistness in it...it will clump, and usually at the most inopportune moment AND deepest in the equipment. You'll also want to use a good dust mask. Playground sand will undoubtedly have a lot of Quartz in it, which when pulverized means Silica dust floating in the air. You don't want to inhale that dust.

You'll want to build a containment screen. Whether that's a full blown tent or simply a tarp screening your blow-by from scattering to the 4 winds is up to you and your situation. But it CAN be done. Look in my gallery for my sand-blast booth in my driveway.

Good Luck

Enrique

[a7dz]

I used masonry washed sand. Worked very well. Very fine and I too sifted it as I reused it to keep any lumps and foreign particles out of the blast hopper and hose. Biggest deal is keep it clean and dry and wear a mask. I personally use a respirator to keep the silica and rust particles out of my lungs. This past week I spent some time with Enrique and his play ground sand worked every bit as good as the masonry sand. Just follow his post above.