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flap wheel dust (from steel) magnetic?

I have been building steel stairways inside new town houses, which are of course made of wood & drywall. The builder called me just now and said his drywall screws are beginning to become visible, through the paint, texturing and mud. He thinks that when we sand off the welds (from the square tube, which we do to make the handrail feel smooth to the hand) that the swarf is magnetized and is "finding" the sheetrock screws and sticking there, making them apparent to the eye.

Is this possible? It seems to me that if it were, several things would have to be demonstrably true:

  1. the effect would be much more pronounced in the stairwell than in the rest of the house

  1. dust carefully collected onto a card would be attracted to a paper clip or other steel object

  2. a lot of the dust would be hanging onto the stair railings and beams themselves.

Anyone have any ideas or information about this?

Grant

Reply to
Grant Erwin
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Is the work you are doing happen before the house is taped? Steve

Reply to
Up North

Grant I do quite a bit of grinding using flapwheels and I have noticed the pieces I grind do get magnetized, more so when the flap wheel is worn. This problem reared it ugly head in the paint booth. I just checked some of the dust with a piece of steel that is not magetized and it appears that the dust is not magnetic. It seems like the amount of dust sticking to a sheetrock screw head wouldn't cause rust to bleed through. I am thinking crappy imported screws with poorly done phosphate coating. Steve

Reply to
Up North

I have been welding and grinding in these stairwells both before and after the walls were sheetrocked. However, I never worked with the walls rocked but not mudded or taped - either bare studs or finished walls.

Grant

Reply to
Grant Erwin

I think the drywall screws are magnetized, even before they get driven with magnetic screwdriver bits. To test this I stuck a handful of drywall screws (fresh out of the box) in the swarf pile on my bandsaw. I cut a fair amount of steel on that saw. Most of them came up with lots of bits stuck to them. A few did not. To see if the swarf was magnetic, I stuck a couple of different pieces of steel into the swarf and nothing stuck. I think the drywall screws are stamped or forged, and I think that impact can cause weak magnetization. The blacksmith guys would know more about this than I do.

I used to work in a shop that was built with sheetmetal beams and drywall screwed to them. On the walls behind the chop saw and grinders you could see every screw outlined with swarf. A year later, you could see the beam outlines.

Good Luck, BobH

Reply to
BobH

Obviously the builder is a wood guy.

The screws are magnetized if anything. The box might have set next to something in the truck - mag base or another tool.

The screws might not be quality - e.g. Chinese and not real black oxide. Thus when the mud was put on, they rusted.

Lots of stuff to think about.

Good luck. Seems the wall would have been spotted in the tape and bedding as well - if dust borne. I can't believe the whole wall clean and then just the screws. Something is rotten with the sheet rock guys.

Martin

Mart> I have been building steel stairways inside new town houses, which are of

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Reply to
Martin H. Eastburn

I've seen several places where metal framing could be seen through the drywall as it aged due to accumulation of metal particles.

Steve

Reply to
SteveB

'strue. Take a steel nail, point it north-south, and whack it with a hammer. It'll magnetize.

Reply to
Tim Wescott

The mixed oxide Fe3O4 is magnetic; it's what the natural ones are made of.

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A lot of it collects on the edges of the mag chuck on a surface grinder. Sometimes the iron in the swarf ignites and burns but it doesn't fall off.

Reply to
Jim Wilkins

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