Surface prep for painting


Old 11-02-04, 09:41 AM
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Surface prep for painting

Now that I'm starting to get the hang of welding, I realized that my creations will rust (ok in some cases) unless I paint them. Any advice on how to clean and prep the metal before painting would be greatly appreciated.

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Old 11-07-04, 04:19 AM
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Unless you make perfectly scalloped weld beads where all the slag comes off with a tap of the chipping hammer, you'll probably have to resort to using an angle grinder and/or sandblaster to clean the welds up for painting. The angle grinder is an indispensable tool for prep and cleanup: I use grinding and flap wheels to remove not-so-good welds and put a quick bevel on mating surfaces; cup brush and knotted wire wheels for removing slag from good welds. For mediocre welds - ones that are serviceable but not exactly show quality, let's say - I use a completely different tool to prep a weld for painting: the sandblaster. Nothing is faster or more thorough at removing slag, rust, scale, etc. Of course, nothing is more unpleasant to use than a sandblaster - the sand stings when it ricochets back at you and gets into every nook and cranny - and they do require a decent sized air compressor even if only used in short bursts. I got a Campbell Hausfeld "shoulder carry" sandblaster from Home Despot years ago but they quit carrying them (probably because none of the portable compressors they sell can keep up with one); you'll have to go to Harbor Freight or similar these days. Keep in mind their high demand for air. My 5.5hp gas Emglo compressor delivers an honest 9.5 cfm at 90 psi and it is just sufficient to let me run my sandblaster continuously for 1 minute before the pressure drops below 80 psi. Still, in that 1 minute I can clean up 4 inside corner welds on 1" square tubing (try doing that with an angle grinder!).

Oh - if you are stick welding aluminum (yes, it can be done) then you can remove the slag by simply scrubbing with hot water and stainless steel brush. The slag is composed of fluoride salts that are very soluble in water.
Old 11-07-04, 09:33 PM
Join Date: Mar 2000
Location: Lake Murray, SC USA
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tesseract - great post. Only thing I could add is to wipe the steel down with a rag soaked in naptha or acetone to remove the protective coating that comes with mild steel to prevent rust. Obviously only wipe cold steel with flammables or you will have other problems...............FIRE!
Old 11-09-04, 12:15 PM
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Great advice, thanks

Thanks to both of you for your input!

I'm in the finishing stages of my first project - a snow sled I made by cutting 4 old skis in half and mounting to a metal 1" square tube frame I made. My son and I found some old plastic school chairs that we cut the legs off of and mounted to the top of this thing.

Once it's all painted up, we're ready for our trial and error testing!
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