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I have a question regarding the exterior painting prep. Should the cleaning with TSP be done before scraping and sanding? Or, should it be done after the scraping/sanding? Some articles say that the cleaning is the first step before any prep job but I also find other articles saying that the cleaning is done after the scraping and sanding to wash away dirt and debris.

What is the right order for the prep job?

  • What is the surface material? – diceless Apr 21 '15 at 4:14
  • It's wood siding. – DSKim Apr 21 '15 at 7:24
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TSP last.

If you use TSP first you'll be wasting your time cleaning paint that you're just going to scrape off anyway, and the old primer/paint/wood beneath what you scrape off will remain uncleaned. If you use TSP first, that also means the chips and dust from your scraping and sanding won't be washed off. So TSP should always be your last step.

  • I agree. Especially if you have older paint. Older paint will come off in larger chips and will expose larger amounts of the surfaces below. As such if you clean first you'll just have to do so again later especially if you sand. You really don't want sanding dust below your paint. – Dano0430 Apr 21 '15 at 15:18

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