Trisodium Phosphate / Painting / Sand Paper Questions

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  1. #1

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    Trisodium Phosphate / Painting / Sand Paper Questions

    Quote Originally Posted by RMDNC:
    You want to remove the dust and clean the surface before priming. Use TSP.https://www.youtube.com/watch?v=RyVT4vKIcN8
    Where can one get TSP in HK and what is it called in Cantonese (any Chinese characters would be helpful)? I am also looking for Methylated Spirits / Denatured Alcohol.. can anyone also provide the name in Cantonese (Chinese characters if possible)? These items may be useful for me in my attempt to clean / prep a door for repainting. Lastly, what grit sandpaper is the best to use to lightly sand the door before repainting it? TIA

  2. #2

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    Quote Originally Posted by hkgcat:
    Where can one get TSP in HK and what is it called in Cantonese (any Chinese characters would be helpful)? I am also looking for Methylated Spirits / Denatured Alcohol.. can anyone also provide the name in Cantonese (Chinese characters if possible)? These items may be useful for me in my attempt to clean / prep a door for repainting. Lastly, what grit sandpaper is the best to use to lightly sand the door before repainting it? TIA
    If the existing paint isn't peeling and you're going to paint it a similar colour why not just sand and paint?

    Again sandpaper will depend on the existing condition of the door. 100-150 should do and then -200+ before painting.

  3. #3

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    Quote Originally Posted by hkgcat:
    Where can one get TSP in HK and what is it called in Cantonese (any Chinese characters would be helpful)?
    Trisodium Phosphate

    Formula: Na₃PO₄

    Leads to

    https://zh.wikipedia.org/wiki/%E7%A3...85%B8%E9%92%A0

    Check with a chemist / pharmacist or someone who knows chinese and some chemistry

  4. #4

  5. #5

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    Quote Originally Posted by shri:
    Trisodium Phosphate

    Formula: Na₃PO₄

    Leads to

    https://zh.wikipedia.org/wiki/%E7%A3...85%B8%E9%92%A0

    Check with a chemist / pharmacist or someone who knows chinese and some chemistry
    Yes, old school. There's not enough space to store the liquid so they'll give you the powder chemical wrapped in paper and you mix it yourself.

  6. #6

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    Quote Originally Posted by Cornmeal:
    If the existing paint isn't peeling and you're going to paint it a similar colour why not just sand and paint?

    Again sandpaper will depend on the existing condition of the door. 100-150 should do and then -200+ before painting.
    The old paint on the door isn’t peeling, it’s just yellowed from age and had cracks in the seams (door has wooden frame with glass panels). The cracks in the seams I already filled with putty then sanded with 1000 grit sandpaper (which I already had on hand). This same grit was ok sanding down the putty but was hopeless on the old paint coz too fine and just got clogged up immediately. I want to sand the old paint just to provide some key for new paint to adhere properly. Do I need to use 2 types of sandpaper — 100-150 first and followed by 200+? Or one type is sufficient (what grit)? Also, do I need to use a primer before painting? For reference, old paint most likely oil-based (factory finish) and new paint will be water-based (Nippon aquatec wood brushing finish). Both are white colour. Just wanted to make sure I prep the surface enough for the new paint to last a few years. First time repainting a door..

    Btw, I asked about TSP as interweb suggests to clean with it first before sanding. Did you say no need to clean it before sanding?

  7. #7

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    Quote Originally Posted by hkgcat:
    The old paint on the door isn’t peeling, it’s just yellowed from age and had cracks in the seams (door has wooden frame with glass panels). The cracks in the seams I already filled with putty then sanded with 1000 grit sandpaper (which I already had on hand). This same grit was ok sanding down the putty but was hopeless on the old paint coz too fine and just got clogged up immediately. I want to sand the old paint just to provide some key for new paint to adhere properly. Do I need to use 2 types of sandpaper — 100-150 first and followed by 200+? Or one type is sufficient (what grit)? Also, do I need to use a primer before painting? For reference, old paint most likely oil-based (factory finish) and new paint will be water-based (Nippon aquatec wood brushing finish). Both are white colour. Just wanted to make sure I prep the surface enough for the new paint to last a few years. First time repainting a door..


    Btw, I asked about TSP as interweb suggests to clean with it first before sanding. Did you say no need to clean it before sanding?
    Yes, I find using 1 lower grit to take off as much as possible then a higher finer grit to smooth it over while still leaving some "teeth" behind to take up the paint works. However the only caveat would be if the original coating is oil or alkyd paint and the new cost is acrylic/latex paint as the former can go over the latter but not always the other way around.

    https://artradarjournal.com/2021/11/...based-paint/#1

  8. #8

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    @Cornmeal Thanks for the explanation about sand paper. I went to a paint store near my place and they seem to have sand paper in different colours, not just black. If it is the same grit, will it matter what colour the sand paper is?

    Also, further reading online seems to strongly suggest after sanding old oil-based paint, to use a primer before applying water-based/ latex paint. Is a primer really necessary in this situation and does it matter if the primer is oil-based or water-based? I checked and Nippon Paint only has water-based primer.

    Really appreciate your advice!


  9. #9

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    After filling in the cracks in the seams of my wooden door with putty, and sanding the putty with 150 grit, just read the label on the putty container and it does not mention for wood, just mentions cement plaster, concrete and bricks. Guess it is meant for wall? Did I just mess up and have to redo by buying a wood putty? Or is putty for wall ok to use for wood too, even if it does not say so on the container?