Priming MDF

Discussion in 'Painters' Talk' started by RolandK, Sep 6, 2018.

  1. RolandK

    RolandK Active Member

    I need to paint some MDF but using such as acrylic primer/undercoat or any thing water based in the past has always raised the fibres leaving a surface which needs a load of work. Can I use a solvent based primer/undercoat then water based topcoat? Or any other advice welcomed!
  2. diy_nixy

    diy_nixy Active Member

    You can still use water based primer and paint. You just need to sand down between the coats.

    I wont explain the whole procedure because GosForth Handyman on Youtube has done a great video.

  3. DIYDave.

    DIYDave. Well-Known Member

    Yep priming/painting cut edges of MDF does take a bit more work to get a good finish, agreed

    I always use Leyland Acrylic Primer Undercoat, over all surfaces of MDF, never bother with a specific MDF primer, 2 coats on the smooth faces gives a great base to then paint on. Light rub down inbetween all coats, P120/180

    1st coat will raise the fibres and give a rough finish, sand down and prime again. I use 4” foam roller and with a dry brush, remove overspill from faces. 2nd coat will need less rubbing down, just very quick rub over. 3rd coat of primer, repeat

    Sounds drawn out but this stuff dries in an hour max and as it has plenty of ‘body’, it also acts almost like a filller, smoothing out the cut surface

    3 coats of primer and sanding should leave you with a surface as smooth as the face. Depends how neat the cuts are in the first place though ?
    KIAB likes this.
  4. KIAB

    KIAB Well-Known Member

  5. RolandK

    RolandK Active Member

    Thanks for the info. Perhaps the MDF I've used is not so good but on one window sill it was still raising the fibres after 3 coats of primer! I'll persevere though and try the Leyland primer. I don't ever bother with trying to paint cut edges, I use iron on wood edging and get round it that way.
  6. WillyEckerslike

    WillyEckerslike Well-Known Member

    That's a good point. Some of the MDF sold in the sheds can be difficult to get a good finish on the edges. Definitely variable quality MDF around. I believe that Medite (trade name) or water resistant MDF is of better quality when cut.
  7. RolandK

    RolandK Active Member

    The MDF is from Wickes and looking at the surface the wood fibres are quite visible. I'll make sure I take a better look in future. As I said I tend to edge cut edges but in this case the surface is the problem. Or perhaps I'm just too fussy as my other half is always telling me!
  8. Astramax

    Astramax Well-Known Member

    Have you chaps never heard of Cellulose Sanding Sealer!
    Paulie1412 likes this.
  9. RolandK

    RolandK Active Member

    Tell us more......
  10. DIY womble

    DIY womble Well-Known Member

    Out of curiosity has anyone tried a heat gun on cut edges before priming
  11. Jord86

    Jord86 Well-Known Member

    PVA and water 50/50 also works, sanding between coats.
  12. chippie244

    chippie244 Well-Known Member

  13. DIY womble

    DIY womble Well-Known Member

    Heat gun
  14. RolandK

    RolandK Active Member

    That surprises me on two counts. First wetting it with that amount of water and secondly using the deadly PVA under paint!
  15. RolandK

    RolandK Active Member

    That's the sort of thing I was thinking of. Something non water based to seal it before the water based stuff goes on. Going to look up the cellulose sanding sealer Astramax referred to as well.
  16. chippie244

    chippie244 Well-Known Member

    Shellac followed by very fine wet and dry works every time and gives an excellent surface, I've also used Leyland acrylic primer and had good results, I've never tried PVA or a heat gun.
    DIYDave. likes this.
  17. RolandK

    RolandK Active Member

    Oh yeah having looked it up it was the stuff I used on my balsa planes many moons ago. Forgot all about it!
  18. Astramax

    Astramax Well-Known Member

  19. Astramax

    Astramax Well-Known Member

    Used gallons of Shellac Sanding sealer when Antique pine furniture was the flavour, applies and left overnight to fully dry hard whereas Cellulose Sanding Sealer is dry in a matter of minutes.
  20. chippie244

    chippie244 Well-Known Member

    I don't know what you were using but it dries very quickly.

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