What primer should I use on Moisture Resistant MDF to be fitted in bathroom?

Discussion in 'Carpenters' Talk' started by SimoneLola, Nov 26, 2020.

  1. SimoneLola

    SimoneLola New Member

    Hi everyone
    I really hope you guys can help. I’ve bought moisture resistant MDF to put in my bathroom and I need to prime it. I’m getting all sorts of conflicting advice how to prime it.

    Does anyone know what I should use?

    Many thanks in advance.

    Simone
     
  2. Red Star Boats

    Red Star Boats Active Member

    Zinnser bin shellac primer, for initial sealing followed by Leyland acrylic primer / undercoat, then two coats of whatever paint finish you want. Make sure you sand all cut edges up to 320g before priming and between all subsequent coats, break any sharp edges with abrasive too, paint does not like really sharp corners, it will fail and run the risk of moisture getting under the paint.
     
  3. SimoneLola

    SimoneLola New Member

    Hi Red Star Boats

    thank you so much for your reply!

    what do you mean by “Make sure you sand all cut edges up to 320g”? Is that the coarseness of the sand paper?
     
  4. Red Star Boats

    Red Star Boats Active Member

    Yes, abrasive is graded by grit (g). Start with 120g then 180, 240 and finish with320. As for the sharp edges they don’t need to look rounded over a quick rub along the sharp edge with 180 should suffice, this is known as breaking the arris, believe it or not!
    Perhaps should clarify only need to sand cut edges that will be seen and therefore require painting, edges covered during construction only need to flat and square.
     
  5. Astramax

    Astramax Super Member

    Any reply would be conflicting advice...surely:confused:.........sad but true.
     
  6. Red Star Boats

    Red Star Boats Active Member

    Unless two people advised the same thing, sure that’s unconflicting advice! If that’s true maybe I’m the sad one!!
     
  7. Astramax

    Astramax Super Member

    Well he's now totally bewildered. :confused:
     
  8. SimoneLola

    SimoneLola New Member

    @RedStarBoats

    should I prime the sheets before I put them up?
     
  9. Astramax

    Astramax Super Member

    What are you doing with the sheets.
     
  10. SimoneLola

    SimoneLola New Member

    I’m using them to clad a bathroom. They are bead and butt.
     
  11. Astramax

    Astramax Super Member

    How do you intend to finish these boards, are you painting, tiling, over cladding etc.
     
  12. SimoneLola

    SimoneLola New Member

    I want to finish with paint that’s suitable for a bathroom. I’m worried about priming because as it’s MDF and it’s going to be in a bathroom it has to be treated to withstand the moisture otherwise the sheets will become out of shape. If I were to use a water based primer it will ruin the MDF.
     
  13. Red Star Boats

    Red Star Boats Active Member

    You can use a water based primer, that is what the Leyland Acrylic is, but it’s a bit more tricky than BIN if your not used to it. The BIN will give you a good base to work from and seal the mdf with less reaction than Leyland first. Moisture resistant mdf is what is says, resistant to moisture, it never hurts to prime both sides but it’s not essential.
    I often wonder who the people are whose bathrooms get so steamy the paint fall off the walls, decoration aside good ventilation is must in a bathroom, get this right and you can pretty much decorate how you want, just don’t let puddles of bath water sit around, clean up after yourselves and everything else will look after itself.
     
  14. SimoneLola

    SimoneLola New Member

    I’m going to follow your advice. How many coats would you recommend?
     
  15. Astramax

    Astramax Super Member

    Best advice would be do a test piece first, how well does wet acrylic paint stick to a moisture resistant coating.
     
  16. SimoneLola

    SimoneLola New Member

    Would this be better?
     

    Attached Files:

  17. Astramax

    Astramax Super Member

    In this instance may well use Zinsser Bullseye 123 and give it the full curing time.
     
    NannaT likes this.
  18. Nanook

    Nanook Active Member

    I’m in Astramax’s bad books at the moment but nevertheless Astramax has the upper hand here because they have been doing this for a lifetime. No offence Red Boots, I’m taking your oil advice and running with it.
     
  19. SimoneLola

    SimoneLola New Member

    Wow I’m beginning to regret wanting to clad my bathroom with this moisture resistant MDF stuff!

    So I’ve been watching some YouTube videos and zinnser bullseye 123 seems to be the answer...

    In a nutshell can you advise me what to do step at a time pretty please with a cherry on top.
     
    NannaT likes this.
  20. Astramax

    Astramax Super Member

    Screwfix will probably be the best place to buy regards cost circa £29 for 2.5lt, follow instructions on container and apply using a 1.5" brush and 4" roller. To save me writing war and piece it would be best to follow the videos on You Tube.
     
    Last edited: Nov 27, 2020
    NannaT likes this.

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