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I've made frames out of mdf and there are quite a few exposed edges.

How should I seal the MDF? Should I seal only the edges or seal the whole surface?

Please note that these frames are to be used for acoustic panels (sound absorbing) so ideally I'd like to have a non-reflective surface, so nothing too hard and nothing shiny. These panels will be covered in fabric so the surface can't be greasy and I'll never be able to re-treat the wood after covering it.

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    can you clarify what environment these will be in and what tolerance you have for water absorption? If you're only concerned about occasional splashes (ie, not immersion) regular paint will be fine. On the other hand, if these will be immersed and you dont want any water, you're going to have to encase it all in epoxy. – aaron Feb 9 '17 at 13:56
  • The only water that is likely going to go near these panels is moisture in the air. I live in a sub tropical climate so the humidity is quite high. – Luke Allison Feb 9 '17 at 15:02
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You don't actually need to seal the MDF so it doesn't absorb moisture, any more than studwork in walls, the interior components of cabinetry or the framework in covered chairs need to be sealed. Regardless of whether it's solid wood or a type of manmade board the material can be left to absorb and release moisture naturally with any changes in humidity. In any case the whole concept of "sealing" is commonly misunderstood, with only a few exceptions the coatings applied to wood don't truly seal the surface off from water vapour*.

However, it looks like the natural colour of the MDF won't suit the completed panels so I think you need to paint them.

Normally when someone is looking to paint MDF the recommendations are about how to get the surface looking good since it'll be on show (e.g. filling/sealing the edges, then primer and finally paint, with quite a bit of sanding thrown in there). But here it seems like you really only need to change the colour so you could go straight to paint. Matt black seems like it would be the ideal colour.


*This is why even a fully varnished tabletop will still expand and contract through the seasons as humidity goes up and down.

  • Interesting that you're so adamant that I need to paint the frame. I never mentioned anything about the colour of the fabric. It'll actually be a light dusty grey and the inside of the frame will be the colour of "earthwool" insulation, which is a slightly darker brown-ish colour than MDF. The contrast probably isn't going to be great enough to justify painting the MDF. I'm just concerned about the MDF blowing up like I've seen many times before in workshops. – Luke Allison Feb 10 '17 at 3:15
  • I wouldn't call it 'adamant', just seemed liked it could be useful to have it darker while also giving you the non-reflective surface you sought. Anyway if you're especially concerned about the MDF not holding up to humidity as you've seen in the past I can't help but think you should have bought MR-MDF, I don't know what it would be called where you are but over here it's often referred to generically as medite (much like hardboard is called masonite, esp. in the US). – Graphus Feb 10 '17 at 8:42
  • if you paint, you will want to prime first. MDF will drink up that first coat nearly instantly. Oil-based primer should go without saying. – aaron Feb 10 '17 at 14:34

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