Sealing MDF -non-greasy, acoustically-transparent

[lukeallison]

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 (permeable) 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.

[Cal]

I would think any oil based or water based varnish would do the trick. 2 coats with a light sand between the first and second coat.


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[woodPixel]

Haymes Tri-Coat.. It's a sealer, undercoat and sand able base all in one.

Virtually everything I make has some mdf in it and the tricoat has been used for years. It's very nice.

[bsrlee]

If the boxes are totally covered in cloth and not exposed to moisture at all (like a cold glass on a humid day) then you really don't have to finish the boxes at all. If they are placed in areas of high humidity then a coat or two of some finish (spray cans give a light coat, lighter than brushing) will stop them going mouldy.

[Walshy]

Just a comment: you don't need to worry about sealing the MDF. It has a hard & smooth enough surface that even unfinished MDF acts as an acoustic reflector at any frequencies where the finish would matter. The fabric covering (possibly with a bit of wadding or foam beneath) does all the high frequency absorption.

While thin MDF panels with an air gap behind can act as a low frequency absorber, the finish on the MDF won't affect that, as it relies on the whole panel bending.