Another MDF painting question...

1 Mar 2010
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United Kingdom
Hi all,

I need some help please.

I am making a bath panel from MR MDF and want it finished in acrylic paint to match the existing paint scheme.

Which of the following methods will give me the most waterproof result?

1) Acrylic primer, acrylic undercoat, acrylic top-coat.
2) Oil primer, oil undercoat, acrylic top-coat
3) Other?

Are there any issues with acrylic paint adhering to oil based undercoats?

many thanks

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I have some Johnstone's Trade Acrylic Durable Matt to use up. The back of the tin says I should water it down to seal absorbent surfaces, but it also says to use a primer on bare timber.

I am not sure whether either of these methods is best to protect MR MDF though.

Any thoughts?
Using a Matt paint would not protect the Mdf from absorbing water and moisture, the closest finish you could get to the Matt would be to use a low sheen satin which would work.
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The only other thing you could do would be to replace the mdf with exterior grade ply wood
I thought Acrylic Matt paint would provide protection?

Although I am making a bath panel, I very much doubt it will get more than the very occassional splash.
What works for me is making up some weak oil gloss and simply soaking the MDF until it will absorb no more. - then paint it with whatever you like - the MDF is sealed by the oil gloss.
Thanks Joe-90,

Do you rough up the gloss before doing the undercoat/topcoat?
You don't really see it as it soaks into the board.
The acrylic paints I have used on MDF, being microporous, have eventually allowed water to penetrate and expand the material (believe this is one of selling points of acrylic: it allows the wood to breath), hence, though I still use acrylic primer/undercoat (Joncryl), which seems ideal for MDF, I generally finish with an oil based paint especially where the MDF is likely to get wet.

On the other hand, the acrylic floor varnish I have used on natural timber eg stripped furniture seems incredibly hard wearing so perhaps there is a none porous acrylic paint available?

Generally it is good practice to apply a soft layer (oil paint) over a hard layer (acrylic) but not the reverse as, with many substances – French polish, render I’m told – crazing may occcur.

In areas subject to constant damp use the green water resistant MDF.

Those who appreciate the value of mini rollers for applying paint may be interested to know – at least it’s new to me – that you can buy felt covered sponge rollers which seem more absorbent and don’t leave the orange peel effect resembling a poor spray job.
After a bit of thought you could give the bottom edge a gloss over as you wont see it anyway that's the only place the water will really sit there the rest should be fine. If you haven't already bought the Mdf then do consider the plywood idea, a bit more expensive but less problems you may occur
Can you apply acrylic over gloss?

Do you have to rough it up with some sandpaper first and, if so, would it retain its protection?
Ahh, missed the "crazing" comment. My mistake, sorry.

I am surprised that there isn't a solution which is both reasonably water resistant and with a matt finish (oil-based matts tend to be more 'satin').
With all said and done i myself would just go ahead and paint it with the Matt you have, just give that bottom edge that will be touching the floor a couple of coats of any oil based paint just to protect it from absorption. A bit contradictive of me but I give advice on problems that can happen but the Mdf would last a number of years just by itself really unless you put it in the bath with you lol

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