How to Paint MDF

[dbbyleo]

I'm going to construct a built-in cabinet in my guest bedroom. Since I was going to paint the cabinets, I was thinking of using MDF for the primary construction material to save on costs. Also after examining my Armoire that I bought from Pottery Barn, it appears it's made from MDF also.

But before I got started, I wanted to understand how to paint MDF. I know enough about painting to understand that the edge grains does soak up paint and sealing the material is needed in order to keep it from distorting in the future.

I've read threads that talk about using primer, glue size, drywall topping, caulk, or a combination of both.

But I still have a few questions.

At this point, what is still not clear to me is how to handle the butted edges.

What do I need to do to treat butted edges? Do I treat it first - with glue or any of the other recommedation - or do I not do anything, but simply treat the whole cabinet once it's assembled?

Is there any specific thing I do different when I treat the edges versus when I treat the surface?

Lastly, can anyone recommend exactly what I should do and what brand of primer, glue, or whatever that I should use?

Thanks.

 

[Ukwoody]

Hi and welcome to the forum.

You have a couple of options here. I would suggest though that you build your unit, then give it a light sand over, especially on the bare edge of the butt joint. You can at this stage then put a little PVA glue over the bare edge and leave it to go off for an hour or so, thus sealing it. Alternatively you can give the edges a coat of the primer an hour or so before, then do the rest of the unit, going over the joints for a second time. You may need to lightly sand the edge back down before painting the whole unit either way.

Use an MDF primer - any make - available from most DIY stores/ merchants.

Glue? Well I generally use PVA on MDF, as it soaks in and bonds the particles well. You can also use No More nails (or similar) but I find it doesn't seem to have the strength. You can also use one of the new Polyurethene (P.U) glues. they are fab on MDF but, do expand, so you have to sand down all the joints afterwards.

And it then should (lol) last years!

Hope this helps, Woody

 

[dbbyleo]

Thanks woody.

I read somewhere else about a technique in finishing exposed edges of MDF. They suggested using drywall topping or decorative caulk and spreading it over the edge. Sand afterwards and you get a smooth edge that won't soak up paint or primer.

Do you have any comments on this technique?

 

[Ukwoody]

Thanks woody.

I read somewhere else about a technique in finishing exposed edges of MDF. They suggested using drywall topping or decorative caulk and spreading it over the edge. Sand afterwards and you get a smooth edge that won't soak up paint or primer.

Do you have any comments on this technique?

YUK!!!!!!!!!!!!!!!!!!!! LOL

Drywall topping will give a smooth finish... that will crack the first time the unit moves.
Caulk, can work, you need to spread it really carefully over it leaving it very thin. The problem is then trying to sand it back down to get that really smooth finish.

It is a problem with MDF no matter quite what you do, but if you seal it well, go back over it with very fine sand paper (Or fine wire wool works well too) and give it a coat (or even better two) of mdf primer it really should come out fine.

Oh, good quality fine car body filler works well on it, it doesn't usually crack, and sands down like glass, but I'm really not sure if you need to go to any of those extremes.

Depending on where the end grain is, could you not put a neat beading around the edge? That would also create that "Finished " look.

Woody

 

[dbbyleo]

I think you're right about the drywall technique - I hadn't thought about it like that. i think I won't even try that at all.

I hadn't thought about using a bead, but will in areas that might be useful.

Anyhow, thanks for all the tips.

What I think I will do is build a small box out of MDF to represent all the various surfaces and edges my cabinets will have. That I will test these various different techniques and see what works best for my situation.

I'll keep this updated on my progress....

 

[Ukwoody]

Would be interested to hear the results!
Woody

 

[dbbyleo]

Well woody, the results are in.....

I built a small replica of a my cabinet. I used only MDF and even ripped 1x2s to make for the fascia. Obviously, I has a lot of exposed MDF edges. On one-third of the unit, I used PVA glue to seal the edges. On one-third on the unit, I used wood filler. And on the last third, nothing!.

After applying the above, I sanded a little to get a smooth finish.

Then I applied 2 coats of primer (Brand: Behr, water-based).

Frankly, I the only difference I found was in the smoothness of the exposed edges. Where I applied wood-filler, it was baby-smooth. A little less smooth was where I applied PVA glue. Where I applied no treatment, well... it was as rough as exposed MDF is.

As far as the wood soaking up the primer and expanding, I saw none - even in the area where no treatment was applied.

I suppose using decorative caulk would have the same results as wood-filler, except it would probably spread easier.

I'm left to give it a top coat (using Behr Sateen Enamel). I don't suppose I'll see in difference in the way the MDF will react since the primer/sealer has already been applied.

All in all, it's turning out is well.