How to paint MDF?

[Chimaera]

Hi folks,

I'm completely new to woodworking so please excuse my confused newbie type questions here.

Alright, so basically I'm building a desk. It's a fairly simple design, 700mm wide and running the length of the room at 2800mm with a small 400x450mm section sticking out at one end to form an 'L' shaped bench. I'll be cutting it from a single sheet of 18mm thick MDF from my local Bunnings with a welded steel frame for the legs and support.

My questions are mostly related to sealing, priming and painting the MDF board. I've been reading a bunch of information on the net to that extent and it's resulted in a huge amount of confusion on my part from the sheer number of different (and often contradictory) opinions.

So firstly, sealing and priming. I've read differing opinions about this, from people saying that you don't need to seal it, just paint and sand between the coats to advocates of any number of sealing methods. Then there's whether the sealer should be an oil- or water-based product, again I've read so much contradictory information it's ridiculous.

First lot of questions:


What products can people recommend for sealing and priming the MDF?
Should it be water-based or oil-based? Why / why not?
I've found a product at my local Bunnings which is an MDF Primer from White Knight (water-based, I believe) that is supposed to seal and prime the MDF, has anyone had experience with this product? Did they get a good result from it?


Then there's the issue of painting. Again, I've read that many different opinions and product options that my head is likely to implode (yes, I'm exagerating just a tad :) ). I'd like to get a fairly smooth finish on the desk with a bit of gloss to it. I'm fairly new to painting also, the extent of my experience so far being painting the walls and window/door frames of my house.

Second lot of questions:


What product or type of paint can you recommend for a semi-gloss finish on the desk?
Will I need a clear topcoat to prevent the surface being "tacky" or to add some extra protection/durability to the finish? If so, what product can you recommend?
Can I get a decent finish using a roller? And what sort of roller and method would you recommend for a smooth finish?
Would I be better off spraying the desk instead? If so, can someone recommend an affordable paint sprayer (I'm a poor uni student after all)?

And I think that's about all my questions, apologies again for how many there are. If anyone can help a confused girl out I'd really appreciate it.

~Sam

[Sturdee]

I presume the desk is for a home office/study area/computer workstation. If so, I would not paint it but instead I would cover the surface by glueing on a vinyl top.

It can be the standard type of floor vinyl or even the larger vinyl self stick floor tiles and the edge finished with a clear laquer finished timber batten. This also helps to hide slightly imperfect cutting.:D


Peter.

[Manuka Jock]

Chimaera ,
Best to seal the cut edges , seeing as they are 'end grain' so to speak .
Use bog on any joins , cracks , nail and screw holes etc .

Use enamel paint ,
with the required preparation and undercoats
Spray it it possible , if not brush it on properly , in the manner that enamel paints require .
Follow the instructions to the letter .


Do not use acrylic paint .
Do not use a roller .

Good luck ,
Jock

[jatt]

I guess the first question I would ask is are u trying to hide the fact that it is a MDF top? This will help u decide upon which finish to use.

We have large (approx 6000 x 2400) MDF topped tables that are used primarily as sewing tables for industrial sewing machines.

All we used is Cabotane applied over raw MDF . I cant imagine what I would have to assume is a standard desk, in your case, copping the abuse these tables are put thru. The stuff seems to stand up to this environment quite well.

All of the raw edges were coated in the same manner.

The smell whilst the stuff is drying is quite intense, then again most of the clear finishes I have come across are.

Simple enough to do.

[Chimaera]

Thanks for the responses and suggestions. I was planning on painting it purely for aesthetic reasons. After trawling through the forums here for a few hours searching for mentions of MDF, painting, etc., I've decided on the following process:

- Sealing the edges with a mix of PVA glue and water (4:1) and then sanding that back to smoothness
- Sealing and priming with White Knight MDF Primer
- Spraying with an enamel gloss paint (after begging and borrowing a spray gun). It's a water based enamel solely for drying time reasons, I don't have anywhere I can leave something this big to dry that wouldn't result in it having a multitude of dust and cat hair sticking to it.

Obviously I'll be sanding between all coats and I've bought some sheets of sandpaper from 180 through to 1000 grit for this purpose. Hoping to work up to a decent gloss on the desk. I found a post on here from someone who got a fantastic gloss finish with this sort of process and polishing with a rubbing compound (which I'll have to look into more).

Thankfully there won't be any visible joins, nails, screws or any other form of connection. The steel frame will be connected from underneath and the rest is pretty well a solid piece.

I've got all the cutting and initial edge sanding out of the way today, so it's on to using the router to curve the top edge and then sealing them up tomorrow morning.

It'll hopefully stand up to a fair bit of abuse. Studying photography so there'll be equipment up and down, mounting prints and various other art and sculpture projects on the go.

I'll see about posting some pics and letting you know how it goes.

[Bazzmate]

If you are painting it, will will need to seal it first. I use British Paints 'All in One' primer/sealer on MDF before doing a top coat. The people in the big green shed will sell you some. I guess you could do a few spray coats to fill the cut 'end grain' but I just paint the edges to fill the 'end grain' and then sand them smooth before spraying the lot. It' s a bit extra work but gives a better finish. As I am only doing small piecework in mostly 6mm thick MDF, my topcoats are from $3 cans of Supacheap spraypaint. They give a great finish but probably not good for benchtops?
I built a desk once for a friend and the top coat she used was a water based gloss red enamel. It gave a pretty good finished appearance and I didn't hear any complaints about it regarding wear and tear either. Hope that helps.

[Papa]

For a desk or table top, painting would be my last choice.
I finish desks and table tops with laminate flooring, cheap
and easy. Will stand up to most any thing.

I get the laminate from the bargain table at Lowes, when
they haves some I pick up some for stock. A pack does
fourteen sqr. ft. and costs around $10

I use construction adhisive to put it down and add a nice wood
edge after I use a laminate bit to trim it flush.

Like this:

[Chimaera]

Thanks again for the various suggestions and advice. I've already bought the paint and I'm a very poor uni student who can't afford to get anything else, so the laminate and vinyl suggestions will unfortunately have to be shelved for another project. Perhaps I'm silly, but I liked the idea of a deep red desk so I've got myself a gloss Dulux Aquanamel.

I've sanded and routered (bevelled?) the edges and applied a coat of 5:1 PVA + water to seal the edges as you can see in the images below.

So tomorrow morning I'll be sanding back all that raised grain you can see in the corner detail. Then on to the MDF primer.

[witch1]

chimaera,
I guess I'm too late, but for future reference I have found, after trying everything else that the ultimate sealer-undercoat for MDF, particularly after routing edges is ZINSSER shellac based sealer-undercoat it is easy to apply easy to sand, touch dry in 15 minutes ready to sand after about an hour and accepts a top coat beautifully.
regards
witch1