[fraseyboy]

So I want to make a desk.

I've got a big sheet of MDF that I want to paint. I presume I have to use some sort of undercoat/primer first? There's some general-purpose wood primer in the garage... Would it be ok to use that?

Thanks.

 

[Uncle Erik]

If the surface of the MDF isn't perfectly smooth, fill it with a thin coat of Bondo, then sand it smooth. After that, follow with several coats of primer meant for whatever kind of paint you'll use.

 

[fraseyboy]

Well the surface is pretty damn smooth. Don't think it needs sanding or anything.

I've got some all-purpose interior/exterior primer here which says it works with the type of paint I've got. So I just use that? Is any sort of roller to apply it ok?

 

[Listen2this1]

Yes the MDF feels smooth but there can be high spots adding a layer of body filler or heavy build primer gives you a chance to see the high spots and the low spots after sanding. There is always some. You really need to pay attention to the edges, they can absorb paint very well, so I usually start with them then move onto the flat area. If the primer is done well the finish that can be achieved is very good. Also you need to think about the amount of abuse the finish will get. Some finishes are not designed to have abuse, so use a better quality paint, maybe from a automotive paint store and not Home Depot.

 

[fraseyboy]

Quote:

Originally Posted by Listen2this1 /img/forum/go_quote.gif Yes the MDF feels smooth but there can be high spots adding a layer of body filler or heavy build primer gives you a chance to see the high spots and the low spots after sanding. There is always some. You really need to pay attention to the edges, they can absorb paint very well, so I usually start with them then move onto the flat area. If the primer is done well the finish that can be achieved is very good. Also you need to think about the amount of abuse the finish will get. Some finishes are not designed to have abuse, so use a better quality paint, maybe from a automotive paint store and not Home Depot.

Hmm ok... Well I use some Pollyfilla on all the edges, which I will then sand down and use the undercoat primer on them. I don't think I need to use the pollyfilla on the top and bottom. I'll just use the undercoat on them.

I won't be abusing it THAT much. It's just a desk. I'll be putting paper on it and writing on that, typing on it, etc.

 

[DocHamm]

Apply sanding sealer to the MDF to "seal" the pores of the surface. This prevents paint or varnish from soaking into the MDF which causes a very "patchy" surface if you try to paint it directly.

Whatever you do, seal the surface with sanding sealer. When it is dry, sand back and re-apply till it is as smooth as your standards dictate. Once you have a sealed, flat and scratch free surface, you can then paint it.

I understand that your MDF boards have a nice surface finish, meaning they are smooth and have no scratches and are flat. The problem is with MDF (and all chipboard) is that it is porous. It's surface will absorb liquids, moisture, dirt and small fine particles. Sanding sealer goes into the pores and effectively blocks them. Thus when you apply your varnish or paint, it will not be soaked up like a sponge.

Soaking on its own is not the problem. If it soaked up a bit of varnish or paint, you just apply a few extra coats. Where the problem lies is that on large surfaces, the porosity varies from area to area. Thus you get a "patchy" finish if you apply your paint or varnish direct.

Sanding sealer is available at any local woodworking or paint supply store. I prefer Deft brand which I get locally at Woodcraft.

 

[Uncle Erik]

What kind of paint are you planning to use? Desks are high traffic areas - something like an ordinary household latex will not hold up. Just resting your arms on it for a couple of months will show wear.

I'll second the call for automotive paint. It holds up much better. That, or use something oil based.

Another option you might want to consider is painting it, then dropping a piece of glass on top. Glass is surprisingly cheap - you'd be surprised at the prices. Some varieties are a dollar or two per square foot and the glass shop will cut it for you. The trick is getting it back home if it's big, but the shop might deliver. That would make a nice desktop - one you can put drinks and food on. The paint will stay nice (even latex) and it'll clean up easily. You could also do cool stuff like put photos, artwork, papers, etc., under the glass.

 

[fraseyboy]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif What kind of paint are you planning to use? Desks are high traffic areas - something like an ordinary household latex will not hold up. Just resting your arms on it for a couple of months will show wear. I'll second the call for automotive paint. It holds up much better. That, or use something oil based. Another option you might want to consider is painting it, then dropping a piece of glass on top. Glass is surprisingly cheap - you'd be surprised at the prices. Some varieties are a dollar or two per square foot and the glass shop will cut it for you. The trick is getting it back home if it's big, but the shop might deliver. That would make a nice desktop - one you can put drinks and food on. The paint will stay nice (even latex) and it'll clean up easily. You could also do cool stuff like put photos, artwork, papers, etc., under the glass.

The paint is standard semi-gloss water-based enamel.

Already bought it though, at quite an expensive, so unless they allow returns... That glass idea sounds intriguing. If it is easy and cheap to acquire a piece of glass like that then that'd probably be best. Hopefully it doesn't make it too heavy. It's held up by two legs at equal distances from each side in the centre, and braces on the wall.

Also, since it's a pretty big peice of wood, would it be ok to sand it using an orbital sander or do I have to do it by hand?

 

[DocHamm]

Orbital or belt or hand ... anything is fine, just keep it even.

A couple of my little lathe woodturning projects ...



I painted my Beech desk black, stained the top cherry and sealed the top with poylurethane. The top is what will take the abuse, so in my case I used three coats of poly to give it a liquid looking finish that won't get water damage (rings, spills etc.) and hold up to daily use.

 

[fraseyboy]

Quote:

Originally Posted by DocHamm /img/forum/go_quote.gif Apply sanding sealer to the MDF to "seal" the pores of the surface. This prevents paint or varnish from soaking into the MDF which causes a very "patchy" surface if you try to paint it directly. .

What is the difference between 'sanding sealer' and 'acrylic sealer undercoat'?

 

[DocHamm]

Quote:

Originally Posted by fraseyboy /img/forum/go_quote.gif What is the difference between 'sanding sealer' and 'acrylic sealer undercoat'?

Sanding sealer is a clear primer especially made for sealing wood and is very popular with woodworkers, especially furniture makers. It fills pores and has low dust properties.

Acrylic sealer/undercoat is generally used more on masonry, plaster wallboard, fibro and suitably primed timber and metal surfaces.

Deft is made specifically for wood, ergo it's being more effective and popular on wood surfaces and not masonry, plaster, etc.

Drying times may vary, coat requirements may vary and sanding may vary and some are more expensive.

Not sure what brand you bought, but if you read the label and follow the directions it should be fine.

Up to you how much elbow grease you want to put into it, but a little goes a long way. Hope it comes out just the way you want.

 

[rsaavedra]

Pics!!!!

 

[DocHamm]

Have you finished it yet? How did it come out?? Pictures?!?!

 

[J.D.N]

I'm half way through a Flexi Rack build using MDF and personally i've started with three coats of MDF Sealer. Rubbing down in between each coat. If you have a lot of edges visible its a must as MDF just soaks up pain like no tomorrow. You will also notice that edges get quite rough after you paint them so they need constantly rubbing down with each coat.

Then as above, use high build primer. If you put it in a sink of just-over-warm water it becomes slightly thinner and easier to apply the first 2-3 coats. You really want lots of thin coats rather than fewer thicker coats as the paint will dry and contract if you aren't careful. Then follow with a few coats of high build without thinning it.

During all this you want to be moving up the grades of sand paper. Start at around 300 then move to 600/800. When you are applying the final colour coats you want to end up on about 1200/1400 grit maybe even some wet/dry depending on the finish you are going for. It might 'feel' smooth now, but once you've put 15-20 coats of various paints on and sanded them down with the higher grit papers, you will start to realise just what smooth feels like!

Just my 2p.

Cheers

 

[fraseyboy]

Yes, I've finished it. I did two coats of acrylic sealer undercoat and three coats of water based paint. It came out very nicely and has a nice texture. It looks like it will hold up for a while.

Here's a photo of the desk in place which I also posted in the 'post pics of your headphone setup and listening area' thread.