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post #1 of 22 Old 05-26-2014, 01:35 AM Thread Starter
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Help with finishing MDF?

After i get my cuts done from MDF board for my desk, i want to paint them, them seal them. Thing is, i dont know what to seal them with. I want to make them water resistant for the most part, and add a slight shine. So, a clear coat would be what i am wanting, right? Please correct me if im wrong. Now, im thinking a clear Polyurethane coating, or lacquer... (both oil based obviously since MDF) would these be good options for a clear coat sealing finish? Please let me know if there are other, better options, or what would be bad about these choices. So, would those options for a sealant and clear coat finish be good? I also dont want to spend much... maybe $15 for a bucket of whatever size of the stuff, tight budget, i know. It should also be known that ive never really worked with wood, let alone finishing wood and such, so it would be better to not have an overly complicated process, but i am okay with sanding and waiting, it would just suck to have to wait hours for a coat to dry and have to sand and coat again, but thats me rambling. Anyways, any help here, please? Thank you in advance.
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post #2 of 22 Old 05-26-2014, 07:16 AM
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Seems to me this is 2 questions, and the part about being water resistant (and sealed) will be solved by the paint (if it's a good paint). Using a good oil based primer, topped by whatever oil based or 100% acrylic (water borne) paint will be incredibly durable; at least as much as any clear coat you could use. But it seems to me you also want to make the cut areas as smooth as possible to match the slick surface of the MDF (second question, maybe unasked). Cut edges of MDF are sealed by a lot of stuff, spackle compound, drywall mud, several good coats of an oil based primer, or glue size. The glue size is what I normally use, mix regular yellow glue about 4 parts water to 1 part glue and apply it with a rag, brush, whatever, at least twice. Then sand it smooth.

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post #3 of 22 Old 05-26-2014, 08:33 AM
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I always had trouble finishing MDF. It's pressed into a sheet and the outer surface of the sheet has a high amount of formaldahyde on it. This chemical affects the finish you are trying to put over it so I always sand the MDF prior to finishing. It doesn't take a great deal of sanding, just enought to cut the glaze.

First of all lacquer is much different than polyurethane and the two should not be used together. Polyurethane doesn't bond well to lacquer and lacquer is so hot it damages most any oil base product.

You actually have it backwards, you seal first and then topcoat. If you wish to use an oil based paint I would first seal the wood with a shellac based white primer. There is usually defects you don't see until you start priming so keep priming and sanding until you get the substrate as good as you can before topcoating. The edges you can espect to take several extra coats as MDF really drinks up the finish. If it were me I would slect a paint which has the sheen you desire rather than clear coating it afterwards. Clear coats often peal off or tend to yellow changing the appearance. If you are intent on clear coating I would finish the desk with a wall and trim latex paint and then topcoat with a water based polyurethane. The water based poly would remain clear.

If you wish to finish with lacquer I would use Bushwacker white lacquer primer sold by Sherwin Williams. Like anything else it will take multiple coats on the edges. Put as many coats as it takes to get the substrate smooth and level sanding between coats with 220 sandpaper. Then the desk could be sprayed with a production lacquer. Sherwin Williams sells production lacquer but it's something you probably will have to order. Most stores cater to common house paint rather than an industrial product like lacquer. You can clear coat over lacquer. You could use a pre-catalyzed lacquer or a cab-acrylic lacquer to topcoat with. Each would bond and remain clear.

The lacquer would be the quickest and easiest finish you could use however the oil based enamel would be the best finish you could use.
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post #4 of 22 Old 05-26-2014, 09:41 AM
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Waterbased polyurethane finishes off MDF nicely. You don't need a sealer. Edges will seal up, and it's easy to sand.






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post #5 of 22 Old 05-26-2014, 09:43 AM
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As Steve said, Seal and then topcoat with paint. The sanding sealer needs to be compatible with what you plant to use for the topcoat. Be sure to sand the sealer with fine grit paper before applying the topcoat. You can use polyurethane automotive type paint to give a durable finish if you have a spray rig. For a really high gloss, you can apply a clear topcoat which can include either poly or lacquer on top of poly once it has cured. Just be sure to never do the opposite which is applying poly on top of lacquer.

BTW, I don't think that MDF can actually be made water resistant. If this is something that will be used where it comes into contact with water regularly, it will eventually swell like a sponge. I would only consider using MDF in hidden areas of a desk or cabinet. Besides that, working with MDF is nasty.

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post #6 of 22 Old 05-26-2014, 04:24 PM
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You can apply wood "peel & stick" or "iron-on" veneer edge-banding, maple works well for paint, to the cut edges.
This will give you as good a finish on first coat as you get on the flat sides that are factory sealed.
Laminate file then sandpaper works well for flushing edges up.
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post #7 of 22 Old 05-26-2014, 06:17 PM Thread Starter
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Quote:
Originally Posted by bzguy View Post
You can apply wood "peel & stick" or "iron-on" veneer edge-banding, maple works well for paint, to the cut edges.
This will give you as good a finish on first coat as you get on the flat sides that are factory sealed.
Laminate file then sandpaper works well for flushing edges up.
I was going to use wood veneer for a nice wood grain and sold wood look, but its too expensive. I would need 2 4*8 sheets of the stuff and that would be like $60 i found out, then i would stain it or something. But now i just decided it would be cheaper to just paint the MDF as something light brown to mimic the color of the wood grain i wanted.
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post #8 of 22 Old 05-26-2014, 06:44 PM Thread Starter
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Thanks for all the help and replies guys!

So it seems now that i should seal and paint. Okay, so what would be the cheapest and most efficient(quick and simple) way to seal the MDF faces, and edges? Would just a basic white, oil based primer paint be good enough? Or do i need some extra stuff or something else? What kind of sandpaper should i use? Steve said 220, is that correct to use? How many coats should i apply and how long would it take to dry between coats before i sand and re-coat... considering i leave it outside with no moisture or anything? Also, when its time to apply the topcoat paint, should i sand it between coats too orrrr?
@Steve Neul: You said "lacquer is so hot it damages most any oil base product." I thought it was like a paint you just roll or brush on? What do you mean its hot? Do you have to heat it up first?

Another part of a question. I dont want a gloss finish or anything, i just want a slight sheen, but not a sticky feeling like some paint finishes do, i think satin or eggshell has this feeling, like some painted walls have this slight sticky or thick feeling when you touch it... eww. Anyways, so i dont need a clear coat like polyurethane as long as i use a primer to seal and a topcoat of paint? If so, then what is the point of lacquer or polyurethane on top of paint... would it be just for a high gloss finish or for total waterproofing orrr what? So i guess i dont need a clear coat on top after all?
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post #9 of 22 Old 05-26-2014, 06:51 PM
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Quote:
Originally Posted by DarkDubzs View Post
I was going to use wood veneer for a nice wood grain and sold wood look, but its too expensive. I would need 2 4*8 sheets of the stuff and that would be like $60 i found out, then i would stain it or something. But now i just decided it would be cheaper to just paint the MDF as something light brown to mimic the color of the wood grain i wanted.
The thin rolls of edge-banding just save you a lot of sanding and painting the 5/8" or 3/4" edges that inevitably swell, get rough and need to be sanded over between coats when painted.
By doing this I save a lot of time and use a lot less paint.
I usually use lacquer and spray the entire surface every coat.
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post #10 of 22 Old 05-27-2014, 07:28 AM
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A good oil based or 100% acrylic paint will not have that sticky touch to which you refer, that is normally what happens when a latex paint is used (like a wall paint). So a good primer (they are mostly white, but m,any can be tinted if you plan to topcoat with a dark color) followed by the paint. There is (IMHO) absolutely no reason to put a clear coat on top of good paint....and a lot of reasons not too.

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post #11 of 22 Old 05-27-2014, 08:56 AM
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Quote:
Originally Posted by DarkDubzs View Post
Thanks for all the help and replies guys!

So it seems now that i should seal and paint. Okay, so what would be the cheapest and most efficient(quick and simple) way to seal the MDF faces, and edges? Would just a basic white, oil based primer paint be good enough? Or do i need some extra stuff or something else? What kind of sandpaper should i use? Steve said 220, is that correct to use? How many coats should i apply and how long would it take to dry between coats before i sand and re-coat... considering i leave it outside with no moisture or anything? Also, when its time to apply the topcoat paint, should i sand it between coats too orrrr?
@Steve Neul: You said "lacquer is so hot it damages most any oil base product." I thought it was like a paint you just roll or brush on? What do you mean its hot? Do you have to heat it up first?

Another part of a question. I dont want a gloss finish or anything, i just want a slight sheen, but not a sticky feeling like some paint finishes do, i think satin or eggshell has this feeling, like some painted walls have this slight sticky or thick feeling when you touch it... eww. Anyways, so i dont need a clear coat like polyurethane as long as i use a primer to seal and a topcoat of paint? If so, then what is the point of lacquer or polyurethane on top of paint... would it be just for a high gloss finish or for total waterproofing orrr what? So i guess i dont need a clear coat on top after all?
220 grit is about the coarsest sandpaper you can sand between coats and not show scratches when you coat over it.

What I meant about lacquer being hot is it contains acetone in the lacquer thinner it is thinned with. For example if you finish a project with an oil based enamel and then put lacquer over the top of it the solvents in the lacquer would eat into the paint and wrinkle it up like you put paint and varnish remover on it. Lacquer because it dries so fast isn't practical to brush or wipe on, its better sprayed. They do make brushing lacquers but those have solvents that slow down the drying time enough to brush. They still don't brush as good or easy as oil based finishes. They work more like shellac. You could put the first coat on easy but the second coat melts into the first coat so you have to move fast laying it on or you end up removing the first coat and it gets worse with consecutive coats.

In my opinion if you are going to paint use paint only and not put any clear finish over the top. The only time I put a clear coat over paint is when I paint a car with a metalic paint. Then I use a basecoat/clearcoat system of finishing. Solid colors on a car I don't clearcoat. For cabinets and furniture paint comes in a multitude of sheens you can finish with. The glossier you use will be more durable as the flattening agents in the paint make the surface more porous.
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post #12 of 22 Old 05-27-2014, 09:04 AM
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Quote:
Originally Posted by Fred Hargis View Post
A good oil based or 100% acrylic paint will not have that sticky touch to which you refer, that is normally what happens when a latex paint is used (like a wall paint). So a good primer (they are mostly white, but m,any can be tinted if you plan to topcoat with a dark color) followed by the paint. There is (IMHO) absolutely no reason to put a clear coat on top of good paint....and a lot of reasons not too.
+1. Just adding, that a sufficient dry time (to allow a FULLY cured, not just a cured) finish will help with the blocking problem. I added the FULLY just for the drama.






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post #13 of 22 Old 05-27-2014, 09:26 AM
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Elmer's glue thinned with water and using fiberglas resin are the two ways I've used!
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post #14 of 22 Old 05-27-2014, 10:33 AM
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Maybe its just me, but I don't think a desk surface is a good place to use a latex paint, even if it is 100% acrylic. I've used latex from home depot, Sherman Williams, etc, and they were all 100% acrylic, but I feel like they took a long time to fully cure. The last thing I painted with acrylic was a year ago, and the doors still stick slightly to the cabinet. This was semi-gloss though. I prefer oil based for anything other than walls now.
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post #15 of 22 Old 05-27-2014, 01:09 PM
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Latex paint is a general term which covers all paints that use synthetic polymers such as acrylic, vinyl acrylic (PVA), styrene acrylic, etc. as binders. The term "latex" is applied to most water-based paints, regardless whether the can says they are 100% acrylic, latex or vinyl styrene. A paint with a high acrylic content will have much better water and stain resistance, but you can't tell the acrylic content by looking at the can, nor can you tell by looking at the MSDS.

Primers are generally recommended for use over bare wood. Use a primer that is compatible with the topcoat. Before applying anything, sand the MDF perfectly smooth. This generally means that you need to sand the edges as the flat part is already smooth. Sand up to 400 grit or at least 320. The flat parts need only a light brushing with 400 grit, but the edges might need more. Thoroughly vacuum away all of the dust and then use compressed air.

I recommend a clear varnish sanding sealer as a primer. There will be some slight fuzz up from the wood/MDF so just a light amount of sanding with 400 grit ought to take care of that. Sanding the sealer/primer will create some dust so clean the surface as before prior to applying the topcoat. I recommend using either urethane or, even better, polyurethane paint as the topcoat. It is far more durable and water resistant than anything else. Unfortunately, it is also more expensive. You need to go to a real paint store to find it as most hardware stores, including the big box stores, are not likely to have it. Do not sand between coats. There is no need and it will only add scratches. Polyurethane cures slowly by polymer crosslinking. The surface is dry in a few hours, but underneath, it take at least a week to reach full toughness. Polyurethane is used on everything from wood floors to aircraft -- wherever a durable finish is needed. You can get high gloss, semi gloss, and possibly satin finishes, but definitely not flat. Urethanes probably have a wider range of surface sheen and cost less than the polyurethanes.

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Last edited by Bill Boehme; 05-27-2014 at 01:12 PM.
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post #16 of 22 Old 05-28-2014, 11:29 PM Thread Starter
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How can i get a slight shine exactly like is seen on the wood of the desk in the beginning of this video? I wanted a desk just like that in terms of looks, but a bit longer and with the legs and shelves like you may find in my other threads. Well now i just have to paint it, so what finish would get me a nice shine just like that? thats why i started this question in the first place, i thought i would need a clear coat like polyurethane or something to get a slight shine like this, so do i after all or what oil based paint finish would i need to achieve this exact kind of shine as seen in the following video? Semi-gloss, satin, eggshell??

Also, do you guys think thats a block of solid real wood or MDF as well? If its mdf or plywood, that is a perfect looking veneer!! Perfect color that i wanted, perfect shine, perfect shape. Goddamn. I guess i could always add a layer of veneer or stick some vinyl on when i get more money... idk.

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post #17 of 22 Old 05-28-2014, 11:40 PM Thread Starter
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Also, just to clear up some confusion, i dont plan on using latex paint, based on your guys' comments that it is the type of paint i said i did not want, the type that feels sticky and thick and literally sticks to stuff sometimes... like whiskeypete said "the doors still stick slightly to the cabinet" and this is true as ive seen with some doors and cabinets, etc in old houses and places... i hate that feeling and how it is, so no latex paint for me then. Make sure to please help me out with my reply above, please.
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post #18 of 22 Old 05-28-2014, 11:46 PM Thread Starter
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*Just leaving this here for reference*
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post #19 of 22 Old 05-29-2014, 11:33 AM
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I haven't tried this out myself myself but I've read about using flat latex tinted to the color you want then top coating with poly. From what I understand, flat paint cures a lot faster that those with a shine and the you can topcoat with poly to get the protection you need and the sheen you want without being sticky. I'd just be guessing, but in that video i think it looks like semigloss to me. Google "poly over latex" and you find a bunch of advice. I've never painted MDF so I don't know how it reacts, but I hope this helps.

Also, as Bill Boehme said, alot of paints fall under the catagory of "latex". I would ignore advice from those that think latex paint contains latex.

Last edited by whiskeypete; 05-29-2014 at 12:15 PM.
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post #20 of 22 Old 05-29-2014, 08:04 PM Thread Starter
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I haven't tried this out myself myself but I've read about using flat latex tinted to the color you want then top coating with poly. From what I understand, flat paint cures a lot faster that those with a shine and the you can topcoat with poly to get the protection you need and the sheen you want without being sticky. I'd just be guessing, but in that video i think it looks like semigloss to me. Google "poly over latex" and you find a bunch of advice. I've never painted MDF so I don't know how it reacts, but I hope this helps.

Also, as Bill Boehme said, alot of paints fall under the catagory of "latex". I would ignore advice from those that think latex paint contains latex.
That sounds like it might work, but if i can get the same effect with just paint, id rather just use paint since my budget is small and it would be easier anyways.

.......
After a bit of research just now, im kinda leaning towards semi-gloss oil pant now instead of eggshell. Reason being, i want almost like a hard shell kind of feel and look that you get with gloss paint and gloss stains/clearcoats, but i dont want the super shiny look and reflection... i want a slight shine. I guess i dont really know right now since i havent even seen the finishes in person, only google images, so next time or when i go buy the wood and paint, etc. ill make sure to take a good look at the paint finishes and feel them, but i think semi-gloss is what ill go with. If im not satisfied with what finish ill get based on sample splotches display, or for whatever reason, ill ask questions.

Looking at pictures online like these: LINK i really wish i could have a wood grain look on my future desk surfaces, even a wood floor look that doesn't have a continuous grain like in those pictures. Ive been thinking, maybe i can buy a few square feet or however much i need of wood flooring laminate or something, shouldnt be too expensive since its only like less than a dollar per square foot? And somehow i can mount it to the tops and sides of the mdf?

What do you guys think about this idea and everything else i covered here? Please help guys, thanks!
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