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Old 2nd July 2002, 08:35 PM   #11
Schaef is offline Schaef  United States
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Okay, slight confession here, I've not painted MDF yet, I'm giving advice based on information I have read here and in woodworking bulletin boards, so I have no personal experience with painting MDF. Having said that, my finishing experience is tied to my woodworking projects. (right now, a small table/desk for a second computer made from maple, finished with a tung oil mixture and top-coated with poly, already looking real good with only two coats of oil!)

As to which paint is better, that's hard to say, partly because I'm not sure if you want a name brand, or if you're looking at oil vs. water based. I can't help a lot there, as my finishes have mostly been of the oil or shellac or poly variety. I will say that with current technologies, the differences that once existed between the paints are getting smaller and smaller. However, one piece of advice I CAN give, is to not skimp on the quality of the paint. Based on the size of the speakers, (you are building just two, right?) a gallon of paint should be more than enough.

As to spray versus brush, if you can spray and know how, it should produce a smoother finish. (I'm talking HVLP gun, compressor and what not here, not spray cans) If you take your time with a quality brush though, you should be able to get a really nice finish with a brush as well, it'll just take a little more work.

As to sanding, you just want to sand enough to make the surface smooth again. It should feel pretty smooth before you rub/sand it, but afterward, you won't believe the difference! One other key item, is to put on thin coats, don't try to do a one coat coverage, it'll look like it. Do multiple thin coats, it'll come out smoother and look better.

As to the shine, you can do a couple of things, and here, you should experiment a little with some scraps. (Just finish a couple scraps along with the main piece, so you can try these things) This will help you decide what looks best to you. When you get to the final step, you want rub out the final coat with the steel wool, then switch to a very fine grit sand paper (600+), and then you can try going further with using rottenstone paste and a rag. Alternatives to the last step include using car wax and buffing it out. (It can look quite nice and if you have a power buffer, it can look even nicer) Basically you want to polish the finish for the last step, this will give you the high gloss you want. (In addition to using a gloss paint to begin with)

Hope this helps you out!
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Old 2nd July 2002, 11:10 PM   #12
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Hi Mike

Well, I have some experience with mdf, (real wood is so very expensive in the UK), so I might be able to help.

The main problem with mdf finishing is getting a good base, as the plane surface can cause primers and paints to pinhole due to the mixture of woods and resins used.

The endgrain is also very very absorbant, and will suck up paint like there is no tomorrow!

The only way I ever achieved a good piano black finish on mdf was very time consuming, but was done as follows;

1) round over any sharp edges with a router or power sander

2) sand, sand, sand, and then sand some more

3) fill all construction screwholes and minor gaps, as well as running a thin layer over any exposed engrain, with 2 part car body filler

4) sand some more, and then wipe down with thinners

5) spray on a couple of thin coats of car body primer

6)lightly sand, and then fill in any new holes/ marks that you can now see with more filler

7) spray on more primer in thin coats, lightly rubbing down with very fine wet and dry paper between coats, until you can no longer see the difference where the endgrain starts and the face material. When you do this, use a sanding block and warm slightly soapy water, then wipe with a slightly damp cloth and allow to dry fully.

8) when satisfied you have a flat finish, apply 4 or 5 coats of colour, knocking the finish back as above between coats.

9)apply 3 or 4 coats of laquer ( making sure you use the same paint maker as your body coat, as some paints can react), knocking back as above

10) allow to dry for a minimum of two weeks

11) very lightly sand, as above, for one last time

12) polish using firstly a cutting compound such as T Cut, and then buffing with wax by hand, as many times as you like...


This is why I now veneer all my mdf boxes!
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Old 2nd July 2002, 11:22 PM   #13
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Hi Mike

Well, I have some experience with mdf, (real wood is so very expensive in the UK), so I might be able to help.

The main problem with mdf finishing is getting a good base, as the plane surface can cause primers and paints to pinhole due to the mixture of woods and resins used.

The endgrain is also very very absorbant, and will suck up paint like there is no tomorrow!

The only way I ever achieved a good piano black finish on mdf was very time consuming, but was done as follows;

1) round over any sharp edges with a router or power sander

2) sand, sand, sand, and then sand some more

3) fill all construction screwholes and minor gaps, as well as running a thin layer over any exposed engrain, with 2 part car body filler

4) sand some more, and then wipe down with thinners

5) spray on a couple of thin coats of car body primer

6)lightly sand, and then fill in any new holes/ marks that you can now see with more filler

7) spray on more primer in thin coats, lightly rubbing down with very fine wet and dry paper between coats, until you can no longer see the difference where the endgrain starts and the face material. When you do this, use a sanding block and warm slightly soapy water, then wipe with a slightly damp cloth and allow to dry fully.

8) when satisfied you have a flat finish, apply 4 or 5 coats of colour, knocking the finish back as above between coats.

9)apply 3 or 4 coats of laquer ( making sure you use the same paint maker as your body coat, as some paints can react), knocking back as above

10) allow to dry for a minimum of two weeks

11) very lightly sand, as above, for one last time

12) polish using firstly a cutting compound such as T Cut, and then buffing with wax by hand, as many times as you like...


This is why I now veneer all my mdf boxes!
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Old 3rd July 2002, 02:33 AM   #14
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Thanks for the great advice on the painting guys. I think instead of the high gloss finish, ill try for more of a semi-shiny finish Im just going after a smooth nice looking black here, so even flat would probably work. Thanks once again guys, gonna start ordering all the pieces for this here in a couple days Regards

Mike
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Old 3rd July 2002, 10:02 AM   #15
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you could try using ply and black stain, that might look good as a finish, and it would be a lot easier than painting.
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Old 3rd July 2002, 09:56 PM   #16
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by ply, do you mean like a laminate or a vaneer? Thanks

Mike
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Old 3rd July 2002, 10:41 PM   #17
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Just remember to wear some breathing protection cutting the MDF. It's pretty nasty stuff, but even a simple paper mask should help.
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Old 3rd July 2002, 10:57 PM   #18
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Just ordinary furniture grade plywood Mike.

And I definately agree about wearing a mask, and eye protection too if using powertools.
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Old 4th July 2002, 02:48 AM   #19
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ook, plywood, im sorta new to the lingo My only concern with plywood is its rigidity as a building material, as compared to MDF, also, does it come in 3/4" sheets? Oh yeah, eye protection is a must, and as for the facial mask, i didnt know MDF was that harsh, thanks for the heads up . Thanks for all the help.

Mike
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Old 4th July 2002, 05:07 AM   #20
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Just want to second the comment before about the use of masks when cutting mdf, the glue in that stuff is pretty nasty, and the dust from it is so much finer than wood dust.

Plywood definetly comes in 3/4 thichness, as well as 1/2 inch, and 1/4 inch. As for it's rigidity, I guess that kind of depends what you mean. Is it as dense as mdf, no not at all. Now this part is just my thoughts, the ideas are fact, but might not translate to reality in this case. So here goes, Plywood is made of thin sheets, obviously each known as a ply, which are glued together under pressure to create the final product. Now these plies are normally glued together with each layer's grain going perpendicular to the last layer's grain. This is intended to increase what I would call rigidity over regular wood in which the grain goes all in one direction. The reason I mention this is because to me working with plywood is much preferable to working with mdf because I feel it is worked much easier. Meaning it isn't as rough on my table saw blades, it doesn't have as nasty a dust, it takes screws well, it can be finished nicely, etc. So my thought would be if mdf isn't much more rigid than plywood, then plywood might be the material of choice for easiest construction.

Thoughts??

Mark
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