HOW TO OBTAIN AN EVEN, "mirror like" SURFACE ON PAINTED MDF

[yorkincr]

I want help in getting an even surface when you paint MDF furniture. We are painting with car polyurethane using this process:

- we sand the MDF surface
- 3 coats of primer (cathalyzed) , 5 minutes at most between coats
- we let it dry and sand it before the paint coats (going higher in grade)
- 5 paint (cathalyzed) coats, 5 minutes at most between coats
- wet sand (1200) and polish

The result is good but not what we were aiming to. Basically what I mean is that objects reflected on the painted surface show no sharp edges. The other problem is that despite the fact that joins and screw caps are completely even before the paint proces, you can ALWAY see them after it is painted. You can hardly feel them, but you can surely see them when you look at the surface at 45°.

Could somebody give me a detailed explanation of what can we do to improve this result and obtain what we are expecting? Thanks

(english- ok, spanish - better)

[outback]

Hi York and welcome. Your English is fine, better than most of us here.


I reckon your'e trying to do the impossible, but I'll watch with interest and see what the experts say.
Have you considered a vinyl wrap of some sort?
And, what are you building?

Good luck.

[barryr]

how about a decent sanding sealer first ? I'm only guessing as I don't use MDF !

[echnidna]

You need to rub back so that you cannot feel any variation in the surface at all.
You could cheat and use a layer of spray putty after the first sealer coat.

[Harry72]

Theres no need to sand the face surface on mdf unless its been damaged(sanding with under 1200 grit damages it IMHO), the end grain(not that you can call it that)is what needs the sanding/sealing. If there is face surface damage do as echnidna said, seal then spray putty it.

Personaly I dont like using paint to seal mdf endgrain much prefer resin(epoxy or polyester), it holds the end grain fibres way better than paint(and only one coat), it can be polished to a very shiney finish before painting.
As for the screws showing through dont use them where they can be seen, mdf glues very well and doesnt need screws if the panel size is small, larger panels can have battons glued on the inside of corners for strenght.

I used to be a car audio nutter... but now Im a woodie!

[yorkincr]

Thank you all. This forum is great!

I want to state that Costa Rica is a small country and going to the hardware store is not as funny as it might be in yours. Maybe is possible for me to get here all the stuff that you are mentioning, but firts, I need to know how is it called here. I will appreciate if you can show me links where the products you mention are explained.

I really don´t know what vinyl wrap is. Right now we are bulding a small credenza. Finishes for MDF in Costa Rica use to be laquer...but we would like to innovate using this car polyurethane finish with mirror like shine...well, the same as in a car.

Sanding sealer, that sounds great. I am afraid maybe we don´t have something like that in the market because I explained my problem to som paint providers and they have only recomended putty. We have used putty over the screw caps and before paint it is completely even, but after paint you can easily look where they are (looking at 45° angle).

Epoxy (resin or polyester), this sound that something I would like to try. Is it possible you can explain me more or give me a link where I can learn more about this? Thanks.

I have seen this mdf finish on the internet, in furniture magazine, italian furniture, but not here in Costa Rica. I would like to be as close as I can to that finish that is called "piano finish" (or something like that), because you see that on those black pianos that shines like a mirror.


Muchas gracias!

[Harry72]

Try haunting some car/home audio forums for info on finishing mdf.

[Trav]

hola york!

I can't help with your question, but I thought I'd say that I spent a few weeks in Costa Rica a few years ago and loved it. You have a beautiful country! Lots of mosquitos though!

Good luck finding an answer to your questions.

Trav

[joez]

yorkincr,

Do you have access to Shellac? If so you can add talc (talcum power) to it to make your own sanding sealer.

Not sure how well it sprays on, but it sands really well.

Joe

[soundman]

What you are trying to do is achievable. Many cheap nasty pianos are made of MDF these days & they achieve a good result.

most important you must pay attention to keeping the surface quality as good as posible right from when you take the cover sheet off the pack.

handle it carefully.
avoid putting fasteners thru the showing faces of the material. MDF glues very well (as mentioned before) especially if you rebate your joints.
Bring your fasteners from the inside or use other means if possible.
Make all your machining as clean as possible.
From your PM I gather you have read my earlier post/s.
When beginning to finish, carfully sand the edges with 240 gritt paper to remove as much of the fuzz as you can it this stage (you wont get a smooth finish)

speak to an automotive paint supplier & get some high build automotive undercoat/ primer compatible with your top coat. (I gather you are doing opaque colours)

Prime your edges.
do your first run round the edges with a brush, being carefull to leave minimal build up on the faces, run round once more even while the last coat is still soaking in. Be generous but don't let it get sloppy or gluggy. you want it to soak in almost completely. Thinning may be helpfull depending how thick the product is.
let it dry well
resand the edges.
recoat the edges again dry & resand.
repeat till the edges are solid & smooth & all porosity is gone.

side issue of holes.
Any holes from fasteners or "problems". Make sure all screws and fasteners are sunk well below the surface, at least a mm or two. Always pilot and countersing screws before screwing, A pilot & counter bore drill is a good thing. Sand off any hairy edges & scrape off any deformed bur from screw insertion. Fill all holes with automotive filler.
Do not be over generous with the filler, any excess will have to be sanded off. Be neat.
sand back with 250 gritt till flush & flat with hard flat sanding block.
Spot prime the screw hole filler with the primer with a small brush & let it dry well & sand flush with 250 gritt. Be very fussy here re prime & re sand till prefect.
Carefully sand the entire surfaces with 250 gritt. Be particular about being smooth and flat and evenly sanded.
spray a smooth even coat of primer over the whole job (Not too thick or too wett) . Observe the behavior of the paint as it dries. Does it dry evenly or is it patchy, do some areas absorb more than others.
Carefully resand at 250 gritt & recoat with primer till the surface accepts the primer very evenly and shows no blemish both in the sanded surface & as the primer is applied.
Sand carefully and well to 400 gritt ( and beyond depending on the top coat)thru the grits.
Start your top coats as normal.
It sounds fiddly but you can get a process going. You will find how far you can push the process as you learn.
It is important to solve any problem as early as possible in the process.
If the screw holes are showing thru the primer they will stand out badly in your final finish.
be observant at all stages.

cheers hope to hear how you went.




fr

[yorkincr]

Thank you Soundman and all of you guys. You gave me a lot of homework to do (Shellac + talc, great receip, I will try). Right now, with all your answers, I have a great starting point for trying to achieve the goal that we are aiming to. I won´t be able to try this so fast, but as soon as I can I will let you know how it went, and if it is possible I will post a picture for letting you know the result.

[ian]

Only thing I can think to add to Soundman's great answer is to ask how fine is your polish?
I've seen "grits" as fine as 11,000 advertised for this sort of application

[soundman]

Fine abrasive will only effect the final gloss level.
York's problems are at the basic surface preparation level.
If you have surface imperfections in the substrate or finish coats after they will show in subsiquent coats unless sanded completely out. Using fine abrasive will just give the imperfection a nice sheen.
cheers

[Tools]

Nordsco Easy Sand'n'Fill is the go.It is an acrylic and is brushed on,and you can get a mirror finish from it.I have done it and then added penetrol to the enamel and brushed it on.

Tools

[Toymaker Len]

Thats brilliant Soundman and covers it all about 110% but I have to ask our friend York in Costa Rica is it not possible that they may have some beautiful native timbers which will make his credenza even better ? (Sustainably harvested of course).