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Frankg

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Reply with quote  #1 
I notice the MDF absorbs the spray primer quick. Do I need more than one coat???
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Ken Martin

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Reply with quote  #2 
Hi Frankg

First question is; what kind of paint are you using.  Acrylic craft paints, Spray primer, water based primer, oil based primers etc.

The simple standard answer is yes.  The factory finish side of the MDF will not absorb as much as the cut side of the MDF.  The cut side, where you have cut, will absorb much more primer and you get quite a bit of the rough pop outs.  The edge will need to be sanded to get it smooth again, then another coat of primer before you paint.

That being said, people have tried all kinds of things to seal the edges.
Wood glue and water mixed 1/2 & 1/2 then sanded works.
Lacquer works to seal the pores.
There are many things people have tried.
However, you almost always end up sanding and priming, and painting.

We learned from Larry Laing in Washington that he was using Acrylic metallic craft paints.  He said he uses two coats of paint only, sanding between the 1st and 2nd coats, the uses a brush on poly, and gets great results.  He sent me a couple of his toys so I could see the results in my hands, and he was right.  His finishes sparkle and look great.

We started experimenting with acrylic metallic and regular craft acrylic paints on wood and MDF and found we were getting great coverage with most colors.  Udie has done several articles about this subject and he is finding you don't need the primers as much as we thought.

We use a lot of acrylic craft paints, because they go on quick and easy, and dry fast, and when sanded out and finished with sealer, varnish, or poly look great.  Shinny and smooth.

One of the problems with most primers is that they are white, gray, or oxide color.  Well when you go to cover them with your acrylic craft paints you are trying to cover the color of the primer.
One example is when using blue craft paint, I could not get a good coverage over the white primer.  Four or 5 coats later I could still see the white.

Now when using the blue craft paint as the first coat, like it was the primer, then sanding then painting, I can get a great result with only two coats of paint.  This is working on both wood and MDF for me.

When using a spray paint like Krylon, it still needs a primer.  I use Krylon's white, gray, or oxide color depending on what the final color will be.  I also use Krylon's brush on gray primer when i have a difficult piece to cover.

A professional painter and cabinet maker told me the reason we are having success without primers is because usually the first coat of whatever you use will act as the primer.  Most people are taught, and believe primers should be used first because they are less expensive than paint.  However, in the crafts paints and primers there is not enough difference in price to worry about, I have found.

Frankg: I am the worst person at being patient when working on a project.  I have the attention span of a 4 month old puppy.  I used to go directly from the cut out process to sanding to painting.
Now I have to force myself to sand and paint some of the scrap from the cut before I start on the toy itself.  Especially if I am using a different wood, MDF, or primer and paint.
After a while you just know what works and what does not.

Also, there are a lot better painters and finishers out there on the forum and your info and hidden tips and tricks would be a big help.  Thanks ahead of time for sending in any info you might have on this subject.

I hope something in this mess will help, if even a little bit.



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Udie

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Reply with quote  #3 
Frankg

Priming MDF

Yes – it has been my experience that more than one coat of primer is required.

Cut surfaces of MDF do suck up the initial coat.

Don’t wait to find out your results on project pieces before you do a couple of spray tests.

 

Here’s a test to do – sand the cut edge of 3/4" MDF with 120 grit sand paper and give it a spray with your primer.

On another piece, sand the exposed edge using 220 or 320 grit sand paper and give it a spray.

You should see a difference in the amount of paint that is absorbed by the cut surface of the MDF.

Why – because using the finer sand paper closes the porous surface more, reducing the amount of absorption.

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