# Spray Paint didn't stick



## ChunkyC (Jun 28, 2009)

I use "shop projects" to work on different finishing techniques and finish combinations. One of the techniques that I tried this weekend was painting MDF. I've read a couple articles about sealing the edges of MDF with joint compound and then sanding smooth once the joint compound dries. Then you prime with an oil based primer and paint.

This was the result:









2 coats of Primer and 2 coats of Red Rustoleum.

I will admit that the red Rustoleum was not "fresh" and it's normally stored in the garage that gets VERY cold. I would be surprised if it hasn't been frozen at least once in the past. Ergo, this could be just bad paint, I don't know.

My house is cold, about 61-62 degrees (I'm a big guy and I like the cool) so I warmed the can up by placing it on the register for a few hours before painting. The paint was 70 degrees when I applied it.

Any thoughts to why the paint didn't stick to the edges completely? It almost looks to me like something contaminated the primer after I applied it.

Thanks,


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## bigike (May 25, 2009)

did u try to go over it again?


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## wseand (Jan 27, 2010)

Not sure what could have contaminated your primer, to do that. Maybe it didn't cure properly. I would invest in a heat lamp to help cure your paint between coats. But I have never used MDF or spray painted wood so not sure how it reacts to paint or joint compound. Maybe it was your compound that it wouldn't adhere to. I would start the experiment over with fresh paint and more heat.


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## wseand (Jan 27, 2010)

Maybe the Painter Touch and the Stops Rust are not a compatible combination. I looked on their web site a bit and didn't see anything but you might want to try using the same types together.


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## ChunkyC (Jun 28, 2009)

In the house / Shop is where I painted it and left it to dry. I have 3 other "samples" that I did roughly at the same time:
1 - MDF w/ 2 coats of GF Sanding Sealer and 1 coat of Gloss Poly applied with a foam brush
2 - MDF w/ 1 coats of GF Sanding Sealer and 1 coat of Gloss Poly applied with a bristle brush
3 - BB Ply with 2 coats of spray Satin Poly.
4- MDF w/ joint compound on the edges for sealing, 2 coats of primer, 2 coats of paint.

No.s 1 though 3l three came out fine. The painted MDF is the only "sample" that I had troubles w/.

So far #1 is the best finish of all 4 "samples" and the one that I use all of the time but I usually w/ Satin verse the Gloss Poly.


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## ChunkyC (Jun 28, 2009)

Bill: I would think that if the two aren't compatible that I would see the paint failing in other areas. Do you think this is not the case?


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## wseand (Jan 27, 2010)

Truthfully, I am not sure. I would venture to guess that they are different compounds and may not be 100% compatible. Each type says to use that specific primer for it, but as I have been learned that this is not always the case. In your case it does look more like it just didn't cure properly or like you said it got contaminated from something. 
MDF is cheep so I would just try it again and see if you get the same results. Like I have said I don't use MDF but I would go with three coats of primer on it and two coats of the paint. From what I am told it soaks up a lot of paint. And spray paint doesn't usually put on as much paint as a brush would.


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## ChunkyC (Jun 28, 2009)

Thanks Bill. This is why I use "shop projects" to find what works and what doesn't. This certainly didn't work for what ever reason.


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## stevenhsieh (Jan 8, 2010)

Which Rustoleum primer did you use?

The VERY BEST, most practical is: sand the heck out it.
OR shellac would work.


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## ChunkyC (Jun 28, 2009)

Painter's Touch


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## stevenhsieh (Jan 8, 2010)

That brand product is horrible to use.


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## stevenhsieh (Jan 8, 2010)

IT would not make a differemce if you use a foam brush or bristle.

On your 
*4- MDF w/ joint compound on the edges for sealing, 2 coats of primer, 2 coats of paint.*

Prime the MDF first, 
then joint compund,
sand, 
remove and dust, 
prime
then paint.


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## ChunkyC (Jun 28, 2009)

"IT would not make a differemce if you use a foam brush or bristle."

I get a better finish with a foam brush almost every time. I know that you should use a natural bristle on oil based finishes but I always seem to get a load of bubbles in the finish. Maybe if I would purchase a high $$ natural bristle brush I'd get better results but I get good results with the 2$ foamy.

I'll give the prime, seal, prime and paint technique a try. I'm going to have to sand down what I have now because it can't stay like this. Every article that I've read to date was seal, prime then paint.

Painter's Touch was what was available at the local hardware store in oil based primers in a spray. Do you have a better option that I might be able to find?

Thanks for everyone's help.


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## stevenhsieh (Jan 8, 2010)

*Zinsser High Hide Cover Stain Oil Base Primer Sealer*


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## Earlextech (Jan 13, 2011)

The edges of mdf must be sealed before any coating, including primer. Gluesize is the way to seal it properly. One part glue to one part water, brush on with a chip brush. Let it dry, then sand. Repeat this until the edge is smooth. It's pretty easy to see.


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