Sealing MDF for paint? + Gluing/painting rubber

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Michael Bergeron

Legendary Member
RPF PREMIUM MEMBER
Thought I'd throw this out there because my research has returned mixed results.

How do you seal MDF so that it paints smooth? MDF absorbs LOTS of paint...

This is for my HIC. I want it to have a smooth surface like metal both on it's face and the edges. What do you normally do to get this kind of result?

Also, while on the topic of HIC. I've got one of Stormrider's awesome rubber casts. What do you use to glue/paint the rubber?

Any advice much appreciated!
 
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Finhead

Sr Member
Re: Sealing MDF for paint?

I would use a vvarnish to seal the MDF.
What kind of rubber? Urethane I'm guessing, I would use either ure-bond or superglue gell to glue it down. Painting is a little more involved and really depends on the type of rubber.
 

Pete SSS

Well-Known Member
RPF PREMIUM MEMBER
Re: Sealing MDF for paint?

We (in the UK) have a product called Sanding Sealer that's used to seal MDF prior to painting. It's just a specific varnish, designed to deal with MDF's serious drink problem.
 

Stormy320

Sr Member
RPF PREMIUM MEMBER
Re: Sealing MDF for paint?

The edges seem to be the hard part. Not smooth and very porous.
 

Michael Bergeron

Legendary Member
RPF PREMIUM MEMBER
Re: Sealing MDF for paint?

The HIC I bought was from this thread:

http://www.therpf.com/f13/closed-see-new-list-hic-han-carbonite-88442/

Looking at it again he says:

I use only high quality alumilite rubber. It does not (That I have EVER seen) dry rot or crack. it takes laquer based paints well
So what's a good lacquer base spray out there that might be the colour I need?

Thanks for the tips on the MDF. For the edges I've heard that drywall compound works well to fill the gaps. Then I suppose I would sand and varnish over that before painting. Sound about right?
 

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Finhead

Sr Member
Than it is Urethane. I would start by washing your pieces really well with dish soap and water this will take off any residue that the rubber has leached and or silicone/release agent. For painting urethane I use acetone to give it some "tooth" then spray your paint which I also cut/thin with acetone. Ligther coats stick better and wont flake. Any lacquar based pait should work, dulicolor or the like will be your easiest to find unless you have access to automotive grade paint. Here's a thread on the BOTB if you want to read through a few different tech on how to paint urethane.
Forum ~ Runboard
 

Michael Bergeron

Legendary Member
RPF PREMIUM MEMBER
Thanks! I tried my primer on a small piece that I cut off and not only did it stick well it doesn't peel/flake at all when I twist and stretch the rubber (I gave it more abuse than Han will ever actually get). I think we have a winner. :)

I'm definitely using duplicolor paints. I've fallen in love with them since my ST3 phaser & Vader helmet. :thumbsup
 

James Kenobi 1138

Master Member
RPF PREMIUM MEMBER
Recently I used spot putty on MDF for a smooth finish.

I sanded as smooth as I could get it first. Then I used a clear polyurethane to seal the wood. Primer next with a light sanding. Then I squeezed out the spot putty like toothpaste and used a smoothing tool to spread it in a thin layer. A repeated this all over the surface until it was covered in a layer about as thick as a piece of paper.

After it dried fully I sanded it using a large flat drywall hand sander (the kind you use to sand drywall joints flat and smooth). After sanding the spot putty was about 1/10 the thickness of a piece of paper and smooth as glass.

Then another few coats of primer to 'lock' the putty down and give it strength, then I painted after everything was dry.
 

Michael Bergeron

Legendary Member
RPF PREMIUM MEMBER
Another great idea. :)

I'll try the varnish first and then try the spot putty if it's not smooth enough for me.
 

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BornKilr

Sr Member
RPF PREMIUM MEMBER
I've never personally tried it, but a guy that used to work with me making signs & building displays used to seal the edges with thinned down joint compound. They always looked really clean.
 

Noeland

Sr Member
I had no idea you had to seal MDF. I've only worked with it a few times though, and never had to paint it.
 

Michael Bergeron

Legendary Member
RPF PREMIUM MEMBER
I had no idea you had to seal MDF. I've only worked with it a few times though, and never had to paint it.
If you don't mind using a boat load of paint you don't HAVE to. Makes life a lot easier though. :)

MDF absorbs a huge amount of moisture so painting it the wrong way results in a rough texture and about 10 coats.
 

exoray

Master Member
I use Shellac and steel wool. It has been the best solution I have found to date.
Shellac is my preferred method, and has been for many years, it just works... You can get multiple recoats done and sanded in just a few hours... You can use a small nap roller for flat surfaces vs brushing to save time... Clean up with common household ammonia, followed by a soap and water bath so you can re-use the brushes and roller later...

Brush on clear lacquer also works well, as a sealer but it's not as universal in regards to top coat compatibility, shellac that can be top coated with just about anything, some top coats will mess with a lacquer undercoat...
 

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Pro Mod

Well-Known Member
RPF PREMIUM MEMBER
In the UK we can buy different types of MDF primer.
The one we use most of the time can only be sprayed, but we also use one that can be applied by brush or roller.
I would think these types of product would be available near you.

When time is critical we sometimes cover the cut face (small areas) of MDF with thick super glue and sprayer activator on it. Works every time!
 

elro

Active Member
I use spray putty or primer filler once the main shaping has been done (along with blade putty).

The blade putty goes down on any area that ive cut through the mdf (the most likely porous regions). I let it set, then sand, then apply more if neccessary.

Once im happy with it I give the entire thing a coat with spray putty / primer filler and sand it to 1200. this has always worked AOK for sealing mdf off.

Another advantage is that you can be quite messy doing these steps as you are still able to to all your nice sanding work before layering down your clean layers of paint (by 'clean' i mean finishing).


In terms of gluing ANYTHING to MDF, ive gotten away with (in different applications)

Plastic to MDF - scraped notches into the MDF, mixed some epoxy putty, and smooshed them together ( google : NOWKISS.JPG )...

Styrene to MDF - Bargain store cheap instant glue works really well - It helps that the MDF absorbs liquids easily as it bonds onto the styrene and then embeds itself into the MDF.

Cast resin / resins etc to MDF - Just Bargain store 2 part epoxy glue - It manages to stick down very well and doesnt let go.

^ All methods above give me a really good grip due to the nature of MDF absorbing the glues. Really most would would AOK.

In specific terms of rubber though I personally would use the instant glue stuff (For smaller pieces), if it is a larger piece most likely the epoxy glue (Epoxy glue is a bit messier to mix and less accurate most times than instant glue, depends how you work really?)


Hope it all works out AOK for you!
 

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