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Finishing MDF

Hi TP community -

I would very much appreciate some advice/comments on how I can improve my finish on painted MDF using a water based approach. My goal is to achieve as close to a brush-less finish I can achieve with my limited experience and available time…

The materials, tools and process I have adopted (learnt from this community:grinning:) are:

Materials and tools
New unfinished Medite 18mm thick MDF panels
Mirka Abranet abrasives on Bosch GEX 125-150 random orbital sander and a Mirka block
Teknos Futura Aqua 3 Primer
Teknos Futura Aqua 20% sheen top coats
Two fussy blokes 5mm nap microfiber rollers sleeves, 100mm
Royal Langnickel golden taklon brushes for laying off

Process (along with corresponding image)
Primer coat with roller
Quite a heavy sand at 180p to flatten primer – not completely flat
Primer coat with roller
Sand quite heavy with 180-240p to flatten primer – not completely flat
Top coat applied with roller and lay-off with 75mm wide Royal Langnickel
Sand with 400p to flatten
Top coat applied with roller and lay-off with 75mm wide Royal Langnickel
Room temperature low 20’s with still air
Dust was removed after each sanding stage with a vacuum, microfiber cloth and finally a tack cloth
Drying time between all coats at least 12hrs majority 24hrs

Linked is a photo of the final finish. The photo was taken under direct light to expose the flaws - in flat / indirect light the brush marks are not visible.

Thanks in advance for your time and responding to my post.

Cheers
Angus

That’s pretty thorough!

Are you getting those brush marks with every coat? Check out the following to see if they make difference.

Could be the laying off brush is putting paint on, rather than levelling out what is there. ie Make sure your brush is clean not clogged.

You could be laying off when the paint is going off ie not being quite quick enough with laying off.

Maybe the paint is applied too thin, so try applying it a bit thicker to see if it flows out better.

Is the primer coat providing a non absorbent base for the topcoats to flow out well? As an experiment, try applying the topcoats over a glossy primer or old gloss paint. You may see better flow out of the topcoat. Also see how the sheen compares to your finish on the MDF. If it is considerably more shiny, the MDF primer you are using may need to toughen up!

Homework :slight_smile:

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Thanks for responding Andy. Homework welcomed:)

You’ve made me realise that I have some Tikkurila Otex for another job (not started and totally the wrong colour for the current job). I’m thinking two coats of this would satisfy your suggestion to apply the top coat on a more robust/glossy substrate?

I’m have my suspicions that the sanding needed to flatten the primer and the primer itself is resulting in a porous surface. It not a particularly high-build primer, so I may try three coats.

Brush marks improve with each top coat.

I’ll also look at the various techniques you’ve suggested.

I’ll post back once I’ve made some progress.

Thanks again!

Angus

I thought I’d share a little about my experience attempting to achieve a brushless finish on MDF with water based paints. I got very close but ran out of time on this project.

Here’s what I learnt:

To achieve a brushless finish takes skill, a technical understanding how each material behaves under different conditions, how different materials might react, and the right tools for the different stages in the process.

Not all MDF is created equal. I suggest using Medite or equivalent finishing grade material. In my experience the fibres in cheaper materials may swell with water based products and slightly with solvent, ruining any chance of a smooth finish.

Priming. Im my experience, provided you have the skill at applying the top coats, the finish you achieve at priming stage sets the baseline for the final finish. The primer coats must be smooth because the top coats have very little filling capability - imperfections in the prep/base coats will show through.

In my experience Dulux MDF primer does a good job at sealing mdf but causes the mdf fibres to swell which ruins any chance of a smooth finish.

Teknos future aqua is OK but doesn’t entirely seal the surface. Even after two coats that cover the surface the dry time for the top coat is too quick affecting flow out. Thinning 5-10% helps, but only so far because water causes mdf fibres to swell.

Zinsser BIN. MDF is sealed after two coats. Paint flows out well and nearly no brush marks.

Tikkurila Otex. The best I have tried. I suggest two coats. MDF is sealed and sanded to a mirror flat finish.

Abranet going through the grades up to 400p on electric and handheld sanders with extraction are essential. As is avoiding clogging and anything that might scratch the surface. As a reminder, water based paints are poor at filling imperfections.

Top coats. I found equivalent levelling properties with Teknos and Tikkurila waterborne paints.

Tools and equipment:

  1. I preferred a foam roller for applying waterborne primers - i used Axus decor hd foam. It resulted in less stipple.
  2. I preferred a soft synthetic bristle brush for laying off WB primers - the best I used was Wooster Pro Soft. I found less dragging with a soft filament.
  3. I preferred a microfibre roller for top coats - I used two fussy blokes. They carry loads of paint, spread evenly and the paint levels well.
  4. Firm brushes for laying off - I used Wooster Pro firm, Purdy Sprig and Royal Langnickle. All did a good job, with the RL being least favourite. In my experience the viscosity of top coats require a firmer bristle to assist levelling.
  5. I used Axus trays with liners. This allows one tray but multiple liners with different paint. Great when you’re experimenting with thinning the same paint at different rates.
  6. I used a mixture of roller cages. I found least compatibility with the Purdy cage especially with foam rollers. It critical the rollers glide effortlessly to spread paint evenly and to avoid any roller drag.
  7. Allowing each coat to dry thoroughly is also key. I found best results with 8hrs plus, but sometimes one just doesn’t have the time and the job needs to get done.

If I were to start again and higher VOC not be an issue I’d use Otex as the base followed by waterborne top coats. Another thought would be to try and find a specific water based sealer followed by primer and top coats. Another consideration is to use Medite moisture resistant MDF.

I hope this helps some folks on the forum:)

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Thanks for a really comprehensive post, very helpful to future readers.

Have you looked at Tikkurila Akva primer, (water based Otex) that would address VOC concerns.

I’ll checkout that primer on my next job:)