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:
- I preferred a foam roller for applying waterborne primers - i used Axus decor hd foam. It resulted in less stipple.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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:)