We are trying to make the conversion to waterborne pigmented. We've been using Sayerlack clear for awhile now and have it pretty well figured out. It's a great product. Now we are trying the pigmented version with one of the "universal" water primers underneath - SW Gen 2 primer.
The problem is that the "grain" of the MDF keeps getting raised with every coat. The MDF is Ranger, so good quality. We've been told not to hit the MDF with lower than 320 and to think of it more like polishing instead of sanding. That helps, but it's not perfect. Also, if you have any joint or defect on the MDF, you can't avoid sanding it a bit. We keep coating it, but as soon as we sand the fir off, we've opened it up again and the next coat does the same thing. Maybe we just need to expect it not to look as good as CV? It looks great on maple!
Anyone have any ideas or tips we can try?

We apply one good coat of a transparent WB sealer over 220 grit sanded MDF
After dry, sand 400 grit
And then the WB colors, 2 or 3 coats depend on color, always sanding 400 between coats
It is the best result we get

We use Ilva 1k primer on Mdf daily, seals it up just fine. On machined (raised panels) we prime without any sanding, then sand and re prime. It seems to work for us.

I feel your pain. Chasing the grain. Years ago I switched to Zinnser Bin shellac primer. 1st coat hit with 320 by hand, 2nd coat w/400 and it's perfect. Then GF white undercoat mixed roughly 70-30 with leftover topcoat and then 2 topcoats of poly white tinted. No more telegraphing. More work but it's perfectly flat.

Mdf or Hdf either 2 k poly primer or a quality Vinyl selaer is a must.
Primer coat is more important than the color coat when you are working with mdf or hdf.
It basically seals the substrate and blocks the humid or anything that will affect the color coat.
There are many ways to finish the man made wood.If you are shooting for a constructor grade finish just spray the 2k poly primer(renner,ilva,gemini,centurion) what ever you work with.Has to be 2k for minimal grain raise.sand down with 320 and spray your color coat.
If you are running for a pro grade high end finish there are some steps you need to follow:
Guide coat and sand down to 150 for a flat surface
Primer coat either vinyl sealer or 2k poly to face and edge.sand down with 320 until you have a flat primed surface with out orange peel.
spray your choice of color coat.
I never skip the guide coat when i am working with man made woods.there are machine marks and they need to be sanded down before primer.
Good luck.

Hdf surface . 2k primer and 2k color coat

View larger image

I’ve had good luck with Gemini Evo white eclipse primer. I don’t pre sand raw edges unless to remove saw marks. Usually 2 coats.

Thanks Everyone. We are still struggling with it.

Bart, I think our next step is to try BIN primer since it is alcohol based instead of water. I realize that's not going completely waterborne, but denatured alcohol is not so bad. Your process is 3 different materials and 5 coats. Hopefully we don't have to go that far.

Yakuz, you seem to be talking about all solvent based products. We've had zero problems using CV primer and topcoats getting a flawless finish for years now. We want to move toward waterbased.

I caulk all my paneled doors/drawers after sanding the 1st coat of Bin. This causes a bit of grain raise. So before 2nd coat of Bin I sand/scuff the perimeter w/320. It's super quick sand, blow and go. The 3rd coat is a barrier to make sure the topcoats adhere. The MDF panel quality varies a lot. If you don't caulk and use good quality/higher density MDF you could/might get by with 1 coat of Bin. But I'm picky.

BTW I only put 3 coats on the backs. 1 coat of Bin,1undercoat and 1 topcoat. It telegraphs for sure.

I can get a batch of doors(25-45 pieces usually) in 4/5 days. I used to do the same process w/all WB sometimes adding 6th topcoat/day chasing the grain. :(

And I haven't any adherence issues in 5yrs+.

cheers
Bart

I've actually found a handful of old posts on here about Ranger MDF, despite it being considered "premium" being a bit of a nightmare with waterbase finish. Think we'll try some Weyerhauser 1st.

I spray only Waterbornes, Axalta, and Gemini. I have found that even the top Ranger board board products don't get along with waterbornes. I find Trupan Superior Plus the best for Waterbornes

Ptup, its all water base what i am talking about :) if you dont know whats the 2 k finish probably you dont know what you are doing :))))
yeah keep searching.

Well Yavuz, I'm not sure I can claim to know what I'm doing but have been spraying or managing spraying for over 20 years now. I have actually used multiple different 2k Poly's, but only the solvent based ones such as Polarion and the Accessa versions.
I have yet to see a waterborne vinyl sealer though. Please enlighten me.

Some one should let Yavuz know their are 2K WB's. Chemistry? It's a .........

Pdub. It's just 2 products. Bin and General Finish.