I disagree. I have sprayed and continue to spray water based finishesI'll try and give my tuppence. a compressor gun will struggle to spray water based unless it's really thin(these guns will spray thinners based stuff with the right tip)
It was me who mentioned 1,000 grit doctor Bob (because the OP said he was rubbing through to bare MDF). So I suggested either his coat/s were too thin, he was rubbing too hard/without a flat under-surface block, OR he should try going down to 1,000. That grit (3M W&D) has worked well for me.
We all have our likes and dislikes, and as I said in my own original reply, I'm NO expert AND I certainly don't run a production line!
Basically though, I feel that if the paint is properly thinned and filtered, there is little very little in the way of "real sanding" required to de-nib. Personally, I would never use a scraper as someone else mentioned above, but at the end of the day, I feel that whatever works for the individual is "right".
The OP should try all the suggestions above and find out what works for him - IMO.
When spraying doors I start at one end and immediately put on another coat and then another if needed, its much quicker thanI have problems with overspray on hvlp because using water based its to slow. OK on say a 4 or 5 inch newel. but murder on say a door. one statement hints that the paint is nearly dry because of the warm dry air. this tells you overspray from the last bit will make the first bit rough. ie its very slow putting a coat on.
You haven't been using silicon products near your board's by any chance
I’d consider this to be my area of expertise…
Water-bourn on mdf isn’t the best as it makes the fibres puff up. And really you need a primer first, this will fill the edges better and be easier to sand than coat on coat (top coat) that your trying to do, this is part of the reason it feels semi-cured.
The surface needs ventilation to go off, stacking will prolong/prevent proper drying…
I stack them staggered against a wall, like leaning dominoes, with space in between each.
10% thinners is a good ratio to aim for, depending on the paints viscosity more can be added if needed.
you want to have 30/40 psi of air at the gun, less will cause poor atomisation and too much will cause excessive overspray, dryness and waste paint to the air.
Ive got a £25 gun, works fine. Make sure to over lap by 50% and keep it consistently the same distance above the piece by you moving your whole body, not swinging the gun with your arm as you’ll get uneven coating
I used MRMDF as I'd heard that it is drastically different to MDF for water based products
That depends on your topcoat, if the topcoat gives a solid colour with 2 coats the it’s OK and good enough, if it doesn’t then you need a flat colour with the primer however many coats that takes. That is my approach and opinion.I'd also be interested in your thoughts on "how much" to prime. I've always figured that getting a coat of primer on is enough, it doesn't need to be completely opaque and "perfect".
That depends on the brand.
Medite MR is better than kronospan or caberboard.
Finsa hydofugo is reckoned to be better still.
The green all the way through stuff is not medite - that is brownish surfaces with green core
Spots sound like oil from compressor, your not sanding your polishing with 600s to get lumps out, scrape first light sand with p400, topcoat is too thin, warm it up first in a bucket of hot waterI've been stuck on the painting phase of my pantry build for a few weeks now and think it's time to ask some experts. For context, I'm currently spraying flat (no detail/moulding) MRMDF drawer fronts/doors.
Problems that I'm encountering
- After spraying I have occasionally found long streaks (as wide as a 5p piece, maybe 15cm in length) in the finish. I suspect this is oil finding its way in.
- After spraying I sometimes find what I can only describe as "scabs" in the finish. They're smallish (5p piece) bubbly raised areas. Only thing I can think is that it's oil again, but it's a very different result from the above.
- During spraying I struggle between getting enough paint on, and pooling/dripping. I suspect that this is a combination of (over?) thinning the paint, and inexperience.
- After spraying I de-nib with 600 grit. When I focus on problem areas (see pooling/dripping above) I invariably end up overdoing it and taking surrounding areas back to wood (MRMDF). Obviously "be more careful" is a solution, but does anybody have any techniques to help with this?
- After drying, the paint stays (very) slightly tacky. I can leave a fingerprint on it, which will go away within seconds. If I leave a painted item on something, the paint may stick to it and tear off when moved. Leaving two painted things touching each other will bond them fairly tightly, and will definitely result in paint being torn off. This situation doesn't appear to get much better with time. I have some items that have been drying for a week or more, that still have this issue.
Appreciate any advise that you can give .
- I'm spraying water based acrylic gloss that I thin with water.
- I'm using a compressor and cheap amazon spray gun. Compressor has a pressure regulator which combined with a little twiddly knob on the gun lets me tweak the pressure adequately (I think). I don't have any concerns with the gun, it seems up to the job.
- I have an inline water filter/trap on the gun. This is looking a bit worse for wear, may need replacing.
- I'm spraying outdoors. Bugs are a pita, but not much I can do about that other than move stuff indoors for drying.
- For drying large batches I stack pieces together with craft paper to keep the painted surfaces from touching. Could this be inhibiting further drying/curing?
Thanks for that - I shall have another look at Kronospan, it's possible I got that wrong.Its funny but I kind of have the opposite view, I like the Kronospan best as it seems denser and more resin heavy. I have found it makes a better edge and seems to take a moulding for handle recesses and stuff better. I found the Medite to be "fluffier" in general.
Not heard of the Finsa stuff you mention but might try it out.
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