Need hellp using MDF

I have used MDF again to achieve a complicated layered octagon picture frame. We made a unique MDF build up about 6 months ago on a different project.
Raw MDF sucks up material and needs sealing. I wanted a super smooth, high gloss paint finish that would look a bit like molded plastic.
Frame one - about 2' x 4': Wood working went quite well. Thought I grabbed the shellac based sealer, but had the water based urethane. Proceeded with several coats. Sanded to 220. Painted with Rustoleum high gloss black spray cans. This paint says to recoat within 1 hour or wait 24. After 24 hrs had a beautiful finish, but decided to give it a light rub out and one more coat. Disaster - crinkled all the coats extensively all over the frame. Sanded completely and reperformed with outstanding success.
Frame two - 54" diameter octagon: Made sure I had the shellac this time. Careful job of sanding all edges, etc to 220.Multiple coats with sanding between coats again to 220. Nice finish on full length pieces, then cut the octagon sections, cut spline slots and biscuit work, glue and assemble. Sand any and all imperfections with 3M superfine sanding pads. Man this things looks good. Spray mist coat with Rustoleum High Gloss spray can(s) and continued mist coating on a 30 minute rotation until good color and finish on all surfaces ending with a "full wet coat". Looked really good, but that high gloss sure points out minute imperfections. Honest 24 hours. My partner decided to give it one more light sanding - nice look and feel, but without gloss. I wasn't there, but he shot one more coat and we have a crinkled mess again. We will get this, but it sure is frustrating.
Any help?
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I suspect that if your initial coats are fine and your subsequent coats are having problems I suspect that MDF is not your problem. More than likely your surface is becoming contaminated between coats. And yes as with any high gloss application imperfections do show up like a sore thumb even on glass.
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DanG wrote:

Wait longer. *MUCH* longer. That or do all at once and forget that last coat or forget rattle cans.
I've had exactly the same experience with rattle cans regardless of the manufacturer. Pretty much regardless of whatever they are spraying too except - I could be wrong - for flat paints.
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There are so many elements to this. I suspect the humidity was higher than needed - thus needing a longer dry time. Often shops are not heated at night - and the humidity rises high at night and drops during the day. If in a controlled atmosphere you would have better luck.
Martin
dadiOH wrote:

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DanG wrote:

I had a similar problem with Rustoleum crinkling. In my case it was because I didn't follow the instructions on the can. IIRC, you can recoat withing something like the first 1/2 hour. After that you have to wait several days or the previous coat will bubble up.
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Here in the UK we have an MDF-alternative called Valchromat. It was widely used in the '80s for that Italian post-modernist furniture. It's basically MDF, but with more resin than usual and with a coloured dye. I use it in "slate grey" to make fake stonework frames that are taken straight off the router and wax polished. If you're shellacing it afterwards, it also builds very quickly to a film finish. I even use it for woodturning - stack sewn rings into a small-mouth oval bottle, turn and then lacquer (shellac or urushiol).
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used lots of it from the rattle cans myself. Standard rule I soon adopted was to wait a minimum of two days between coats. I knew people who waited even longer.
I have projects in metal that have been outside for over twenty years without any rust.
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On Sat, 10 Apr 2010 14:22:52 -0400, "Lee Michaels"

The 24 hour number is under optimal conditions with only one light coat drying. You may have to wait as much as a week or more before recoating (sand lightly or it won't stick). The trick is that *all* the solvent from the previous coats has to have evaporated so the cross-linking can complete. After that you are good to go. I have had trouble even after a week if it is a bit cold or if I put down several coats initially.
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Tim Douglass
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I agree. I make some stuff from MDF once in a while. I came to the conclusion that the first coat of finish paint is sacrificial. Paint it, wait a week, sand it smooth, then give it a finsh coat and it will turn out great. Greg
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wrote:

In this case the problem is not the MDF, but the paint. I've tried sealing MDF with shellac with fair to middlin' results.
-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"
Tim Douglass
http://www.DouglassClan.com
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I used some last year on two laptop tables. Took me a few weeks with the humidity and dust to get them right and I still wasn't completely happy with the last one. Had the most trouble with the clear coat showing dust. After a couple of weeks and 4-6 very light clear coats, they finally looked good and have been holding up to daily use well.
`Casper
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