Ok my LR3 (and my primo) has a full MDF top. Larger than just the spoilboard area. I live in Florida where the humidity is almost always 90%+ and I also have kids that like to come out and see what I’m working on and set whatever drink cup they have on the closest flat surface where it can sweat and leave water rings. What is the best thing to use to coat the MDF to give it some sort of water protection? Hoping for something easy to apply that I don’t have to take the LR3 down for. Open to any suggestions. Thanks!
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Shellac or water-based polyurethane would both work. Both can be brushed on. Water-based poly is easy to use and easy to clean up.
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Boiled linseed oil does the trick for me. Penetrates so it lasts quite a while.
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I used acrylic. So far so good. 
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My favorite thing about shellac is it dries in like 10 mins. It is made from bugs. Which is kind of gross, but probably better for you than dust from polyurethane. It doesn’t really matter though, because mdf dust is worse.
BLO is easy to apply, but I haven’t found it that water proof. I haven’t used it on mdf though.
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My main desk at home is polyurethane on mdf and I set wet drinks on it all the time and it is fine. I think it was 3 coats, sanding in between.
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Eh, the old records are made from it as well. A silk scarf are also boiled caterpillars. Glue used to be molten horse… 
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A little Stumpy Nubs told me shellac wasn’t alcohol proof.
Could be a problem if the kids are old enough…
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You and everyone here probably have eaten it, maybe even today. It’s used to make candy coatings shiny. 
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I’ve found water resistant mdf that I’m using on mine. Also in Florida. So far there have been no issues even after surfacing
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I had a twix. But no bugs today.
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That’s what they want you to think. Dundunduuuun.
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“Natural flavors”
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I live in a similar climate to Florida.
Shellac is great as a seal coat, but it’s not waterproof, which is why your Mum used to go mad when you put your glass on her French Polished table. I have used shellac for sealing MDF jigs, but I often give them a coat of paste wax as well.
I just use a couple of thin coats of waterbased poly - watch the ends though and don’t thin the paint. I use flat if I’m just going to seal it and gloss as a finish (gloss waterbased is really like a high sheen satin anyway).
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Used to work in an industrial bakery… still have a hard time eating bread… just can’t unsee the seen… three most terrifying words are, “food grade grease”. 
Thanks for all the replies. Sounds like water based polyurethane will be the easiest to deal with so I will give that a shot.
Doesn’t MDF swell up when "painting "?
I would say; just buy green (waterproof) MDF and save the hassle of waterproofing it!
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Came here for the ideas too.
Thought I might add a little tid bit for the natural flavour ppl.
Beecareful you may burn your house down.
This is true IF you do not properly handle the cloth that is coming in contact with the BLO. Most of that spontaneous combustion happens when ppl use rags or staining cheesecloth, etc. to apply/wipe off the excess BLO and then just throw the rag into a waste bin and leave it. the chemical breakdown process of the BLO causes high heat as the cloth is “folded” over on itself and has no where to dissipate to. The best practice I have used is to lay the rags out flat on a surface and allow them to dry just like you would do your project/wood. This allows the dissipation of that heat (really it has no place to build up) and not have the “spontaneous” combustion that you often read about.
Just my $0.02, but I have done it whenever I have used BLO and have never had a fire. As with anything, proper adhearance to guidance can save a lot!!
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