When painting a room, can I use one thick coat of paint, or do I have to use two coats?
I would recommend against one thick coat. Paint dries and "cures" best in thin coats. Let me explain- when you're done painting a wall it dries to the touch in a few hours. However, if you were to push into it, you could probably still move the paint around on the wall for a few days to weeks after painting. That wait is the "cure" time. How long it takes for the product to reach full hardness. Generally if you read the back of the container, it will give you an idea of the cure time.
Two thin coats of paint will dry and cure much faster than one thick coat. It simply takes too long for air and circulation to reach through that thick coat. If the top of the coat dries faster then the undercoat, you can get cracking and a failure of the product.
Generally when you're doing a room, the walls are dry enough for the second coat right about the time you're done with the first.
I've read the answers below and as a painter for the past two decades the answer is this: You need two coats of paint.
Sure, you can slop the paint on the walls as thick as pudding but it's going to look like crap. And those who think you can get away with one coat of paint that claims it'll cover in one coat, don't hire them to paint your house. I'll walk in the door and know - instantly - which walls were painted like that.
Scottie Vosburgh has the most detailed answer and you should take their advice.
Just one note on cure time. It's not just the hardness of the paint - it's also the color. It takes time for the color to set properly as well. Now, you many not notice but I would.
So, do it the right way and though it may take longer, the finish will last longer.
You should go with two even coats rather than one very thick coat. One thick coat is likely to drip and possibly chip. Most important thing in a nice paint job is the prep work- clean walls, patching holes and sanding lightly, then wiping down any dust with a damp cloth before applying paint. Two coats will ensure even coverage and correct texture of walls, it will look better than one heavy, rushed coat.
Iv been a painter for 30 years The only time it's possible to paint with 1 coat is if the colour is exactly the same fill your walls twice as filler shrinks sand them spot the filler with one coat by brush cut in by brush roll with a 10mm pile heavily load your roller and roll your walls with long rolls top to bottom this is important no small little rolls in every direction you see in home improvement tv shows once you rolled a good 2–3 metres of wall roll over your wall with your semi empty roller we call this a dry roll it will spread your still wet section of wall with an even finish, if the colour is different even just slightly different you must apply 2 coats
If you are going over the same color and Sheen. One Coat of premium paint should be fine.. Sand and prep the wall properly.. Spot prime any repairs or anything that you think might come through one coat. Apply paint generously but not heavy. Use a 3/8 or 1/2 inch Roller cover... The stiple will be tighter with the shorter hair roller cover.. Rule of thumb is a full roller cover will roll out a 4 by 4 feet of wall.. Imagine a big square or one pass top to bottom on an 8 foot wall.... Let it dry properly.. If you don't like the way it looks.. Give it another coat!
There are paints where one coat coverage is adequate. If you have good coverage in one coat there is no reason to apply two coats.
Many newer paints (better technology) go on thicker and a second coat is not necessary unless you need to cover a heavily saturated color.
There are three national brands of paint we recommend and always suggest using the top lines within each brand, rather than their lower priced contractor grade paints.