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When doing a primer coat do I need to get everything or can I pretty much fly through it leaving it kinda blochy?

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I find that primer dries so fast that you have to do the job quickly, but it's worth it in the long run to get it somewhat even: any time saved by doing a poor job of priming will be more than made up for trying to get the finish coats looking good.

The primer coat doesn't have to be perfect, but it should cover the surface (no bare spots) and it shouldn't be so blotchy that you get drips or visible unevenness.

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I find this to be true with every step of the wall finishing process. Easier to frame square than cover it with drywall; easier to get the drywall seams tight than fix with mud; easier to get the mud smooth than fix with primer; easier to prime than fix with paint. It just often seems better to fix it later because you feel like you're making progress that way. –  Steve Jackson Nov 13 '10 at 20:04
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You need to prime the surface thoroughly. The purpose of the primer is so give the surface uniform absorbtion properties. I'll need an extreme example to illustrate that.

Recently I tried to paint the wall already covered with glue liming - the cheapest water-dispersion paint possible. The old paint had good adhesion to the wall and looked solid, but when I started to paint I just couldn't shade the new paint - when the new paint contacted the old one the latter absorbed all the water immediately and the new paint got dry before I could do anything.

This is how I found that priming is a good thing. However that was not all. I discovered than when the first layer of primer is applied it looks uniform at first. However when it dries up and I apply the second layer I see dark spots - those are areas where I underapplied the primer during the fist pass and now those areas still absorb water and thus become dark. The third layer of primer doesn't leave dark spots anymore - all the surface is thoroughly primed and the new paint applies allright.

Once I tried to paint over the first layer of primer - it turned out well except those underprimed spots where paint would still dry up very quickly and wouldn't be shaded well.

The bottom line is: prime with at least two layers until the primer doesn't leave dark spots on the surface.

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+1 Great example and exactly what I'm running into. You convinced me to put on another coat of primer and hopefully will have saved me from wasting money on the much-more-expensive paint. –  JML Nov 9 '11 at 13:04
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It will come out blotchy because many times it is very thin paint. Spread it on with no drips and let it dry well. You may want to apply multiple coats as needed. It typically will dry fast so you may be able to perform additional coats within an hour after first application.

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