Author Topic: sanding between primer coat  (Read 2254 times)

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Offline HAXIT

  • Posts: 233
sanding between primer coat
« on: December 27, 2017, 09:35 AM »
Greeting folks,
I am not a pro painter but I like painting a lot to the nice finish. I always sand between coats no mater what but just wondering if it is necessary to sand between primer to primer or put two coats of primer then sand it. I usually put two coats of primer and two coats of paint. And I am using Sherwin  Williams premium wall & wood primer on soft maple or poplar.

Thanks,

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Offline tjbnwi

  • Posts: 5684
  • Cedar Tucky Indiana
Re: sanding between primer coat
« Reply #1 on: December 27, 2017, 09:45 AM »
Necessary, probably not.

As long as you can get the second coat of primer as smooth sanding only the second coat, it should be fine.

I do sand each coat 99% of the time.

Tom

Offline RobBob

  • Posts: 1308
Re: sanding between primer coat
« Reply #2 on: December 27, 2017, 10:01 AM »
Necessary, probably not.

As long as you can get the second coat of primer as smooth sanding only the second coat, it should be fine.

I do sand each coat 99% of the time.

Tom
For sanding between coats, do you use a machine or sand by hand?

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Offline Alex

  • Posts: 5695
Re: sanding between primer coat
« Reply #3 on: December 27, 2017, 10:03 AM »
You don't sand between coats to get it smooth, you sand to make it rough. The scratches of the sanding make sure the next layer sticks better. Always sand between coats, with a grit around 180-240, I prefer this by hand but on larger surfaces a machine can be used, gently. No heavy sanding needed, just scratch it up to a nice even semi-gloss.

Offline tjbnwi

  • Posts: 5684
  • Cedar Tucky Indiana
Re: sanding between primer coat
« Reply #4 on: December 27, 2017, 10:05 AM »
Necessary, probably not.

As long as you can get the second coat of primer as smooth sanding only the second coat, it should be fine.

I do sand each coat 99% of the time.

Tom
For sanding between coats, do you use a machine or sand by hand?

Sent from my SM-G900V using Tapatalk

Both. Depends on the surface profiles. The products I use spec 240 grit. If I'm power sanding I use 320.

Tom

Offline tjbnwi

  • Posts: 5684
  • Cedar Tucky Indiana
Re: sanding between primer coat
« Reply #5 on: December 27, 2017, 10:07 AM »
You don't sand between coats to get it smooth, you sand to make it rough. The scratches of the sanding make sure the next layer sticks better. Always sand between coats, with a grit around 180-240, I prefer this by hand but on larger surfaces a machine can be used, gently. No heavy sanding needed, just scratch it up to a nice even semi-gloss.

They'll bond with or without sanding if recoated in the manufactures time frame. Some products will burn into the previous coat.

I sand to lay down the coat and flatten the surface. The tooth is a byproduct of the process.

Tom

Offline HAXIT

  • Posts: 233
Re: sanding between primer coat
« Reply #6 on: December 27, 2017, 12:24 PM »
Thanks everyone for respond and much appreciated. I love to use the festool sanding block that connects to my ct 26 and I use #220 or #320 if I use machine just like tjbnwi said but not to go crazy. I do it light to even out and hit the highs then I wipe it off and run my hand on the surface if it is smooth then I put the next coat. 

Offline Alex

  • Posts: 5695
Re: sanding between primer coat
« Reply #7 on: December 27, 2017, 03:07 PM »
You don't sand between coats to get it smooth, you sand to make it rough. The scratches of the sanding make sure the next layer sticks better. Always sand between coats, with a grit around 180-240, I prefer this by hand but on larger surfaces a machine can be used, gently. No heavy sanding needed, just scratch it up to a nice even semi-gloss.

They'll bond with or without sanding if recoated in the manufactures time frame. Some products will burn into the previous coat.

Well, if you say so. I am constantly surprised by the paints you use on your side of the pond.

Totally not recommended with the paints we use. We have to help our paints with the bonding between layers. Of course oil based is still most popular here, and if you don't sand between coats you will feel your brush slip away over the previous coat and you can easily get runners. More or less the same for our water based paints, but they don't dry up as hard and solid as the oil paints so its less of a problem there, but still exists.

An other reason I think it is best practice to sand between layers is because there will always be tiny uneven spots or specs of dust from the air in the paint. Sanding helps to smooth those out instead of building up layer after layer.
« Last Edit: December 27, 2017, 03:14 PM by Alex »

Offline aloysius

  • Posts: 278
Re: sanding between primer coat
« Reply #8 on: December 28, 2017, 11:05 PM »
Irrespective of how smooth you finish your timber before painting, the act of "whetting" the fibres of natural timbers with the first coat tends to raise the ends up sufficiently to roughen your lovely smooth finish.  I've found it desirable to "denib" these raised fibre ends after the initial coat, although I personally prefer the very softest of papers in 240-400, most usually the coarsest of the range.

Subsequent coats are usually taken back a bit with 400 between coats, just to ensure adhesion & smoothness.  The lightest of sands, particularly by hand, tends to highlight imperfections, foreign bodies, runs etc. that might otherwise be missed.  One's fingertips seem particularly sensitive to the finest of lumps & undulations that might be felt through a folded sheet of abrasive.

I've personally never bothered with any more than an initial, single coat of primer, but then again I'm not using the same type or variety of finishes either.
FOG-wit since '95:  Some say since birth...

Online Cheese

  • Posts: 4837
Re: sanding between primer coat
« Reply #9 on: December 29, 2017, 12:38 AM »
I’ve always hand sanded between primer coats because that was the norm for automotive or motorcycle finishing. Usually using a “well worn” piece of 400 wet-or-dry because that’s as good as it got before 600/800/1200 grits were invented.

Today however, I’ll shoot 2 coats of primer and then hand sand very lightly with used 320, 400 or 600 paper, just to rid the surface of dust nibs. Apply a couple of top coats and then check the smoothness again by feel and if need be, sand lightly again before applying another top coat.

I’ve found that when I machine sand between coats, I have a tendency to remove too much material. By hand sanding, you’ll remove less primer/paint and you’ll have a better sense as to how smooth the surface really is.