sanding between primer coat

[HAXIT]

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,

 

[tjbnwi]

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

 

[rljatl]

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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[AlexThePalex]

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.

 

[tjbnwi]

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

Tom

 

[tjbnwi]

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

 

[HAXIT]

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. 

 

[AlexThePalex]

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.

 

[aloysius]

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.

 

[Cheese]

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.

 

[Mate]

What Festool sander would you recommend for sanding primer and paint between coats?

I have 6 indoor doors to prepare and paint in my house and I will do some furniture in future so I would like to do it with power sander.

right now I have Bosch 18V random orbital sander but it is to aggressive for primer sanding - I used it on speed 3 (of 6) and 320 grit sand paper.

so I hope Festool have something good for doors and furniture sanding.

thanks.

 

[jeh]

I with limited exceptions always sand after the primer dries. Depending on what it is I might do a light scuff sand areas that are not glass smooth after the 1st finish coat. That is hand sand only as you don't want to heat up the paint.

 

[Packard]

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.

For clear finishes, I use Sealcoat as a primer.  I lightly sand with 400 grit to get rid of the dust nibs and for improved adhesion.  Sealcoat does not require sanding for good adhesion with additional coats.  So that sanding is just for the dust nibs.

I use clear poly, either brush on or wipe on.  And I always sand for both the dust nibs and  adhesion.

A shellac based primer (B-I-N, for example) will not raise the grain and sanding after the primer is much less work.  I only put down one coat of primer.  The only purpose for primer is adhesion.  As long as I have coating integrity (no gaps in the coating), I can see no purpose in multiple coats of primer.

Unfortunately, my favored cabinet paint (Benjamin-Moore’s Advance) sometimes gets a crackle like effect going over shellac.  So I first put down Sealcoat (so I don’t have to deal with raised grain) and then put down a pigmented water based primer (usually 1-2-3).

 

[Packard]

If your concern is adhesion, then there are kits for testing for this.  They consist of a device to make cuts in the finish in a cross-grid, and then using highly-uniform adhesive tape to try and pull up the small squares in the grid. 

For me, adhesion is going to be the #1 factor that I look for.  Nothing ruins a paint job more than flaking paint.

For paint manufacturers and production paint shops with a Q.C. (Quality Control/Quality Assurance) department, these kits are necessary. 

For my purpose, I take a utility knife with a new blade and cut a grid yielding small squares about 3/16” across.  I then place conventional masking tape over the grid and burnish it down, and then I lift the tape to see if the little squares lift with it.  If adhesion is good, the squares will remain on the painted surface.

To my satisfaction, I found that the combination paint/primer adheres better than plain paint, and primer then paint adheres substantially better yet. 

You can get the kit for more accurate results.  They range from $40.000 to $250.00 for the kits. 
https://www.google.com/search?q=paint adhesion test kit&ie=utf-8&oe=utf-8&client=firefox-b-1-m

I would note that mineral pigments are reputed to more fade resistant than other pigments.

And adhesion does not address durability of the finish, though poor adhesion will define poor durability.

The paint on my garage doors (Behr Marquis) faded badly and got chalky.  It did not flake, but still, not a good result.

 

[Redromad]

I too prime twice and paint twice. I sand between each coat progressively getting more fine. 120, 150, 220, 320

 

[Huey52]

I too Sealcoat (dewaxed/thinned shellac) as the primer; one or two coats as necessary. Then two or three topcoats. As others have well cited only light sanding 220/240 to remove nibs and the fine sanding scratches as a byproduct promote adhesion. A remarkably smooth final finish may be achieved if you sand lightly between coats and also the final.

Of course remove any sanding debris prior to the next coat. Although I paint in a very air-clean environment there are still most always some nibs.