Sanding A Long Oil Primer - Painting - DIY Chatroom Home Improvement Forum
Advertisement


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Painting

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 04-28-2015, 03:18 AM   #1
Member
 
Join Date: Sep 2012
Posts: 114
Rewards Points: 232
Default

Sanding a long oil primer


Any advice for sanding a long oil primer? Damn thing never seems to dry. Gums up sandpaper, bits still mushy after a week.

Advertisement

halliwellc is offline   Reply With Quote
Old 04-28-2015, 06:41 AM   #2
Member
 
Join Date: Sep 2012
Location: outside ocala fl
Posts: 4,364
Rewards Points: 3,764
Default

Sanding a long oil primer


Will not sand until completely dry. Maybe a fan will aid in drying. A little more info may help also, what primer, on what surface, how applied may help in an answer.

Advertisement

__________________
Entering your general location can help with answering a lot of times
ToolSeeker is online now   Reply With Quote
Old 04-28-2015, 11:04 AM   #3
Member
 
Join Date: Sep 2012
Posts: 114
Rewards Points: 232
Default

Sanding a long oil primer


Quote:
Originally Posted by ToolSeeker View Post
Will not sand until completely dry. Maybe a fan will aid in drying. A little more info may help also, what primer, on what surface, how applied may help in an answer.
Benj Moore long oil "Fresh Start Moorwhite" applied to sound, bright, scraped and sanded 100-year-old window sash in workshop in 60-degree weather. Tulsa, OK humidity, rain every few days.

I use the long oil for penetration, but after three days...come on, it's not penetrating any more. Harden up already.

Hot box? Dehumidifying box? Sunlight? After-wipe-on curing accelerant? I don't want to using drying agents to start with, would lose the whole point of long oil.
halliwellc is offline   Reply With Quote
Old 04-28-2015, 01:38 PM   #4
Member
 
Jmayspaint's Avatar
 
Join Date: May 2013
Posts: 1,650
Rewards Points: 500
Default

Sanding a long oil primer


Try wet sanding it. A damp cloth and some 400 wet/dry might just do the trick. If not with water, maybe some spirits.
Jmayspaint is online now   Reply With Quote
The Following User Says Thank You to Jmayspaint For This Useful Post:
ToolSeeker (04-28-2015)
Old 04-28-2015, 09:47 PM   #5
Member
 
Join Date: Jun 2008
Posts: 1,576
Rewards Points: 1,124
Default

Sanding a long oil primer


Quote:
Originally Posted by halliwellc View Post
Any advice for sanding a long oil primer? Damn thing never seems to dry. Gums up sandpaper, bits still mushy after a week.
Woodworkers will use something called a "sanding sealer". This is a clear coat that's meant to be sanded smooth. When bare wood is first varnished, all of the loose wood fibers will stick up, and the whole idea behind using a sanding sealer is to sand that first coat smooth so that the glitches in that first coat don't get inherited to each subsequent coat.

But, I've never heard of sanding an alkyd primer smooth. Maybe if you can explain the reason for doing this it would help. Primers are meant to dry to a matte finish so that the top coat of paint sticks better. You won't get any better paint adhesion by sanding your primer.

I'd probably use a hair dryer to warm up that primer. The cool 60 degree temperatures may be what's keeping it from drying.

Also, the whole idea behind sanding a surface for better paint adhesion is that it increases the surface area the paint has to stick to. But, you don't always get better paint adhesion as a result of sanding. The primer will dry rough enough to provide plenty of surface area for the paint to stick well.

That is:

wwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww

is smoother than:

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

but because they both have the same surface area, paint would stick equally well to both surfaces.

I'm wondering if you're sanding your primer because you think it will improve the paint adhesion?
__________________
Bashing my head against the walls in some of the internet's finest chat rooms.

Last edited by Nestor_Kelebay; 04-28-2015 at 09:59 PM.
Nestor_Kelebay is offline   Reply With Quote
Old 04-29-2015, 07:25 AM   #6
Member
 
Join Date: Mar 2015
Posts: 302
Rewards Points: 604
Default

Sanding a long oil primer


Sanding an alkyd primer on interior wood is the norm from what i have seen. Primarily to provide a smoother surface. On an exterior alkyd it isn't really necessary unless you are trying get a super smooth look. But on an exterior I would think the adhesion would be more important, therefore I would think the coarser surface profile would be better. This is one reason you are supposed to etch concrete floors before you paint them. Much better adhesion.
klaatu is offline   Reply With Quote
Old 04-29-2015, 09:54 AM   #7
Member
 
Join Date: Mar 2015
Location: Northern Virginia, United States
Posts: 78
Rewards Points: 156
Default

Sanding a long oil primer


You sand primer smooth to get the brush marks out on trim, which range from barely noticeable (B-I-N) to hideous, looks-like-it-was-applied-with-a-witch's-broom-and-laid-off-with-a-rake (I'm looking at you, Cover Stain). Outside, I probably wouldn't bother, but the OP wants a smooth finish.

I haven't used that BM primer, but have used Sherwin's similar exterior long oil. In general, if an alkyd goes on too thick, it will take a very long time to cure. The reason for this is that alkyds (oil paints) cure by oxidation. If the film is too thick, oxygen can't efficiently penetrate the whole depth of the film to finish curing the resin. The recommended wet film thickness for your BM primer is only 3 mils, which is really pretty thin. Given that it's 66% volume solids, I assume it is very viscous, and probably drags the brush, assuming that's what you used, pretty badly. SW's exterior oil is 'only' 54% volume solids, and it takes some effort to spread with a brush. So, I bet it's on there too thick, and that, coupled with temps in the 60s, is slowing the cure down.

BM 100 TDS:
http://www.benjaminmoore.com/Downloa...tds%2FTDS_0100

That's for future reference. For your current situation, wet sanding as suggested above by JMays sounds like a plan. Or maybe Abranet?

Last edited by CyrusR; 04-29-2015 at 10:00 AM. Reason: 'is' for 'are'
CyrusR is offline   Reply With Quote
Old 04-29-2015, 08:19 PM   #8
Member
 
Join Date: Jun 2008
Posts: 1,576
Rewards Points: 1,124
Default

Sanding a long oil primer


Quote:
Originally Posted by klaatu View Post
Sanding an alkyd primer on interior wood is the norm from what i have seen. Primarily to provide a smoother surface. On an exterior alkyd it isn't really necessary unless you are trying get a super smooth look. But on an exterior I would think the adhesion would be more important, therefore I would think the coarser surface profile would be better. This is one reason you are supposed to etch concrete floors before you paint them. Much better adhesion.
I dunno. Sanding down a primer is a new one on me.

The whole idea behind sanding a surface before painting it is to make it rougher. Why? Because a rougher surface has more surface area for the paint to stick to, thereby increasing the apparent adhesion. The paint still sticks to the surface with the same force per square inch, but sanding increases the number of square inches.

Primer dries to a rough surface to begin with, and that roughness serves to increase the surface area of the primer... for better adhesion. Who ever said that sanding a primer would increase it's surface area? You might even be reducing the surface area by sanding the primer.

If the idea in sanding the primer is to get rid of brush strokes, then the correct fix is to thin the primer more before applying it, or stop brushing sooner. You want the primer to be liquid enough to flow and self level BY ITSELF. Too often people keep trying to make it smoother with a brush until the primer is too thick to self level by itself.

As was mentioned in a previous post on this thread, alkyds cure by reacting with oxygen. That's a chemical reaction, and therefore very subject to temperature. The cool ambient temperatures (mid-60's) would definitely be a reason for the primer to be slow to "dry". Moving the window to a warmer place would help that chemical reaction speed up.
__________________
Bashing my head against the walls in some of the internet's finest chat rooms.

Last edited by Nestor_Kelebay; 04-29-2015 at 08:22 PM.
Nestor_Kelebay is offline   Reply With Quote
Old 04-30-2015, 07:42 AM   #9
Member
 
Join Date: Mar 2015
Posts: 302
Rewards Points: 604
Default

Sanding a long oil primer


Quote:
Originally Posted by Nestor_Kelebay View Post
I dunno. Sanding down a primer is a new one on me.

The whole idea behind sanding a surface before painting it is to make it rougher. Why? Because a rougher surface has more surface area for the paint to stick to, thereby increasing the apparent adhesion. The paint still sticks to the surface with the same force per square inch, but sanding increases the number of square inches.

Primer dries to a rough surface to begin with, and that roughness serves to increase the surface area of the primer... for better adhesion. Who ever said that sanding a primer would increase it's surface area? You might even be reducing the surface area by sanding the primer.

If the idea in sanding the primer is to get rid of brush strokes, then the correct fix is to thin the primer more before applying it, or stop brushing sooner. You want the primer to be liquid enough to flow and self level BY ITSELF. Too often people keep trying to make it smoother with a brush until the primer is too thick to self level by itself.

As was mentioned in a previous post on this thread, alkyds cure by reacting with oxygen. That's a chemical reaction, and therefore very subject to temperature. The cool ambient temperatures (mid-60's) would definitely be a reason for the primer to be slow to "dry". Moving the window to a warmer place would help that chemical reaction speed up.
I'm not arguing the point that one of the purposes of primer is to provide a proper surface profile for adhesion, just that in different applications it is desirable to sand it to provide for a smoother finish. For example some primers are used to fill small grain voids and surface imperfections on wood, interior trim, cabinets, and painted furniture for example. While the solids in a primer aren't adequate to provide a great amount of fill, they are adequate for most jobs. They also provide a much easier material for sanding as opposed to the topcoat. On industrial applications, such as coating steel beams, it is more important for the primer to be rust resistant and to provide the superior surface profile for adhesion. That is the main reason there are so many different primers available in the first place. And why paint AND primer AND sealer in one is a bold faced lie.
klaatu is offline   Reply With Quote
Old 04-30-2015, 11:27 AM   #10
Member
 
Join Date: Mar 2015
Location: Northern Virginia, United States
Posts: 78
Rewards Points: 156
Default

Sanding a long oil primer


Quote:
Originally Posted by Nestor_Kelebay View Post
I dunno. Sanding down a primer is a new one on me.
It's a thing.

MPI Spec for solvent-based enamel undercoaters:

http://www.specifypaint.com/APL/pain...r.asp?ID=46000
MPI # 46 Undercoat, Enamel, Interior
A solvent based, pigmented coating for interior smooth wood and previously painted plaster or gypsum wallboard surfaces to be subsequently coated with latex or alkyd finish coat(s). Has low porosity (i.e. High hold-out) and good sanding properties for semi-gloss and gloss enamel finishes.

[Evaluated characteristics include consistency/viscosity, dry time, fineness of grind, hiding power by contrast ratio method, reflectance, sanding properties, flexibility, and sealing properties. See MPI 'Detailed Performance' Specs for complete details and specific requirements.]

emphasis mine
Paint talkers talking about sandable latex primers:
http://www.painttalk.com/f2/most-san...-primer-19202/

Scott Burt on SW Wall and Wood:
http://topcoatreview.com/2011/07/sherwin-williams-wall-and-wood-primer-on-poplar/
Notice the emphasis on sanding.


'Jack Pauhl' sanding primers on poplar samples:
http://www.youtube.com/watch?v=Pwjy8OwLN-c


There are primers with sanding mentioned in the product name:

SW 'Easy Sand':
http://www.sherwin-williams.com/pain...y-sand-primer/

C2 Sandable Acrylic Primer
http://c2paint.com/products/sandable-acrylic-primer


Quote:
If the idea in sanding the primer is to get rid of brush strokes, then the correct fix is to thin the primer more before applying it, or stop brushing sooner. You want the primer to be liquid enough to flow and self level BY ITSELF. Too often people keep trying to make it smoother with a brush until the primer is too thick to self level by itself.
I wish, but some primers don't level out brush marks with any reasonable amount of thinning. Cover Stain, for instance. Wall and Wood is another, though it's better in that respect than Cover Stain. BM 217 has disappointed me, too. I was expecting much better leveling. Adding paint thinner hasn't helped. Anyway, even the best don't flow and level like good trim paints, and will still require some sanding.

Advertisement

CyrusR is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
If you use a primer, can you save money? bobjax Painting 24 05-22-2014 07:02 AM
Base color coat sticking better then primer? konsole Painting 8 08-22-2012 06:12 AM
How long does pva primer last in can? dfrey Painting 6 08-19-2012 11:06 AM
Breaking up a long/continuous wall tigereye Interior Decorating 4 03-08-2009 03:43 PM




Top of Page | View New Posts