Replies

1. 
   DaveRicheson | Dec 14, 2006 02:04pm | #1

   Alkyd paints are manufactured from oils derived from a variety of sources. The most common being flax seed. Chemically the oils are called "short oils" because of the short molecular length  and the ability to oxidize quickly (dry in air at room temp.)

   Latex and vinyl  paints do not chemically react with oxygen in the air, but coeless to form a film as the water in them evaporates. If you look at a latex suspension under high magnification, you will see small round spheres with fuzzy edges. Kind of like a bunch of tiny rubber balls, and as the water leaves the applied film the sphere bond to each other to form a film with the pigment trapped in it.

   Back in the early days of latex and vinyl, one was cautioned to not use them over alkyd paints or primers, mostly because they could not get a good "bite" on the primer and would peel off in some conditions. Alkyds could be applied over latex because the stronger solvent line up allowed it to soften the undercoat and retain a greater degree of "intercoat adhesesion.

   Modern paint formulation pretty much have overcome all of those issues, particularly with interior products.

   Reading the label on both products should pretty much answer your question, but at first blush, I would think your plan is doable.

    

   Dave

2. 
   moltenmetal | Dec 14, 2006 03:15pm | #2

   The only place I'd use an alkyd primer any more is over bare wood or metal.  Alkyds are still king for that application.

   If by "skim coats" you mean plaster, or mud over drywall, use PVA primer.  It's a latex, very alkali resistant, and literally seals and sticks like glue- because that's basically what it is.

1. 
   rick12 | Dec 14, 2006 08:33pm | #4

   "very alkali resistant'

   Could you explain that to me and why it could or would be a benefit? I'm learning here.

1. 
   moltenmetal | Dec 15, 2006 09:47pm | #5

   Drywall mud, plaster, cement board etc. are alkaline (i.e. basic, the opposite of acidic).  Alkyd paints can be attacked by the alkali (base) and lose adhesion over time.  PVA primer stands up well to the alkali, protecting the paint above.  PVA primer is designed for use with drywall/mud, and it's not much good for anything else.

   The alkyd primer won't be absorbed as much by the drywall, so it'll give you more coverage for less work when painting.   It'll stick just fine, it seals well but it is much less alkali-resistant than the latexes so it may be attacked over time by the mud.  Alkyds are oil based- they're loaded with solvents that are bad for you long term, and they're a b*tch to clean up after.  And they're twice the price of PVA primer to boot. 

   As far as I'm concerned, bare wood is the last refuge of alkyd primer.  The modern latexes are so good that the alkyds just aren't worth the bother any more for anything else.  But the latexes will never seal bare wood properly because the water in them raises the grain.  Unless you want to sand afterward, alkyds are still king in that application.

    

   Edited 12/18/2006 7:45 am ET by moltenmetal

1. 
   DaveRicheson | Dec 15, 2006 10:38pm | #6

   Alkyd paints will also raise the grain on wood. Re. solvents.

   Wipe a piece of sanded wood with just about any solvent, and water is a solvent, and it will raise the grain.

    

   Dave

1. 
   moltenmetal | Dec 17, 2006 11:04pm | #12

   It's a matter of degrees:  water causes wood fibres to swell to a much greater extent than oil-based solvents do. 

2. 
   rick12 | Dec 16, 2006 02:25am | #9

   Thanks for your "alkali resistant" explanation. Another quick question here. The paint(flat latex) near the top of my sheetrock walls in my small bathroom continues to flake off because of my hot showers. I was once advised to use an oil primer before I paint again. I would prefer to stay with a flat finish. What do you recommend? Thanks.

1. 
   Hazlett | Dec 16, 2006 02:41am | #10

    rick,

    zinzzer makes a mildew proof bathroom paint that I think will solve your problem--- i had a similar situation in a previous house. scrape and sand it down  VERY well--patch if needed.-- I put about 5 coats of BIN on( that takes little more than an hour)

   top coat with the Zinzer mildew proof paint-----------worked VERY well--absolutely no re-occuring problems after that. It does have a bit of a sheen to it----but I really don't think you want a flat paint in a bathroom anyway.

   good Luck

   Stephen

2. 
   rick12 | Dec 16, 2006 05:08am | #11

   Thanks Stephen.

3. 
   AaronRosenthal | Dec 18, 2006 07:49am | #14

   I used Zinnser in my bathroom after I stripped 70+ years of oil paint off the walls. My mistake was not using a good primer. Never again.
   I need to re-paint, not from mildew but from peeling, and I'm going to strip the loose stuff off, and prime with a good Alkyd primer first - then topcoat with Zinnser K&B or SW K&B.Quality repairs for your home.

   AaronR ConstructionVancouver, Canada

    

4. 
   Hazlett | Dec 18, 2006 02:16pm | #17

    Aaron----did you use BIN--or the other zinzzer product ?

    I have never had ANY problem with BIN ( other than the buzzzzzzzz !)

   Stephen

5. 
   AaronRosenthal | Dec 18, 2006 10:18pm | #19

   Yes, Stephen, I have, and extensively.
   I used to paint out apartments, and routinely used Zinnser products in the bathrooms because some of them were oil and some were latex. Self-priming was really good.
   BUT, I found when I painted bare, old plaster/new drywall patch material, it is not sticking as well as it should. So, next time I'm going back to a good alkyd primer and a good anti-mildew K&B paint.Quality repairs for your home.

   AaronR ConstructionVancouver, Canada

    

6. 
   Hazlett | Dec 19, 2006 01:10am | #20

    that's good to know Aaron.

    I have used  BIN many times--- but I don't know if it's EVER been on bare plaster------ it's usually been on old walls, washed down with TSP--but still disgusting.

   On actual old plaster--if we got down to bare plaster-it would have after stripping wall paper--and I would have blamed any adhesion problems on old sizing or something.

   good to know, thanks,Stephen

7. 
   JohnSprung | Dec 19, 2006 03:32am | #21

   > I have never had ANY problem with BIN ( other than the buzzzzzzzz !)

   As they say in the software biz, that's not a bug -- that's a feature.  ;-)   

    

   -- J.S.

    

3. 
   BruceT999 | Dec 18, 2006 11:18am | #15

   "...cheap non-acrylic latex paints can be attacked by the alkali...""The alkyd primer ...it's also reasonably alkali-resistant."I'm afraid I have to disagree with you on the above statements. I worked 15 years for a paint factory that made both alkyd and latex paints, so I know that the reverse is true. Alkyd resins tend to break down when applied over alkali surfaces such as concrete. Latex paints, on the other hand, do well over concrete or stucco. After all, they are formulated with high pH levels (ie: basic, from ammonia, ethanolamine or other amines) to keep the resin emulsified in the water. You are right about PVA being best over drywall. The stuff is basically white glue with some pigment, so it's cheaper than any other primers and it wets out the drywall paper better than latex does.BruceT

1. 
   DaveRicheson | Dec 18, 2006 02:09pm | #16

   Glad you chimed in.

   I worked as a lab tech. in a product development lab for 7 years, but it was all industrial coatings. Never worked with any residential products, and left just as water soluble and powder coating were just being developed.

   Who did you work for?

    

   Dave

2. 
   moltenmetal | Dec 18, 2006 03:43pm | #18

   Thanks for that- it's absolutely correct.  I'll go back and edit my posts so that they're accurate.  The OP's whole point of starting the thread was to find out if alkyd primer was the best choice for drywall, and given your answer alkyd primer isn't a good choice due to the alkalinity.  I understand the concern about softening the drywall mud with a water-based product, but personally find that if you do a good job of dusting prior to painting it's not much of a problem.

   Just out of curiosity, given your formulation experience:  what's the major film-forming constituent in non-100% acrylic latex paints?

2. 
   JohnSprung | Dec 15, 2006 10:54pm | #7

   How about alcohol based primers?  My guess is that they'd soak in better and get a really good grab on wood.  They also block waterborne stains.  And they dry so fast that watching paint dry can be exciting....  ;-)  But what are the downsides and compatibility issues?  

    

   -- J.S.

    

1. 
   moltenmetal | Dec 16, 2006 02:02am | #8

   Yeah, I guess you could consider shellac as an alcohol-based primer of sorts.   It does a great job as a sealer, but dunno how much "bite" it provides to the top coat.  That's primer's other job.

1. 
   sharpblade | Dec 18, 2006 05:10am | #13

   Shellac based primer by zinsser has plenty of "bite" both under it and on top. Sticks to glass. BUT (and that's a big BUT) it is not recommended for large surfaces outdoors, only for "spot" priming.  I've been wanting to call the manufacturer on this and ask what exactly they mean by hat and to better understand the limitation.

   Best thing about this stuff is it can be used in VERY cold temps, I was able to prime an enclosed but not heated porch 2 weeks ago when temps in the BE were 20~40 deg F.  Also easier to clean than alkyds.

3. 
   BillBrennen | Dec 14, 2006 07:23pm | #3

   Alkyd primer is my favorite for sealing drywall mud. The solvents don't soften the mud like the water in latex does. The alkyds penetrate and consolidate the surface better than latexes in my experience, giving a more durable wall.

   I like the Zinsser Cover-Stain, which smells less wicked than Kilz (still need a respirator) and can be recoated in an hour or two with latex topcoat.

   Bill