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-   -   Advice needed on paint prep... (http://www.houserepairtalk.com/f107/advice-needed-paint-prep-7529/)

myke232 09-09-2009 01:30 PM

Advice needed on paint prep...
 
I am in the process of prepping the interior of a closet for painting. The existing paint on there now is oil based and probably put on sometime in the '70s (although I'm not positive of exactly when).

Anyway, there were some areas where it was scraped off a bit (I think where clothes would rub against it). When I went to sand/degloss I found that some of the paint will flake off under not mush pressure; however, it's not peeling at all. I have attached pics to see what I'm talking about; I think that is primer beneath the paint, but I'm not positive.

My question is, can I wash with TSP and then prime at this point? Or will it all be for not, and the paint will start to peel or flake eventually? If it's not ready to prime at this point, what are my options?

Also, I attached another pic of some of the trim. I sanded this down a bit, and plan to wash with TSP and then prime. What do you think, is it ready for that?

Thanks a lot for your help!

http://www.diychatroom.com/attachmen...-picture-2.jpg

http://www.diychatroom.com/attachmen...-picture-1.jpg

http://www.diychatroom.com/attachmen...-picture-3.jpg

http://www.diychatroom.com/attachmen...-picture-4.jpg

Nestor_Kelebay 09-09-2009 06:24 PM

Are you sure that beige top coat is an oil based paint?

Normally when you see poor adhesion like that, it's when a latex paint has been applied over a high gloss oil based paint. However, it could also be poor adhesion for some other reason, such as the wall being dirty (with cooking oil, say) when it was painted.

I'd try scraping in various places and see if there's poor adhesion everywhere or just in that one area.

Take some nail polish remover on at piece of toilet paper and see if you can clean the beige paint off the orange paint underneath. If you can, then the beige is a latex.

What you've got is basically just poor adhesion between the top coat of paint and the paint under it. Anything you do now is only going to affect the top coat of paint, not the coat under it and adhesion between the two. It would have been better if that bottom coat was sanded before being painted over, but that's water under the bridge now.

The option of trying to remove the existing top coat is a hard, time consuming and messy one. What most people would do would be to clean and roughen the walls and just paint over what you have.

How big a closet is it? Ideally, it'd be best to remove that top coat of paint, but I can see how most people would want to avoid doing that.

Try this: Stick some wide (2 inch wide Scotch tape) to the wall and see if you can take the top coat of paint off by pulling the Scotch tape off.

myke232 09-10-2009 07:52 AM

Quote:

Originally Posted by Nestor_Kelebay (Post 34475)
Are you sure that beige top coat is an oil based paint?

Normally when you see poor adhesion like that, it's when a latex paint has been applied over a high gloss oil based paint. However, it could also be poor adhesion for some other reason, such as the wall being dirty (with cooking oil, say) when it was painted.

I'd try scraping in various places and see if there's poor adhesion everywhere or just in that one area.

Take some nail polish remover on at piece of toilet paper and see if you can clean the beige paint off the orange paint underneath. If you can, then the beige is a latex.

What you've got is basically just poor adhesion between the top coat of paint and the paint under it. Anything you do now is only going to affect the top coat of paint, not the coat under it and adhesion between the two. It would have been better if that bottom coat was sanded before being painted over, but that's water under the bridge now.

The option of trying to remove the existing top coat is a hard, time consuming and messy one. What most people would do would be to clean and roughen the walls and just paint over what you have.

How big a closet is it? Ideally, it'd be best to remove that top coat of paint, but I can see how most people would want to avoid doing that.

Try this: Stick some wide (2 inch wide Scotch tape) to the wall and see if you can take the top coat of paint off by pulling the Scotch tape off.

Thanks for your time.

I'm sure the top coat is oil, because the previous home-owner left the can here (that is also how I know it doesn't contain lead, as nothing on the can indicates that).

As far as the adhesion, it is worse in the areas where the paint is already flaking off, but I don't think it's great anywhere in the closet (although it's only flaking in those particular areas).

I did the tape thing. I used masking tape about 6" long and did it in 2 areas, once where there was no flaking at all, and once right over the flaking area. The one were there was no flaking pulled of just a tiny bit of paint, in total about the size of a quarter. The second one over the already flaking area, resulted in paint all over the piece of tape.

Well, the closet is small, but yeah, I really don't want to strip all the paint out of there as that would be a tough job. I guess I could wash, prime and paint and if there are problems with it down the road I could do it at that time. Although, I'd really like to do it right the first time!

What do you think of that pic of just the trim? Does that look ready for washing and priming, or is more de-glosssing necessary?

myke232 09-10-2009 01:48 PM

Ok, I just tested for lead with the Homax Lead Check kit, and everything came back with no lead.

So, 2 questions:

1) Is the trim de-glossed enough at this point to prime (last pic)

2) What to do now with the interior of the closet? (first 3 pics)

handyguys 09-10-2009 02:45 PM

Nestor gave some good advice.

Quote:

Originally Posted by myke232 (Post 34517)
Ok, I just tested for lead with the Homax Lead Check kit, and everything came back with no lead.

So, 2 questions:

1) Is the trim de-glossed enough at this point to prime (last pic)

Yes, just make sure any residual dust is cleaned off and its dry. I use TSP to wash down the surface before painting. Make sure its dry before you begin.

Quote:

Originally Posted by myke232 (Post 34517)
2) What to do now with the interior of the closet? (first 3 pics)

The likely original issue with poor adhesion was that no prep was done. A simple washing of the wall would have likely avoided the issue you have now. The right way to do this is to remove all loose paint. Wash with TSP and then paint. Prime first if you are down to bare substrate.

Personally - I wouldn't go crazy and use a chemical stripper. I would probably just use sandpaper, wire brush and/or a paint scraper. If you walls get too chewed up then a skim with drywall joint compound, prime and paint.

myke232 09-10-2009 05:20 PM

Quote:

Originally Posted by handyguys (Post 34518)
Yes, just make sure any residual dust is cleaned off and its dry. I use TSP to wash down the surface before painting. Make sure its dry before you begin.

Nice. Yeah, I plan on washing with TSP, then using BM Fresh Start Latex Primer (or Kilz2 perhaps?), then latex paint.

Quote:

Originally Posted by handyguys (Post 34518)
The likely original issue with poor adhesion was that no prep was done. A simple washing of the wall would have likely avoided the issue you have now.

Those bastards!

Quote:

Originally Posted by handyguys (Post 34518)
The right way to do this is to remove all loose paint. Wash with TSP and then paint. Prime first if you are down to bare substrate.

Do you mean just the loose paint around the current flaking areas, or do you mean the entire surface of the interior? Also, I planned on priming everything regardless of being down to paint/substrate etc. Is this ok?

Thanks for your help!

Nestor_Kelebay 09-10-2009 10:40 PM

Several comments:

Cleaning with TSP will only dull the gloss of OIL BASED paints. TSP has no effect on latex paints. If you're cleaning latex paints, you're better off to use a decent cleaner like Mr. Clean or Fantastik to clean the wall with.

If you can get the paint off the wall with masking tape, then I'd invest in a 2 inch wide roll of Scotch tape (called "packaging tape") that has a stronger tack and will pull that paint off the underlying oil based paint.

With respect to Handyguys opinion, I have trouble understanding why an interior closet wall would get dirty and need cleaning. I could see cooking grease accumulating over a stove in a kitchen or something, but why would a closet wall get so dirty that paint wouldn't stick. I'm thinking this is just a case of one oil based paint not sticking well to a high gloss oil based paint.

Hard to tell from the pic if the trim is ready for painting. I still see a glossy reflection off the paint on it, and that's bad news. If it's an oil based paint on that trim, I'd mix up a concentrated solution of TSP and try cleaning it with that. Wear rubber gloves. Always, always, always rinse your TSP off thoroughly and allow time for the wall/ceiling to dry before you paint.

You're getting different opinions, but that's because all of us have had different experiences. The one thing we all agree on is that the lack of adhesion between the paint in your closet and what's underneath is a problem you won't be able to fix by just painting over it. But, it won't be any worse of a problem than you're having now.

myke232 09-11-2009 08:41 AM

Thanks for all of the info.
Quote:

Originally Posted by Nestor_Kelebay (Post 34533)
If you can get the paint off the wall with masking tape, then I'd invest in a 2 inch wide roll of Scotch tape (called "packaging tape") that has a stronger tack and will pull that paint off the underlying oil based paint.

Interesting, I'll have to consider that now, although at this point I was resigned to try sanding/smoothing the flaked areas again, then sand and TSP the entire interior, as opposed to trying to remove the entire top coat.

Quote:

Originally Posted by Nestor_Kelebay (Post 34533)
I'm thinking this is just a case of one oil based paint not sticking well to a high gloss oil based paint.

Totally agree. (I think Handyguy was just giving general examples of what could cause this to happen).

Quote:

Originally Posted by Nestor_Kelebay (Post 34533)
Hard to tell from the pic if the trim is ready for painting. I still see a glossy reflection off the paint on it, and that's bad news. If it's an oil based paint on that trim, I'd mix up a concentrated solution of TSP and try cleaning it with that. Wear rubber gloves. Always, always, always rinse your TSP off thoroughly and allow time for the wall/ceiling to dry before you paint.

Yeah, I think it needs more work. I plan to sand everything again, then wash with TSP.

Also, after all the prep, I plan to prime with BM Fresh Start (latex primer, but from what I have learned, it will work great over an oil paint as long as the oil is de-glossed).

Nestor_Kelebay 09-11-2009 09:26 PM

Quote:

Originally Posted by myke232 (Post 34569)
at this point I was resigned to try sanding/smoothing the flaked areas again, then sand and TSP the entire interior,

Quote:

Yeah, I think it needs more work. I plan to sand everything again, then wash with TSP.
You don't need to sand AND wash with TSP. One or the other is fine.

Quote:

Also, after all the prep, I plan to prime with BM Fresh Start (latex primer, but from what I have learned, it will work great over an oil paint as long as the oil is de-glossed).
Any paint will stick well to an oil based paint if that oil based paint is deglossed.

You should know that TSP was historically used as a cleaner for cleaning walls prior to painting because it deglosses drying oil based paints, which are paints that use a drying oil like boiled linseed oil or Tung oil as the binder. TSP should also degloss real varnish, which is nothing more than plant resins (called "copals") dissolved in drying oils like linseed oil and Tung oil.


You don't need to know the rest, but it explains why I expect a strong concentration of TSP SHOULD degloss alkyd paint (and even alkyd based polyurethane) as well:

All animal fats and vegetable oils (and even animal oils like whale oil) are "tryglycerides", which means that they consist of three "fatty acids" all connected to a glycerine molecule:

http://www.scientificpsychic.com/fit...iglyceride.gif

In the above depiction of a tryglyceride, there are three fatty acid hydrocarbon chains connected to a glycerine molecule. The glycerine molecule is the one on the right hand side that looks like this:

http://www.scientificpsychic.com/fitness/glycerolv.gif

Now, notice that the two upper fatty acid hydrocarbon chains each have a carbon atom double bonded to another carbon atom? Well, when that happens, then the oil molecule is said to be "unsaturated" because it's possible to add more hydrogen atoms to it. And, those instances of double bonds between carbon atoms are called "unsaturated sites".

Now, when plant oil or animal oil molecules contain a lot of those unsaturated sites, then there's the strong possibility that there will be instances where two unsaturated sites will be in close proximity. When you have two unsaturated sites close by one another, then an O2 molecule from the air will react if it passes close to those unsaturated sites. It will break up into two Oxygen atoms, and each Oxygen atom will react with both unsaturated sites to form a pair of C-O-C crosslinks between the two former unsaturated sites.

Linolenic acid is the fatty acid found most commonly in linseed oil, and it consists of a hydrocarbon chain 18 carbon atoms long with three unsaturated sites in it. So, linseed oil contains lots and lots of unsaturated sites, and when it's exposed to air, it gradually forms those C-O-C crosslinks inside it connecting linseed oil molecules together. The more crosslinking that occurs, the more and more the liquid oil gets thicker and thicker and starts to behave more like a solid than a liquid. Eventually, linseed oil will solidify into a solid as Oxygen molecules from the air spot weld the linseed oil molecules together over time. That process is called "auto-oxidation".

Nowadays, you can no longer buy boiled linseed oil based paints. Nowadays, the only "oil based" paints sold are "alkyd paints". So, what's an "alkyd paint"?

Based on the last few paragraphs, we know that it's those unsaturated sites in plant oil molecules that react with oxygen in the air to gradually transform the liquid oil into a solid, and hence a film of oil on a wall into a solid decorative coating. There are several oils that do that, including linseed oil, Tung (or Chinawood) oil, Safflower oil, Poppy seed oil, Walnut oil and others. Even some oils harvested from fish have enough unsaturated sites to form high quality paint binders.

To make an alkyd resin, what we do is take the fatty acid chains off the triglyceride molecules and through the miracle of modern chemistry, artificially increase the number of unsaturated sites on those fatty acids. But, since we can do that, we don't need to start with an expensive oil like linseed or Tung oil. We can take a cheap plentiful oil like soy bean oil or corn oil, strip off the fatty acid chains, and pump them up on steroids so that they're bristling with unsaturated sites.

Then we take a synthetic resin called "phthalic anhydrite" (which literally means (what you need to add water to to make naphthalic acid, so in simple terms, Kool-Aid crystals might be thought of as "Kool-Aid anhydrite").

And, finally, we add glycerine, which is the small molecule seen drawn above.

And we mix all three in a pot and bring to a boil.

All three of those chemicals will react with the other two, and the result is "clumps" of souped up fatty acid molecules held together with phthalic anhydride and glycerine molecules, and it looks something like this:

http://web.mst.edu/~jstoffer/CHEM381/glyphthal.gif

where those things that look like crabs are the phthalic anhydride molecules, the short C-C-C chains are the glycerine molecules and those -[CH2]n- things are the souped up fatty acids.

Typically, and alkyd resin will consist of 20 to 30 souped up fatty acids in "clump" held together with the phthalic anhydride and glycerine. We dissolve those alkyd resins in mineral spirits, add coloured pigments for colour and opacity, extender pigments to lower the gloss and increase opacity, and the result is called "alkyd paint".

When you spread alkyd paint on a wall, the first thing that happens is he mineral spirits evaporate. Then, O2 from the air starts to get absorbed into the gazillions of alkyd resins that form a film all over the wall, and the weight of that paint starts increasing because of the absorbed O2 molecules. That auto-oxidation process rapidly increases in speed because of the huge number of unsaturated sites, and so many of them in close proximity. It's that high number of unsaturated sites in the alkyd resins that allow modern alkyd paints to dry much faster and to a much harder film than their old linseed oil counterpart paints did. A modern alkyd paint will be dry to the touch in a few hours as opposed to a few days, and will crosslink much more densely, and that manifests itself in much higher hardness.

But, because both dried linseed oil based paint and dried alkyd paint consists mostly of plant oil fatty acids that have crosslinked together, using TSP to clean dry alkyd paint SHOULD degloss it just like a drying oil based paint. It may take a higher concentration of TSP tho.

Chem 381- CHAPTER THREE- Third Part


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