When painting over woodwork and walls, is it better to prime it and put one/two finish coats over that or is it sufficient enough to just put two finish coats over the old paint?
Also, is it okay to clean out paintbrushes in laundry sinks when using latex paint?
Thanks!
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Replies
That depends on the condition of the existing paint. If loose or flaking, you need to scrape and sand first, then prime. If High gloss existing, you need to sand to get a mechanical bond. If greasy, sooty, dusty, you need to wash it down with TSP (Sodium Tri-Phosphate) to remove slime buildup that would interfere with bonding and to microscopically etch the surface for better bond. Rinse with clear water and dry. I almost always like to wash first because you have lots of dust and grime from living in a house that you are not even aware of. If smokers lived there, or wood heat was used, it is definitely in need of the washdown!
Primer does three things;
>>>>seals the wood/drywall so goodness isn't sucked out of the paint into the surface
>>>>>acts as a bonding agent/glue to give the finish paint a better surface to 'stick' to.
>>>>>>provides a base colour, disguising old colour that might telegraph (say if you are putting new pastel yellow over old dark blue, you'd end up with a greenish muddy yellow if there were no light beige tone or white primer first.
Dang, piffin, I'd pay you to paint my house.<g>
I agree with you 100%. I also think that prior to any repainting, the surface should be prepped with a scrubdown using trisodium phosphate.
As to the poster's question about cleaning brushes...buy top-quality brushes. When you clean them, use a brush spinner, and spin them in an empty drywall bucket. Works like a champ. Takes much less time than conventional brush cleaning, and does a much more thorough job. The brush spinner can spin rollers, too. They cost maybe $15-$20, and you'll make that back the first time you try to re-use your $40 paint brush and find that instead if it being stiff and useless with dried paint up in the ferrule from your normal hand-cleaning, it's still in primo shape.
After spinning, I put the drywall bucket outside and let the spun-out paint's carrier evaporate. Nothing ends up going down your sink.
Mongo,
Who makes a brush spinner and where can I buy one?$ Bill
Any paint store.Excellence is its own reward!
Bill,
Most of the paint stores carry them, as well as HD.
Mine is made by Shur-Line. It's the only model offered for sale around here.
I'm assuming you are talking interior painting. For almost all circumstances, to repaint a previously painted wall where the existing paint is not in an extreme condition of some kind, I would just paint one to two coats of finish.
Same on woodwork, unless prep reveals unpainted wood, in which case I spot prime.
Before washing the brush in the sink, I use a scrapper or knife to remove as much paint as possible onto a newspaper. This saves a LOT of paint down the drain. Beyond that, the best answer to this question would be received from the local sewage treatment plant.
Rich Beckman
In our area, if you being a conscientious citizen and following the "rules"; you comb/squeeze as much excess paint as you can from the brush onto brown paper which you then wrap up and eventually take to the hazardous waste disposal station. Many will spin after that. You can then wash the brush in the laundry tub.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
Just in case no one has addressed this point in your painting question: You need to determine what type of paint is already on the walls and woodwork. As you probably already know latex paint doesn't adhere very well to existing oil based paints. If you are going to be applying latex paint, determine if the existing paint is latex or not. One way to do this is to use Lacquer thinner on a paper towel, wipe it on the painted surface. If is is latex, some of the paint will come off. If not then it is probably an oil based paint. If the existing surface is latex and you are applying latex, then follow the advice that has already been given by other Breaktime folks. If the existing surface is oil based paint and you want to apply a latex paint, first clean the existing surface with TSP or soap and water, then you will need to apply something on the surface of the oil based paint for the latex paint to stick to. One product I have used sucessfully is Liquid Sander. It is a liquid you apply with a brush, let dry then you are ready to paint, after you have properly prepared the surfaces (filled holes, caulked etc.). If the exisiting surface is latex and you want to apply an oil based paint, just clean the surface, prep and start painting. Good luck. NM
Most of the info you just passed on is incorrect.
Situations like this is EXACTLY the reason so many people get SO confused when trying to find advice.
Please don't take it personally, but wrong info is just plain wrong info.
The latex on oil info is based on EXTERIOR only. Since the interior of a home is climate controlled, and since most ACRYLIC paints now are better quality than ever before, this bit of info is out dated and incorrect. The problem with applying acrylic or latex over oil based paints OUTSIDE is the difference in expansion and contraction rates for alkyd and latex paints. The latex or acrylic paints will contract and expand much more than the alkyd based, and the paint will literally let go. To solve this problem, use a premium primer/sealer/bonding agent before applying latex over alkyd (Exterior applications).
As for the Liquid Sander, it is a DEGLOSSING agent. It is SPECIFICALLY for deglossing a surface so that the paint or primer has a better surface to grab. Better yet is to use a primer/sealer/bonding agent that is specifically designed for glossy surfaces. It serves the same purpose AND adds the benefits of a primer/sealer/bonding agent all in one. It will CHEMICALLY bond itself to the existing painted surface, and chemically bond the new top coat to itself. In essence, you get a three way chemical bond (the original paint, the primer, and the top coat).
When painting a glossy surface (such as existing high gloss painted surfaces) you have three choices in order to degloss the surface, and provide a surface that the new top coat can grab on to. First choice is a liquid deglossing agent. It is messy, smelly, and a lot of trouble to mess with. Second choice is to hand sand the surface. This is ALSO messy, labor and time consuming, and is a booger bear if you are deglossing latex based paints. Third choice (and my favorite) is to use a premium primer/sealer/bond coat made SPCIFICALLY for glossy surfaces. It is fast, easy, and you get an added benefit of a primer/sealer/bond coat all in one. Makes the top coat look much better too.
Just a thought...
James DuHamel
J & M Home Maintenance Service
"The latex or acrylic paints will contract and expand much more than the alkyd based, and the paint will literally let go. To solve this problem, use a premium primer/sealer/bonding agent before applying latex over alkyd (Exterior applications)."
I am not arguing with your point here, I just want to know if you can explain why the primer/sealer/bonding agent works. If you have two layers of paint where one contracts and expands more than the other and if you bond them together, would they eventually break away from the substrate after a few hundred thermal cycling? Can you just paint oil over latex without a primer/sealer/bonding agent in exterior application? What about surfaces stained with an oil penetrating stain? Treat it the same as oil paint? I want to find out what works in the real world.
Tom
Hey Tomchark!
First of all, the reason the primer/sealer/bonding agent works so well is because it CHEMICALLY bonds the paints together. This bond, if done properly, is permanent. To do it right, the surfaces MUST be clean and sound. The chemical bond will literally meld the paints together to form a new, very solid and permanent coating (IF the surfaces were properly prepped, and IF the exisitng paint is intact and ind in good condition). The paint will not break away from the substrate if the original paint was applied correctly. The existing primer should have bonded with the wood, and the existing top coat should have bonded with the primer/selaer. If it DOES let go of the surface after several hundred thermal cycles, it was a bad paint job originally. If it is all intact and in good shape, the new top coat will be just as good, just as permanent, and just as stable as the original.
Any paint job is only as good as the surface it is applied to. If the existing painted surface is in poor condition, the new top coat will be that way in short order.
Latex or acrylic CAN be applied directly over an exisitng oil based finish (exterior), but I wouldn't do it without priming/sealing with a good bonding agent. Moisture has a good chance of getting trapped beneath the surface and breaking loose the bond. When that happens, the latex paint will literally peel right off. Same holds true for oil over latex (exterior). The moisture gets trapped between the coats, and the paint will literally bubble up, peel off, flake, and come loose. The primer/sealer/bonding agent cures this problem.
One thing to keep in mind about primers and paint - they do not dry, they CURE. Curing is a chemical reaction. Just like any other chemical reaction, the conditions must be correct for the curing action to be complete. The surfaces must be clean and dry, and the existing paint surface must be in good condition. Once cured, the new paint, the primer/sealer/bonding agent, and the old existing paint surface will blend as one. You will not be able to scrape off the new paint or the primer without taking the existing paint layer with you. If you CAN scrape them off separately, the process did not work correctly.
Just a thought...
James DuHamel
J & M Home Maintenance Service
I am thinking along the line of if you bond two things with different coefficients of expansion, something has to give eventually. Unless, the alkyd paint can somehow limit the expansion and contraction of the latex paint. The same thought came to my mind when a neighbour who was building a local light transit line told me that they clamped down the rail so well that it didn't need expansion joints.
Tom
Tom,
That's what the primer is for. It chemically bonds itself to the original paint surface. The acrylic (or latex) will then bond itself chemically to the primer. The only thing that SHOULD ever let go is the original paint from the original surface. Any paint job is only as good as the layer it is being applied to. If the original paint job is not in good shape, or the original bond between it and the original primer is not intact, then the new topcoat and primer will come off with it (if and when it decides to let loose).
It pretty much boils down to the chemical bond. The chemical reaction causes the two products to kind of "meld" together at the surface. This "melding" is permanent, and it will NOT let go, no matter how much movement variation there is between the two different products. The only thing that SHOULD ever let go is the original paint/primer from the original surface. This is why you can use oil based primers on bare wood, and top coat with acrylic or latex paints without fear of the paint failing to adhere to the primer. It is all a chemical reaction that bonds the two products together at the surface level.
Primer/sealers do the exact same thing with bare wood. They chemically bond themselves to the wood surface, penetrating the surface a bit to get a grip. Some wood species are not too good about taking paint. This is because the tannins, oils, resins, etc. in the wood interfere with the primer's ability to penetrate and "grab" the wood fibers. They make special primers for these types of woods and applications that will BETTER chemically bond with the tannins, oils, resins, etc. to form a good, strong bond.
Because primers are a chemically reactive product, they have an "active" lifespan. If you prime a surface, you have a limited time to apply a top coat. If you exceed this time frame, the primer will no longer be able to chemically bond itself to the paint surface. Each primer product will have it's time limits listed on the can. They can range from 2 weeks to 45 days. Once the time limit is expired, it is no different than applying the top coat of paint over the old topcoat of paint. There is no real adhesion, and no chemical bonding. The top coat may very well let loose in the near future.
Just a thought...James DuHamel
J & M Home Maintenance Service
One more thing James, what brand(s) of primer/sealer/bond coating for glossy surfaces do you have favorable experience with?
Tom
James,
Unfortunately the person submitting the original painting question did not specify the age of or the type of paint on the existing painted surface. Nor was the interior climate of the project every given. New latex paints are vastly superior in their qualities to accept different types of paint. That is a given fact. But since the Breaktime audience doesn't know all these facts and perhaps even the original inquirer doesn't either. It always pays to take all precautions. I have learned from experience (especially in older homes) that some interior oil base painted surfaces will not take latex paints unless certain steps are taken to prepare the wood. In this original Breaktime question, cleaning the surfaces, deglossing them, priming or sealing them, (and these two steps might be done in one step with the all in one product like what you mentioned, a deglossing. sealing, primer) sanding and other prep steps always lead to a smooth surface that is ready for the finish coats of paint. Shortcuts can lead to customer call backs. Hopefully everyone's input has not confused the initial question.
I agree with what James has to say but in addition to the chemical bonding from using the right primer, the etching of TSP or of sandpaper will cut tiny microscopic grooves in the old surface. That provides a mechanical as well as the chemical bond - like thousands of tiny fingers holding on for dear life to the face of a cliff.
Excellence is its own reward!
James has laid this out very well. Primers are an important part of the painting process and are not simply "cheap paint", as some people believe.
From my knowledge, you can apply a latex over an oil, provided that there are not too many layers of oil paint on the existing surface. Putting oil over a latex, even with the help of a primer, is questionable in my opinion. I just don't see the advantages of doing that, and you may just be causing trouble for yourself later on.
All quality paint manufacturers make good primers. Sherwin Williams, Ben Moore, Behr, Pratt & Lambert, etc have primers designed to work with their paints. My favorate generic primer would probably be Zinsser's Bullseye 1-2-3. Not a huge fan of Kilz, but it is a great product in certain applications.
I use primer probably more than I have to, but it is your insurance policy for a quality paint job. If I am repainting an interior wall with flat or eggshell covering flat or eggshell, I don't prime. If its the first time a house has been painted since it was built, then I prime to seal the wall surface. When in doubt, use a primer.
Eric