Applying Latex over Oil Base

[LG63]

I’m preparing to paint a steel overhead garage door. It has a coat of oil base, about 10 years old, over the factory finish. The existing paint is simply faded, no peeling problems. I would like to paint it with latex and was wondering about the proper prep. A lot of latex paints recommend washing the surface with TSP. So my first question: Is there anything special about TSP or will a good detergent (like Simple Green) work? Second question: Should I prime with a latex primer or just use the top coat right over the oil base.

On a related note, I tried to search “TSP” here on GJ but like every other time I’ve tried to search with an acronym, it turned up no results. Is there a way to trick the search function into handling acronyms?

 

[Big-Foot]

Washing with a TSP or TSP substitute will gt it super clean even to the point of etching. I would go that route and still hit it with a good exterior primer to ensure good adhesion.

You didn't mention if you were changing colors but priming the painting should get it done right.

 

[LG63]

You didn't mention if you were changing colors but priming the painting should get it done right.

No color change, which is why I was thinking not to prime since white primer would be more difficult to cover. I was considering giving it one heavy top coat and calling it good.

 

[Beaumont67]

Use a latex primer first (you will be fine)...always easier to apply acrylic oil over water base latex.
- with 35 years of painting, I have switched from Para, to Benjamin Moore to Home Depo's brand
- Behr Premium plus primer, covers great (their 2 gal pail is a lot cheaper than the one gallon size)
- I prime in 2 coats (sand the walls first with 120-150 grit, and vacuum walls next) and use 2 topcoats usually
I don't even want to try the new all-in-one latex paint, with primer included...some love it & others hate it.

PS - if tinting primer for fresh bare drywall, I use 1/2 the finish color formula or just use white
- never change from oil to latex, without sanding & priming first...its a big no-no, in the trade
(like trying to repaint a car over a fresh wax job...lol)

 

[Norcal]

You need a good primer to bond to the oil based finish, you could have the primer tinted to match the finish coat, if it does not bond properly you will be fighting the results for a long time.

 

[Big-Foot]

No color change, which is why I was thinking not to prime since white primer would be more difficult to cover. I was considering giving it one heavy top coat and calling it good.

Have the primer tinted.. It's done frequently according to my paint store..

 

[csp]

You need four characters to search. Add an asterisk as a wild card character to get it to four characters. TSP*

 

[jvitez]

Save yourself some work. Wash it well with TSP, rinse well and let dry. Paint it with an exterior oil top coat. If you're not changing colour and the paint is adhering well, why add more work? Oil paints will be gradually phased out at some point so use it while you can and save a bunch of work.

If the paint is smooth, then no need to sand. Just use TSP as it degreases and gives the paint some tooth for the topcoat to bite.

 

[LG63]

Save yourself some work. Wash it well with TSP, rinse well and let dry. Paint it with an exterior oil top coat.

I may reconsider oil base. I’ve always used oil base on metal doors in the past but these days the guys at the paint store look at you like you’re from Mars when you ask for oil base. I guess I’ve heard the pitch “modern latex is just as good or better than oil base” so many times I started believing it.

 

[Tim The Tool Man]

I don't mean to offend anyone on this thread but applying latex over oil primer is fine and totally acceptable. If the base-coat is an oil finish coat then you would want to prep the surface first. TSP and a good scuffing with a green 3M scotch type pad are fine for this step. I would then apply a quality latex top coat and be done. You can also prime it first with a decent quality latex (or oil) as long as there is no bare metal. ..and yes you can have the primer tinted for free at your paint supplier. I have a preference to Sherwin Williams brand, never had any problems with it.

That being said you stated that this is an overhead door, paint is heavy, latex more so than oil. Were it me I would stick to oil and then re-adjust my springs.

 

[evildky]

TSP = Tri Sodium Phosphate, sold in boxes at any hardward paint department or part store, it's a paint cleaner, Dirtex works really well in powder form but harder to find

If you're real worried abotu adhesion, Kilz oil base primer sticks to anything and everything sticks to it!

 

[rlitman]

Oil paints will be gradually phased out at some point . . .

Not really. Oil based paint is gone.
But there is still oil based finish, and oil based stain, and oil based primer, among other things.
That's why Rustoleum isn't going away so fast.

As for latex vs oil. The OP was talking about painting over steel. For a solid base coating on the steel, latex is an awful choice. Latex is pretty water permeable, and is a lousy choice for protecting steel from corrosion.
Oil gets brittle, and has issues with wood expanding and contracting, but that's not an issue with steel, and it is a much better water barrier on metal.

Since the base coat is in good shape, either will be fine if you're just looking to improve the color and add some new UV protection to the base coat, but I'd still use oil on this. Oil is just easier to work with too, if you use the right brushes.

 

[LG63]

I found some Behr oil based enamel at Home Depot so after a TSP wash down I plan to apply that directly over the old finish.

 

[theoldwizard1]

I don't mean to offend anyone on this thread but applying latex over oil primer (or finish coat) is fine and totally acceptable. If the base-coat is an oil finish coat then you would want to prep the surface first. TSP and a good scuffing with a green 3M scotch type pad are fine for this step. I would then apply a quality latex top coat and be done.

+1 !

I worked my way through college selling millions of gallons of paint (okay, only thousands) at Sears almost 40 years ago. The prep process has not changed.

The Scotch pad is only necessary if the old paint has any gloss. If it does, scuff first and then wash with TSP if you can find it. Outlawed in many parts of the country. If you have bare metal (not just a little peek-a-boo) get a metal primer.


PS I haven't bought Sear paint in many, many years. I like Behr, except Behr ceiling paint.

 

[LG63]

I washed down with TSP today and based on the brown runoff I saw it must have done a pretty effective job of cutting through the oxidized layer. I think I've got a good sound surface ready for the new paint. Thanks for all the replies.

 

[Tim The Tool Man]

...The Scotch pad is only necessary if the old paint has any gloss. If it does, scuff first and then wash with TSP if you can find it. Outlawed in many parts of the country. If you have bare metal (not just a little peek-a-boo) get a metal primer...

You can still find TSP in those areas where is is no longer sold in stores, most boxes of dish washing detergent found at any grocery store contain enough TSP to get the job done. Just avoid the "phosphate free" ones.