Do I need to sand oil paint before priming for latex?

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  #1  
Old 08-31-09, 07:20 AM
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Do I need to sand oil paint before priming for latex?

I guess the safest thing would be to sand the oil-painted trim before I primed with latex primer, but I see some primers out there that say they will stick to anything without priming.

Thoughts?
 
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Old 08-31-09, 08:46 AM
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If the oil paint is high gloss it certainly wouldn't hurt to scuff sand it.Basically I'd start with whatever the particular product you use's instructions say.Stick to a quality product,either from a well known name brand paint line or a top quality primer maker like Zinsser, not a big box product and if you do sand clean off the residue well.
 
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Old 08-31-09, 10:26 AM
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I'd be leary of using a latex primer over oil base enamel. It would be better to use a solvent based primer. Pigmented shellac like zinnser's BIN is best but good results can be had by using a decent oil base primer.

Scuff sanding is always a good idea. The only way you could skip sanding would be to correctly use a deglosser [it softens the existing paint for a short period of time] I often do both.
 
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Old 09-03-09, 07:41 PM
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Chemical deglossers are not very effective on oil based paints for deglossing.

Sanding always improves adhesion. There are times where you can't or should not sand (if there is lead paint present for instance). In these situations, you can get by without sanding BUT the surface must be squeaky clean.

There are latex primers that will adhere to glossy oil paints. These primers are caled "bonding primers". Most latex primers have very poor adhesion to glossy surfaces, but the bonding primers are effective for this. The best one (in my humble opinion) is XIM's UMA (Urethane Modified Acrylic). But again, you need to know that latex paint is easily repelled by surface contamination. Latex bonding primers are much less forgiving if the surface is not absolutely clean. An oil based bonding primer (Coverstain or XIM 400 white or something similar) is a little more forgiving.

The latex bonding primers are still subject to long cure times, which means that even though they will develop adhesion, they are soft and subject to scratching off for a couple of weeks until they cure. The solvent bonding primers develop adhesion and scratch resistance very quickly.
 
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Old 09-09-09, 01:07 AM
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Slatz's post = Gospel

Slatz said it well...

The BEST prep on oil (assuming no lead!!!) is always sanding.

The "physical profile" generated by sanding is always preferable to the "temporarily tacky" surface of a de-glosser.

After thorough removal of ALL dust, my primer-choices are
1) BIN from Zinsser.
2) C2-One Latex bonding/stainblocker.
3) 123 Latex from Zinsser.

XIM's primer-products are great, but can be hard to find.
If you'r near a FPE retailer, use their Oil primer. Some of the best stuff made...

Faron
 
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