Painting Tips by a Professional

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Testing Old Paint: Is It Oil or Latex?

If you paint over old oil-based paint, your new paint will flake off with just a fingernail. Here is the test and what to do if you have old oil.

Don’t paint latex over old oil-based paint!!

Do this test.

Disaster looms…

Testing Old Paint

To re-paint any old paint, you first must know if that old paint is oil-based paint or not.

Did you ever see paint will flake off with just a fingernail? They did not do this test!

Test: Use either acetone, found in nail polish removers (some do not contain acetone) or in a pinch use rubbing alcohol. *

Gloves are good here.

Drip the solvent onto the paint, or put the solvent on a cloth or paper towel and rub the paint.

Does it get gooey? It is latex.

No goo, oil.

A video of the full test is below.

* Note that alcohol does not dissolve latex as well as acetone. A skilled eye will be able to see some latex coagulating.


1. Painting Oil Over Latex

The easy one. You can paint anything over old latex: just sand any nicks, spot prime any bare wall/wood, then clean it and paint.

You’re the lucky ones.

For a great-looking trim paint have a peak at Ben Moore’s Advance: water-based paint but levels out like oil. A great new technology. Not for beginners though.


2. Painting Latex Over Oil

There are two ways to go: sandpaper or liquid de-glosser.

Sandpaper: Sand like a banshee (scratch every bit to create a bond for new paint). Keep your sandpaper fresh. Most trim sanding can be done with 150 grit or so. This sleeve of sandpaper contains 20 sheets. That’s good for about 40 doors, and kept dry never expires.

Liquid de-glosser: You can use the Mother of all Toxic materials, this de-glosser. This stuff evaporates like water on a red-hot skillet. Nasty. Wear your respirator!!

After all the dust is cleaned, paint away with whatever you like.

Pro painters would always use a high-bonding primer first (see below).

* Note that alcohol does not dissolve latex as well as acetone. A skilled eye will be able to see some latex coagulating.


A Bonding Primer

Don’t be afraid that your sanding or de-glossing the old oil was not enough if you use a great bonding primer. Other primers… meh.

Stix really sticks. Hey, did I just make that up?


Let me know below if you have any questions, I check for them regularly.

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