Spot Paint Maintenance, Repaints over old oil based paint
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BobSorensen



Joined: 10 Jan 2010
Posts: 1

PostPosted: Sun Jan 10, 2010 10:44 pm    Post subject: Spot Paint Maintenance, Repaints over old oil based paint Reply with quote

John: Enjoyed your recent article in Painting and Wallcovering Contractor magazine. I am especially interested in what you had to say about a spot maintenance approach to older homes' exteriors. In the Seattle area the oldest homes generally are from the early 1900's. Often the underlying paints still appear to be intact but often "lift" when topcoated. Bubbles sometimes occur in a matter of hours as the acrylic dries and contracts. In your article you mention success using a weak oil based primer and topcoat in your spot maintenance approach. Which products do you or other painters prefer? I would like a recommendation for a weak oil based primer. I know what you are getting at here, you don't want to use something with a tenacious "bite" as that might backfire and lift off the old paint. I assume you are using a 100% acrylic topcoat? I have had success in these cases using less expensive lines of paint, what are sometimes referred to contractor grade. I've used Kelly Moore and Sherwin Williams with good luck. Others out there have some suggestions for how to approach these jobs? Bob Sorensen
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johnleeke
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Joined: 20 Aug 2004
Posts: 2940
Location: Portland, Maine, USA

PostPosted: Mon Jan 11, 2010 11:31 am    Post subject: Reply with quote

Practically any primer and top coat works well with Spot Paint Maintenance. The success of this method depends on the procedure and on the skills and knowledge of the painter. Success does not depend on the materials used, which is why we developed the method since the paint companies keep going out of business or changing their products. Simply use your best judgment when selecting specific paint products.

We often use an oil-based linseed oil or alkyd resin primer with 100% acrylic topcoats. Oil-based alkyd top coats work too, as well as traditional linseed oil paints.

Actually you do want a primer that penetrates well into the bare wood of the spot. In fact, the method has a separate pre-treatment for best penetration. Since the primer and topcoats are only lapped over onto the surround paint a little (as little as possible) how the primer acts with the surrounding paint is of little consequence.

Download the attachment below, which is a step-by-step paint schedule for Spot Paint Maintenance. This schedule works well for us here in coastal Maine where the weather is brutal to the extreme with both humid hot summers and icy cold winters.



SpotPaintSchd-scr.pdf
 Description:
Spot Paint Maintenance, step-by-step paint schedule.

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 Filename:  SpotPaintSchd-scr.pdf
 Filesize:  105.85 KB
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John

by hammer and hand great works do stand
by pen and thought best words are wrought


Last edited by johnleeke on Wed Aug 08, 2018 2:41 pm; edited 1 time in total
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BenS



Joined: 08 May 2018
Posts: 10
Location: Victoria, British Columbia

PostPosted: Wed Aug 08, 2018 11:30 am    Post subject: Painting over good paint Reply with quote

I wanted to revive this topic as I am not sure I understand the answer (and the link to the magazine article is dead now).

John, are you saying that old, still-functioning, paint should be primed over completely and then painted? Is the delamination that occurs when acrylic is painted over old oil the result of the missing primer coat?

Will the wet abrasive scrub create enough "key" (roughness) on the existing paint for the primer to grab on to? Or should I look at any wet sanding to ensure this.

Since I have only trim, I am not concerned with making the paint too thick for water vapour to permeate. Although I am on the fence about aesthetics of the differing thicknesses of the areas where the paint has been completely removed.
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johnleeke
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Joined: 20 Aug 2004
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Location: Portland, Maine, USA

PostPosted: Wed Aug 08, 2018 3:04 pm    Post subject: Reply with quote

Quote:
John, are you saying that old, still-functioning, paint should be primed over completely and then painted?


No, "spot paint maintenance" is the alternative to priming and topcoating over the whole surface. It is only done in spots.

Quote:
Is the delamination that occurs when acrylic is painted over old oil the result of the missing primer coat?


It could be, but, I never apply acrylic over old oil paint without priming first with an oil-base alkyd resin primer, so I don't know about that delamination.

Quote:
Will the wet abrasive scrub create enough "key" (roughness) on the existing paint for the primer to grab on to? Or should I look at any wet sanding to ensure this.


The wet abrasive scrub may roughen the existing paint somewhat, but it's main purpose is to clean the surface. I depend on the primer to effective adhere the topcoats.
More here on Wet Abrasive Scrub:
http://historichomeworks.com/forum/viewtopic.php?t=1751

Quote:
Since I have only trim, I am not concerned with making the paint too thick for water vapour to permeate.


The thickness/permeability issue applies equally to exterior trim.

Quote:
Although I am on the fence about aesthetics of the differing thicknesses of the areas where the paint has been completely removed.


Do a test section on a less important wall, then stand back and decide if it meets you aesthetic needs.

_________________
John

by hammer and hand great works do stand
by pen and thought best words are wrought
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BenS



Joined: 08 May 2018
Posts: 10
Location: Victoria, British Columbia

PostPosted: Sun Aug 12, 2018 3:02 am    Post subject: Reply with quote

Ok, I think I understand the spot painting vs recovering the whole surface.

To give an idea of how much paint still adhering I have, here at some photos of (1) the underside of a gable (flaked right off or scraped easily) and (2) the trim on a window (adhered well, mostly didn't come off through scraping).

The thickness looks to be about 1/2 the thickness of a dime.

I'm going to attempt priming and then painting over the existing paint unless anyone here tells me it will definitely lead to failure.



Screenshot_20180810-175519.png
 Description:
Underside of gable showing soffit where paint came off easily.
 Filesize:  2.67 MB
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Screenshot_20180810-175519.png



Screenshot_20180810-175442.png
 Description:
Trim on main floor window where paint was relatively intact.
 Filesize:  1.47 MB
 Viewed:  19 Time(s)

Screenshot_20180810-175442.png


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