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Question DetailsAsked on 7/9/2016

I have a painted concrete basement floor do I have to remove all paint before repainting?

Painted concrete basement floor, previously had a water leak causing the paint around the brick walls to chip and flake. The paint in the middle of the room is not chipping or flaking, but looks worn from use. I was hoping to scrape up the paint around the brick walls and then paint it and repaint the middle of the floor with the same color. I made the assumption that I would have to sand and prep the old paint, but I have been told I have to REMOVE all the old paint. Is this true?

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NOTE - if the outer paint flaked and chipped due to water under it (moisture wicking up through the concrete), leaving the existing paint in the center of the floor risks the same thing happening there, either in a wet season due to water table rising, or because once you paint the entire floor it will lock in the moisture that is escaping now so possible it willthen happen at the center of the floor too, depending on whether the moisture is coming from the foundation walls only or also up from below the slab. So consider that risk versus the amount of effort to remove the paint chemically (easier) or with a belt sander.

As long as you use a compatible paint, generally if you clean it well and sand/chip off any loose paint, and sand the edges of the painted areas to provide a smooth transition, you can get a suitable paintjob - not perfect looking but acceptable for a normal knock-about basement.

If oil paint or is a glossy finish needs to be touch sanded to provide "tooth" for the next coat - best to do this with any type of paint, actually - I normally use 120 grit sandpaper for this, and of course excellent TSP cleaning and complete drying day before painting. If oil based now then can generally use oil (mineral spirits) or acrylix latex or latex or latex enamel over it, if latex or acrylic only latex or acrylic latex and some enamels - thogh some enamels can only go over oil or enamel paints successfully because some have oil or mineral-spirits (paint thinner) based solvents. If a urea or epoxy now generally takes major sanding to roughen and dull the surface or another coat will not stick, and may or may not be able to use oil based over it based depending on composition.

(BTW - oil based is generally a LOT (maybe 2-4 times) more traffic resistant than latexes, epoxy probably about another 2-4 times more durable, and polyurea finishes (pro application only basically) maybe 50-100% more durable than that).

Of course, test a small spot first for blistering/bubbling/peeling and for adhesion on the existing paint after curing before doing the entire thing. For normal appearance and wearability (I get about 12-15 years in my garage before I get wear-through) I like the Sears (Sherwin Williams make, at my last check) Concrete and Garage Floor latex enamel if you are not going for a higher-end oil or epoxy finish.

Answered 3 years ago by LCD

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