I cannot think of a single topic in the paint department that is fraught with more misinformation and mythology than that of paint touch up. I will attempt to shed some light on this subject. First of all we must start from the premise that there really is no such thing as perfectly touching up any painted surface. Unfortunately the paint industry has done everything possible to create and fuel this myth. Why would anyone consistently and repeatedly misrepresent (I call it lying) this very important aspect of their product? Quite simply it is because this is what we want to be told. Yes, sometimes we want to be lied to! Afterall who really wants to be told that the entire wall is going to have to be repainted after the electrician carelessly gets his dirty hands all over the freshly painted walls of your remodel? So you see we are all complicit in the big lie or myth of paint touch up.
Let’s look at this scientifically for a moment. If you are applying one mil thickness of paint over just a portion of another layer of paint, physics tells us that the light reflecting off this surface is going to reveal the difference between the two. This results in a spot that telegraphs itself, especially when viewed from an angle. So there is in fact no sound scientific basis to support the notion of flawless touch up.
Despite the above paragraph, I can’t tell you the number of times I hear the complaint from painters and homeowners alike, “This paint didn’t touch up, and when I use XYZ brand I never have that problem.” What exactly is going on here? Well quite simply sometimes you do “get away” with touching paint up. In other words, in this situation, under these lighting conditions, with this sheen of paint, with this particular color, nobody can notice (easily) that you have touched it up. Yet the fact remains that you can tell the difference if you look closely.
The lower the sheen of paint, the less likely that you will see a given touch up. This is because flat paint scatters light in every direction. In essence it is just confusing your eyes so that you don’t see what is going on. High gloss paint reflects light primarily in one direction (back at you), therefore it more readily shows the touch up. The surface and air temperatures at the time of the original painting, and at the time of the touch up attempt also play into the equation. Temperature has a large affect on the coalescing of an acrylic paint film, and subsequently the pigments contained in that film. Therefore when there is a wide discrepancy between temperatures of when the original paint was applied and when the touch up is being attempted, you get an exaggerated difference between the two. This is particularly the case when touching up exterior deep colors.
Another problem that presents itself when attempting the imposible (touching up paint), is that different pigments have differing weights. The result of this is that if the paint is not thoroughly mixed either when it was originally applied, or when it is used as touch up, you will potentially get quite a different color. I find this is the one that confuses people the most. I often ear, “I used the same paint from the same can, how can it look so different?” This is emphasized when using darker colors as they have more color pigments added to them. Application technique also adds to the complexity of the situation. A wall that was originally painted with a roller or by spray, certainly cannot be touched up with a brush; yet this is what all too often is attempted.
One of the most common problem that occurs however is one that can easily be avoided. Many times a large 5 gallon container is purchased to do a job and then the customer comes back later to buy a quart of the same paint for touch up. Yet another inescapable fact in the world of paint is that no two cans are EXACTLY the same. Once again we bump our heads against the immutable laws of physics and chemisty. The most reasonable thing to do is to take a small amount of the paint from the 5 gallon container BEFORE we start painting, and reserve it for touch up later. This small step is ignored at your peril. You know the old adage, “an ounce of prevention…”
One last thing that affects touch up is the quality of the paint itself. Interstingly; the cheaper the paint the better the chances are that you won’t notice the touch up. Higher quality paints have more expensive pigments and resins which can build up sheen especially in the flat/matte range. So sometimes the more expensive a can of paint is the harder it is to touch up.
So you see (whew!) this is really not such a simple thing. A paint film is a very complex thing and as such should be treated with the respect and dignity that you would normally reserve for the granite countertop or the newly laid carpeting. We expect a lot from out painted walls and sometimes they just need a little love. I hope this helps.
