Matching Existing Knockdown Texture
One of the biggest challenges of working with knockdown texture is trying to match an existing texture. Drywall repairs are inevitable and once the repair is floated out, you have to try and match the existing texture so it doesn't look like a patch. Whether the repair is a result of drywall cracking, screw pops, holes, knicks and scratches, corner bead blowout or anything else, matching knockdown texture is the most difficult part of the repair. As explained below, the best way to effectively match knockdown texture is actually not to knock it down at all.
Key to a good Knockdown Texture
To do a good knockdown drywall texture you have to be able to reliably estimate the moment when the mud has set just enough but not too much before knocking it down. If the mud has not set enough, it will smear easily, causing the small blobs to smooth out into a large thin island. If the mud has set to much before knocking it down, it will tend to chunk-up and may even leave scratches and dried clumps of mud that drag through the leftover blobs. Scratches and tool marks in a knockdown texture are nearly impossible to fix so it is best to avoid them in the first place.
The problem with knockdown texture on drywall patches
The main problem with spraying knockdown texture on a patch is that the area surrounding the repair is usually painted. When texturing a repair, you have to spray at least some texture lightly over part of the surrounding painted section in order to blend the new texture with the old.
Blobs of texture sprayed over top of the painted portion will set up much slower than those sprayed directly over the patch. Finish coat mud on the repair has a tendency to suck moisture out of the texture and hasten it's dry time.
Because of this problem, when you are trying to find the perfect time to knock down your texture you are faced with the following dilema. If you try to knockdown the texure when the patch section is ready, the texture on the existing paint will be too wet and will simply smear out into an indistinguishable mess. On the other hand, if you wait until the area over the painted section is ready, the texture on the patch will be too dry.
How to solve this problem
In order to solve this problem, it is actually best when doing drywall repair to let sprayed texture dry in place without knocking it down. When spraying knockdown texture over a patch, it is better to focus on the size and distribution of the blobs and not to worry about knocking it down until it is completely dry. This way, you avoid the problem of one section being knocked down too much and another section not being knocked down enough.
Once the texture dries, you can take a simple sanding spounge and lightly sand the texture to blend it into the existing texture. In essence, doing it this way turns it into a sand-down texture rather than a knock-down texture.
Can you sand down all textures?
This leads to an interresting thought about knockdown textures in general. Knockdown drywall textures are basically created by taking a heavy, dynamic texture and softening it by lowering it's profile. The challenge when doing any kind of knockdown texure, whether it is spray knockdown, crows-foot stomp knockdown, rosebud knockdown, or any other knockdown is determining the perfect moment to hit it with the knife and knock it down
If you wanted to, you could actually get away with leaving any of these textures to dry in place and simply sand them down once dry. You may of course cringe at the idea of sanding down an entire house rather than using a knockdown knife when texturing. However, sanding down texture is fairly easy and goes pretty quickly. One advantage to sanding down your texture is that you have some control over the final result. You can choose to sand a little extra in some areas and less in others. This way you can correct uneven spots in the application and possibly even acheive a more uniform looking knockdown texture
Whether you choose to sand down large texture jobs or not, you will likely agree that using this technique on drywall repairs leads to a better looking knockdown texture repair.