I appreciate your perspective, I can add some info to clarify why I do things the way I do, which might help
Using a wire brush as a first stage does several things: it takes off the smooth surface which A) makes roughing up with the saw blade much less laborious and B) gets the inside of the holes rough also, which does help algae stay attached inside the holes (where the saw blade can't rough up). Mainly though, it's A
I understand that. Also remember that people use mortar to make DIY rock, they've been doing that for a very long time, and with success. They do soak the rock for about a month after making it.
In my process (which was not really spawned by me, but by @Paul B who did it to one of his screens using the same DIY rock philosophy) I spread the mortar on, then tap it off so that only a very thin layer stays on the screen. I sandwich this inbetween wax paper and damp paper towels for 3 days, spritzing with water daily. This is so that it doesn't dry out, but cures enough to stay attached and still be pliable.
Then I hang the screen in a utility sink filled with water and an agitation pump for 3-5 more days, changing the water a couple times. This is vastly different from mortar in construction, so while I see your concern, I do not share it.
The roughing up is what has always been done to allow algae to stay attached (i.e. so that it will not detach under weight, in a waterfall scrubber). Because the mortar is sacrificial and comes off when you harvest the algae, the screen still needs to be rough so that algae will attach after the mortar is gone. The mortar allows short-term fast adhesion, as it goes away you get long-term adhesion to the screen.
You can do this as well. My personal opinion is that roughing up with a saw blade is better as it provides just a bit more surface area for algae to anchor to. Again, it's not about attaching, it's about staying attached when that algae mat is thick and heavy.
I might do a few things that seem unnecessary up front, but that doesn't mean there is no logical reason for my process. I'm not taking your comments negatively so don't get me wrong. I'm also not trying to argue with you about why you might be right or wrong, etc - just filling in the blanks. I've been building scrubbers for nearly 10 years and helping DIYers troubleshoot during that time as well so I do what I do and make recommendations based on what I've seen working across a broad spectrum of examples. But a fresh perspective never hurts!
All that being said, making screens that maximize all adhesion are a pain in the butt. That's why I'm working on a better way...I've been trying to come up with one for a long time
You're right. Bare plastic canvas is very smooth, even under a microscope. Early on (10 years ago) many people tried to just use unroughed canvas and algae grew, but it didn't stay attached very well when growth got thick and heavy. Roughin up with a hole saw helped tremendously. But, it takes a lot of effort and time.A wire brush is not effective to rough up a surface
Using a wire brush as a first stage does several things: it takes off the smooth surface which A) makes roughing up with the saw blade much less laborious and B) gets the inside of the holes rough also, which does help algae stay attached inside the holes (where the saw blade can't rough up). Mainly though, it's A
Construction type concrete products need minimum 30 days dry cure time
Second issue with mortar is there are many Chemiclean that are leeching during this time
I understand that. Also remember that people use mortar to make DIY rock, they've been doing that for a very long time, and with success. They do soak the rock for about a month after making it.
In my process (which was not really spawned by me, but by @Paul B who did it to one of his screens using the same DIY rock philosophy) I spread the mortar on, then tap it off so that only a very thin layer stays on the screen. I sandwich this inbetween wax paper and damp paper towels for 3 days, spritzing with water daily. This is so that it doesn't dry out, but cures enough to stay attached and still be pliable.
Then I hang the screen in a utility sink filled with water and an agitation pump for 3-5 more days, changing the water a couple times. This is vastly different from mortar in construction, so while I see your concern, I do not share it.
The reason for the hand blading is to get the deeper cuts for the mortar to stick.. this isn’t needed.
The roughing up is what has always been done to allow algae to stay attached (i.e. so that it will not detach under weight, in a waterfall scrubber). Because the mortar is sacrificial and comes off when you harvest the algae, the screen still needs to be rough so that algae will attach after the mortar is gone. The mortar allows short-term fast adhesion, as it goes away you get long-term adhesion to the screen.
I would power sand with 40 or 60 grit and be done.
You can do this as well. My personal opinion is that roughing up with a saw blade is better as it provides just a bit more surface area for algae to anchor to. Again, it's not about attaching, it's about staying attached when that algae mat is thick and heavy.
I might do a few things that seem unnecessary up front, but that doesn't mean there is no logical reason for my process. I'm not taking your comments negatively so don't get me wrong. I'm also not trying to argue with you about why you might be right or wrong, etc - just filling in the blanks. I've been building scrubbers for nearly 10 years and helping DIYers troubleshoot during that time as well so I do what I do and make recommendations based on what I've seen working across a broad spectrum of examples. But a fresh perspective never hurts!
All that being said, making screens that maximize all adhesion are a pain in the butt. That's why I'm working on a better way...I've been trying to come up with one for a long time