I remember your thread about replacing the siding, but don't remember if you mentioned painting the bottom edge and a bit of the back before installing. Jon
T-11 siding is IMHO - horrible product depending on your climate. I do not even like the primer most manufacturers use, cheap cheap. Since you already have the siding, my personal recommendation would be to prime and paint with the best products you can afford, taking extra care on the bottom edges and seams. Also, look into a drip edge / flashing for the bottom and possibly between sheets. I have not used the product in many many years after having to cut 3' off the bottom because it rotted. It lasted about 5-7 years and the worst part was from the outside it looked ok until one day I noticed a small spot that looked bad. Probing around I discovered it was all rot. Also noticed in places with a lot of Sun (Texas) small vertical splits were developing.
I have multiple buildings with T1-11. They were originally painted with the translucent stain and that didn't last at all. I repainted with Behr solid stain with a 20-year warranty. So far so good many years later. It goes on like paint but is still a stain. Behr stain comes in different grades. Also, I always have done two coats. One doesn't do it.
I built a shed with T-11 maybe 18 years ago and stained it. I think I put on 2 coats. Yes, it's faded a bit on the side that gets a lot of sun exposure, but not so badly I feel the need to re-do it. Not sure if paint would have stood up that well.
Agree on multiple coats.
I owned a millwork manufacturing business and had many conversations about coating durability with chemists at large paint manufacturers. You want to use 100% acrylic paint. Sherwin Williams Duration is a good choice, though not cheap. Acrylic paints will have inherent physical flexibility and will move (stretch and contract) with the expansion and contraction of the surface, both thermal expansion and contraction and expansion and contraction caused by humidity changes. The opacity of pigments has a direct relationship with coating durability. The more transparent, the more UV penetrates and degrades the finish (and the material to which the finish is bonded). So, for maximum durability, you want an opaque finish with elasticity. The higher the acrylic content, the more elasticity and the better the bond between the coating and coated surface. And we're talking water cleanup here. Solvent-based paints and stains are more brittle, less elastic, and not as durable, particularly in an exterior environment.
Stain for sure. I have enough paint to scrape on the old farm house and two garages. I built my wood shed in 2004 and put on Cabot "The Finish" white stain. It went on and looked like paint. 18 years later and it still looks pretty good, but I am going to have to do something with the north side that gets all the weather. This was over roughsawn pine that was planed on the outside before staining.
If the bottom of the T-111 is within 8" of the ground, try to make is shorter. If not, water will wick up the wood and cause rot. Been there, done that. A good stain probably provides the best protection.
We have had great results w/ Duration paint at Sherwin Williams