Hi Steve, use a plastic container large enough to dip the roller into, use as heavy a nap roller cover as you can get with an extension handle, get the wide 18 inch rollers if the job is large, immerse the roller, take it out and let it drip for a second or two above the container, place the roller onto the floor and gently roll forward until it is obvious that the acid mix is no longer flowing off the roller and flooding the floor easily. Stop and roll back along the same path with some pressure to squeeze out the remaining acid, that way you will get nice fresh acid on the floor at both ends.
Do not go too fast and flick an acid rooster tail up in the air, keep a medium speed and do not go too far with each run because you do not want to run the roller dry.
That method is ten times faster than a watering can and applies a relatively even amount of acid onto the floor and puts fresh acid onto the floor. If you pour and spread, the initial pour will be fresh acid, but as you move it across the floor it is being neutralised by the concrete and gets weaker which will give an uneven etch.
The above method is not perfectly even, you will get flooding trails, but it is better than any other method I have tried including a trolley with a big drum of acid and a spray bar at the rear which needed a broom behind it to spread the acid more evenly. I used to do large floors and used a "lawnmower" style water blast head with vacuum pick up to blast and clean off the residue afterwards.
