FYI, I wound up adding to the shampoo girl's tip the 20% of what the treatment would normally cost, plus the $5 I usually give. It was not labor intensive, just a spray of deep conditioner, but the salon was pretty busy, so by sitting there these extra few minutes, I was taking up her chair and someone else's seat. Maybe a little overkill but I am not one to haggle over a few bucks if it means paying someone with a thankless job a little extra. I tipped my stylist the normal amount, since he didn't do anything with the extra treatment, but did a fabulous job, as usual.

That treatment is pretty labor intensive, isn't it? I would definitely tip for that. Is this as the shop?

Agree with 12:25.

Find out the standard rate of the kerastase treatment and tip your usual 20% on that.

No one is responding in beauty/fitness, so I'll try here:

I'm getting a haircut today and plan to tip 20% as usual plus a few extra to the washer. But I'm also getting a free kerastase treatment as a special they're offering at my salon today. Do I need to throw in a few extra for that on top of my tip? How much would you recommend?