Hello,

I hired a painter to paint the inside of my house which had semi-gloss
paint. He covered it with semi-gloss of a different color. I just
learned he did not buff or sand the original coat before he painted
over it. When I confronted him about it, he said this was proper, but
he would come back and re-do the job if a problem arose within the
warranty period.

 I want links to two answers from experts who have answered :
Approximately how long before problems like flaking or peeling appear
after painting semi-gloss over semi-gloss without sanding.

 Be sure to give the qualifications of the experts.

As 'old' paint, it has 'cured' and should have been sanded. The only
situation in which you can successfully paint over any type gloss
paint is when it is overcoated [ gloss over gloss] BEFORE the first
coat is cured. When the surface is dry to the touch but it has not
hardened underneath. I have used this method to achieve a very good
gloss coat on a boat hull, that is subject to weather and salt spray.
And it lasted four years. On a house, much longer. When you lay on the
second coat, it will be a bit 'clingy' on the brush, but this is
overcome by 'painting by squares', and always brushing back to the
done section. always in the one direction. Hope this helps.