What is a surface that I can lap on that is around my house?

I need to lap my HSF and I was wondering if there was possibly a surface that I could use...I have mirrors, but how can I be sure that they are perfectly flat?! They look like they are decent quality, but they are hanging on the wall, so I would have to take them off the wall to lap it...I have windows around my house too...any other good surface I could use or the cheapest one I could buy at a store that would still be really good. Thanks!

glass isn't a perfectly flat surface (for example, car windshield leave small spots of water when u have a old/dry wiperblade) but its the closesting thing to flat that you can probably find around your house. Plus, since a block is so small, and the cpu area even smaller, it won't really make much of a difference, lapping it the wrong way will make a greater difference. So basicly, a mirror (2nd surface, glass covered) would work just fine.

Good luck!

so as long as I keep it from bending concave or cenvex, I should be fine using a mirror with the mirror's glass surface on top? If I can do this, then I may lap my HSF tonight and hopefully see better temperatures...I'm really surprised how rough my SLK-900a really is.

if the mirror starts to bend, then you're pressing too hard.
press very lightly, let the weight of the HSF do most of the lapping. It takes a lot longer, but you'll get better results.