Can I use roundup to kill the grass and weeds, then go back and rake up the ground to lime/fert and seed?

yes you can, a very good way to start a plot if you don't have access to much equipment. Round Up only kills plants that are currently growing so it wont effect your seeds

gmil is right spray the far out of it.

with roundup you can also replant a week later.but dont use any sterilizer or nothing will grow for a while

I hope someone out there has better luck with Roundup than I've had.

I got it to kill weeds and grass before seeding and it said it would "show results within 6 hours."

Well, the "results" were that it just made the grass a little bit brown and didn't kill it at all. This was after I basically soaked the ground with the stuff.

MNow, maybe I have some kind of hardy midwest grass that's super-hard to kill (lol), but I'm looking for something else - Roundup didn't do squat. Just FYI to check and see what works for other people in your neck of the woods before you spend too much money.

Roundup (glyphosate) works very well. Not sure what you were using that promised results in 6 hours, likely highly concentrated name brand stuff. Still, 6 hours seems unreasonable for most plants. I wait a minimum of two weeks before determining what died and what didn't. If high dollar Roundup didn't work at all, something went wrong on your end.

Fast acting roundup formulations add an ingredient to burn plants. This doesn't mean the plants actually die in 6 hours, just that they have been sprayed and they get brown specks (as you observed). Magis is right, patience is still needed for the roundup to actually kill the plant.

When I spray with Glyphosate, (Round Up) I wait at least a week to see real results.

I can see results in 24 hours when I spray. This is on things like johnsongrass, ragweed, pigweed. I'm using generic glyphosate at 2%, adding 1% ammonium sulfate, and adding .5% crop oil spreader/surfactant. Ammonium sulfate is about $20 for a 50lb bag. The spreader is about $50 for a 2.5 gallon jug. I bought generic gly yesterday for $37.50 for a 2.5 gallon jug.

Use AMS & a surfactant.

It was actually Roundup - got it at Home Depot. It just didn't work. Even after a week or more. I didn't really expect the grass to be dead and gone in 6 hours. I just thought the whole "results within 6 hours" claim was a little bit misleading when all it did was turn some of it brown and leave the rest unaffected (seemingly).

I gave in and just dug up the grass in the area (luckily it was small, otherwise I could have had a good workout).

Who knows - maybe I got part of a "weak batch" or something.