Thoughts on "EL-Cheapo" LP flattener?

I have finally come up with a really nice looking,and really cheap idea for a workable LP flattener.I have employed it just yesterday,but haven't used it yet.Will start it next week,and follow up here.I felt some of you guys might save some money(for new music) should this work as I expect. What I did was to get two 12"x12" slabs of sandstone/marble,which have a nice weight to them,but not too heavy.Also,they can be purchased locally(like a flooring tile,about half inch thick)and can be had in many colors,so you can match to room decor.
I have been thinking about this for awhile, and decided against something "hard" pressing the LP,because I feel it would damage the grooves,to an extent,and I'm not happy about splurging for a pricey flattener,from a mainstream mfgr,since this year I have spent quite a bit of money on the hobby already.
So,what I did was get some very thin cork liner(easily bought from a Home Depot type store)which has one side as an adhesive.....The adhesive side is stuck to one side of the marble slab/tile(cut to perfect 12"x12" fit).You want to do this to "both" pieces!You can even place some soft felt to the bottom of one of the plates/tiles if you want to keep it on a shelf.
Now just place an LP between both slabs,and place it in a windowsill,not directly in sunlight,but enough exposure to get slightly warm.Leave this in place for a few days(I still must experiment with "time" exposure here)and I see no reason(I hope) for this not to work.The cork will not put damaging pressure on the grooves,since there is a softness to it,but it is SO thin,that the pressure of both slabs(about half inch thick,btw)should do the trick.
Here,pay close attention to temperatures on the windowsill,and maybe it is best to be very wary of what season of the year gives best results.As sunlight can get hot.REMEMBER to keep a "shade" down and not have direct exposure to sun.We just want general warmth,over a couple of days.With this,and the weight of the slabs I pretty much feel it will work,but it is a cheap/cute effort,so worthwhile.Some of you may have better ways of getting it to be more effective,and I am all ears!
I have a good hunch this should work,but some experimentation will be necessary.In my room,it looks quite nice,as it matches my room decor,and takes up very little space.

All in all,this cost me a total of 8 dollars!
A comment, try using a light bulb as the warming source. It will be easier to adjust the temp, keep it exact, keep it controllable.
Put the slabs, and light source in a box, add/close vents to make it perfect.
(also, MUCH easier to use two sheets of 1/4" thick glass for the flatteners, the stone may just be too heavy, and it may damage the LP.
Over the Christmas holidays, I had bought a couple of new (sealed) LPs in Omaha, Nebraska only to find out (once I got back to Texas) the vinyl looked like it was stored next to a space heater. I got tired of calling back to the record store trying to connect to "the right manager" to get them replaced, so I took matters into my own hands (er...oven).

Following the ground-breaking work of others in the 'asylum, I ran out to Home Depot and bought (2) highly polished 12" square marble tiles (for a whopping $3.48 each). I scrubbed the tiles to remove any dust and dried them completely. Then, I went searching for the most warped LP I could find - Silversun Pickups "Carnavas".

I gave the LP a good manual scrubbing with DiscDoc products, and vacuumed it dry with my $1.76 vinyl vac tool (see other thread in the Vinyl Asylum). After pre-heating my oven to 175 degrees, I sandwiched the LP between the 2 marble tiles, and baked it for 25 minutes @ 175 degrees. After 25 minutes, I turned off the oven and opened the door until cool.

Results? The LP is now flat as an accountant's ass (my apologies to any accountants I have offended). Actually, I'm quite amazed.

My questions are:

1) Has anyone else tried this method?
2) Is 25 minutes @ 175 degrees the optimal time / temperature?

Any other suggestions? If you have a warped (but otherwise pristine LP) you owe it to yourself to try this.

Subsequently, I've learned that this works better with thicker LPs. I tried this with a *very* mangled Traveling Wilbury's LP (that is paper-thin) and the results weren't as significant.
Nick- your technique is similar to what I've heard over the years. 175 degrees for 30-45 minutes. plate glass will work fine, as well and perhaps easier to keep clean. Next time try leaving the oven door closed and let it gradually cool over a couple of hours.
It's worked for me, but careful with the heat. I've ruined records trying to get it right. Thicker and heavier is better. I would experiment with shorter active heating time / longer cool down time with door closed.
Also, convection ovens are safer, and if your oven does 150 degrees, even safer.
Dear Sirspeedy: I assume you still have the Sota TT that has a vacuum hold down record, right?, then why do you need an additional method to Lp flattener ?.

Regards and enjoy the music.
Raul,there do happen to be some lp's that cannot be flattened with "any" vacuum system.If a disc is too dished,the "lip" on the platter cannot grip the disc,for a good seal.
Also,many collectible LP's are priced much lower,if somewhat dished.So owning a workable flattener is a good thing as I see it.
I believe "dishing" cannot be fixed by a commercial flatener. My friend has an Air tight flatener and it seems that it cannot fix dishing problems. Have tried it a couple times especially on those paper thin vinyl.
Your idea is worth trying. The slabs should be super clean. I don't think it's necessary to worry about the weight of the slab - the stylus pressure in the groove is appx. 50,000 lbs/sq.inch, and a few pounds of slabs will not crush the groove lands.
Sirspeedy, I thought the reflex clamp would help flatten the dish enough for the vacuum to grab it ? I have clamped out any dish I have seen so far on my VPI for the most part. Are we talking dished or bowled here ? I just trying to get a perspective on when I could use your flattening method. I have heard some pretty amazing things about the Sota platters and vacuum.
OK,I added a very thin layer of "self adhesive" aluminum foil liner,over the pliant layer of self adhesive cork.This holds the LP in place quite well,and does not stress the grooves at all.
Result,after four days in the "El-Cheapo" LP press....a "dished" LP of "Out of The Cool"(original pressing,and not cheap)was "dead flat"!
Total cost with all modifications was 16 dollars!BTW,I addad five felt pads to the bottom and the device which now has a real classy look to it,and it works!
Sorry if I was not clear.The SOTA Cosmos,and clamp/vacuum system is a fabulous and effective product.I absolutely love this table!!Actually a real giant killer,in sonics and performance!!.....
However there are some lp's that rise above the "lip" and don't allow a vacuum seal.In my almost 2500 lp collection,I don't think I have more than twenty,but I do see some collectible lp's that are lowered in price,when this is evident...hence my desire for the flattener.Which looks way cool,and works!

Give us the final specs so I can go to Home Depot and buy the materials! Great idea and good thinking!
Dmgrant1,all you need to know,is already posted here.
Best of luck.
Thank you Sir, and I will comb through the post. Again thanks for sharing your idea.