50 degrees seems to be the magic number for temp. I have only used the perlite from WalMart. Big size small bag. There are other sizes too, the perlite helps with the weight. I like the look I get with the larger size but plan on getting some of the finer stuff soon. Try your local Nursery. I got a huge bag of Vermiculite from them, gives it a sparkly/brown tone to the piece.
Paws

Perlite does come in large(4 ft tall )bags.Best place is a cement specialty place,or masonry.I don't buy from hardware stores of any sort.
I looked around and found a number of suppliers of cement,colourant,sands,plasticizers,silica and perlite and other components.HD did not have anything but grey cement and admix,in any volume.If you have the opportunity,search out specialty sources.Find them thru web searches,or talk to others on this site in your area.What I have here wouldn't for the most part be good for you.
As to perlite sizes-It comes in several sizes and grades.Generally,you want industrial grade and the size is up to you.I use a very fine grind(called cryogenic by my supplier,WR Grace)which won't be good for structural pieces.Go for a larger size here.In this case only,size DOES matter!
Cheers from Canada's West Coast

Hi Scbnymph
Your garage will be fine if you make a curing box.
A big ole box, big enough for your tufa and a light blub.
Be careful with bulb placement if box is flamable.

OR cheaper and better find yourself a FREE little chest freezer that is broken and use that and your light bulb to cure your tufa. The beauty of a small freezer is the top makes a great water proof work bench.:)
The light bulb will keep your tufa nice and toasty.
Wrap your tufa tightly in a plastic bag to keep it damp without steaming up you light bulb. High humidity in the box could be a little shocking.:)

Check your local phonebook for Building Materials or Masonry Supplies. The commercial places will often sell to retail buyers.

While 50°F works fine, the professionals seem to think that anything above freezing is do-able. There is some heat usually generated in the curing process. But since I work mostly by hand, I usually find the 32-40°F range too uncomfortable. Just keep in mind that while you can WORK at 40°, the temps may drop lower while the piece is curing and cause problems. This has happened on a 50° day, and I found that the nightime temps were expected to drop suddenly to below freezing. So I covered the project with plastic sheeting, then a blanket, and had no negative results.

Although you didn't ask, the other end of the temp question is 90°F max. In this I DO have experience!

Sue

Well Guys.....

Thank you all for your advice and suggestions. I am fairly lucky in that my local Lowes & HD sell the 50lb bags of grey Portland Cement made by Quickrete so no problems there. I may search out a better supplier if I really get into this but this will do initially

As for the perlite I will take another look in Walmart, Lowe's & HD for larger bags otherwise I will have to start visiting all the local building suppliers (and there are a lot of them!). Would Lowe's / HD have Perlite in their building supply sections??

Oh, one more question - What exactly is "vermiculate"??

Thanks Again

The Home Depot near me has perlite in the garden section inside the store with the specialty soils like cactus mix, small bags of river stones and such. Tho only size they carry is $2.99 for about 8 quarts. They don't carry vermiculite.

Vermiculite is used in potting soil like perlite to help airiate(sp) the soil. It is fine and looks brown/copper and sparkles in the right light. Just add like you would the perlite.
Paws