Concrete mix question

[fxpose]

I have a near full skid of various bags of dry mortar and stucco mixes which I picked up from Home Depot for almost nothing (torn bags).
I'm currently working on block wall footings and general concrete work for my new patio.
Can I simply add gravel to these mixes and use them as concrete? I realize these premixed stucco and mortars use various ratios of cement and sand. I would like to use them up as part of the concrete mix. I also have bags of plain portland cement which I can add to the mix if need be.

Thanks!

[Tscarborough]

Yes you can do that.

[fxpose]

Thanks Tom. I presume the mix ratio is not that critical. If the mix is looking good in the mixer it's good to go.

[fxpose]

I also have bags of plastic cement. I assume I can also use that (instead of portland cement) mixed with sand and gravel to make standard concrete mix?

[Tscarborough]

Yes, that is fine too.

[fxpose]

Thanks again!
I have another question. I still have several bags of both portland and plastic cements. Would it be cost effective for me to buy 9 cu/ft bags of sand/gravel mix for $30 and use that to make concrete verses buying bags of 90 lb Quikcrete concrete mix @ 3.50 ea?
These are our local Home Depot prices. I assume each 90 lb mix yields not quite 1 cu/ft?

[Tscarborough]

I am sure the concrete mix is 80# bags and that equals .66 cuft. 1 bag of portland cement (94#, 1 cuft) mixed 3-2-1 gravel/sand/cement will equal around 5.6 cuft.

That should enable you to calculate which is more cost effective (Usually buying the aggregate in bulk is where the savings is, but the aggregate in bags is generally not cost effective).