Fast setting mortars v ordinary stuff

I usually build drystone structures, no mortar is used. Recently I did some small repairs to stonework using the remains of a bag of fast setting cement, usually used for fixing fenceposts. It sets in 5 to 10 minutes.
Obviously this cement can only be prepared in small quantities because it sets too fast but how does it compare to properly prepared ordinary mortars as far as strength and durability goes?
If I add some of this quick setting stuff to ordinary cement does it speed up the set?
Replies
A good example of poor mortar bonding is all these block and brick caps on masonry walls that fall off.
Old craftsmen use to soak bricks in water. This lack of presoaking of masonry units sucks water out too quickly and reduces bonding. Look at the mortar on most walls and they have hairline cracks, cause by too much moisture being sucked out.
This is in responce to mortar bonding strength, not which types.
Edited 10/22/2006 10:39 pm ET by Sungod
???
Sorry but I don't see how your post addresses the issues posed by the OP.
It is important to let mortars cure slowly so that they don't dry out too quickly and cause cracking or failure before the full chemical reaction has been completed but my query is about the long term viability of fast setting mortars. Do the mortars which set in 10 minutes (because they have additives) last as long as mortars of the more conventional types. I am thinking that there must be a payoff for the fast set advantage - is there a weaker bond, does the mortar break down easier when subjected to frost or heat?
NICK
I haven't done what you're saying, but I just want to make sure you keep that cement away from the joints. I.e., point with a softer mortar, so the expansion/contraction of the mortar doesn't break off the stone on either side of the joint.
I imagine it would work ok for setting though.
zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
>> usually used for fixing fenceposts. <<
Are we talking cement, mortar, or concrete?
I may be confusing things by interchanging the words cement and mortar. the stuff I was using is 'Postcrete', can be found on http://www.lafargecement.co.uk
NICK
Re my q: 'Are we talking cement, mortar, or concrete?'
after reading the description at the web link you provided, I'd say it is none of the above, but if anything closer to mortar or maybe even hydraulic cement. Anyway, the product is not indicative of what would be considered a "normal" residential building material.
Therefore the answers to your Qs are probably anyone's best guess...
Personally, my guess would be that the material is not very strong, based on the instructions to fill the hole 1/3 full of water and then add the powder, then sprinkle water on top... For example, in the case of concrete, as with most cements based material, the idea is to get to if fully wetted, but add no more water than is necessary to achieve that, and have it somewhat workable. "Mixing" something in a hole, per the "Postcrete's" instructions if never going to give a uniform mix.
Further, I'd venture a guess that the target consumer group for this product are non-professionals.