The approach is quite tricky and route finding hard, especially during the second day, even with IGM maps. Hiring a local guide of the Cooperative of Guargalla guides is worth it. Their price (by 2005) is 12 $ / day + an additional 60$ for the summit bid. If you also hire a mule, the cost is (by 2005) 10$ / day.
Day one: from Hacienda Guargalla (about 3700m) to Plazapampa (about 3500m), estimated +900m: 8h to 11h (depending on your haulage and trail conditions) over the high paramo into the National Park.
Day two: from Plazapampa (about 3500m) to Yanayacu (3400m) in 0.5h and then to La Playa (about 3600m), estimated +600m , 3.5h to 6h through the cloud forest to the base of the volcano.
From La Playa (about 3600m) start at 2:00 / 02:30 am.
follow the same red lava flow on which is situated La Playa shelter until reaching a flat area above the paramo (vegetation) at about 4000m. The red lava flow flanked by streams is obvious when enough visibility but could be a nightmare to find in a poor one if you have no local guide or haven't identified it the previous day.
The flat area above the paramo is sometimes used by the few commercial expeditions as an alternative to La Playa decreasing the required vertical gain to 1250m. From there continue on the featureless southwest face until reaching the summit plateau at about 5150m.
By spring 2005 there were 3 craters one of which was active. Depending on volcano activity one or more craters may be active. This activity impacts crater shape and height, and thus the location of Sangay summit.
Ascent: average 6h to 7h
Descent: average 2h30 to 3H30
Rain gear is a must. Ecuadorian "Venus" rubber boots (6$ - in 2005) help a lot on the muddy approach and for the frequent river crossings.
Crampons are very useful even when no snow because the imbibed volcanic ash can be hard frozen due to cold and thus quite slippery. A helmet is a must: many things are loose up there and easily roll down the slopes, especially during day time…
Poles are of the highest importance on such terrain when not frozen. They also help a lot during the very muddy approach .
There is a store dedicated to rubber products where one is able to buy rubber boots or plastic ponchos for the market price without having to “negotiate” the price ! In Riobamba, 50m in front the Condamine Market main entrance there is a store called "bota caucho" where the Venus rubber boots are sold for $5 (and that's the price my guide told me) right away, without having to negotiate. They have other choices of rubber boots including some American brands as well as ponchos for $5 to $12 depending on the quality. I bought a $6 one which was good enough for Sangay. The prices are those of May 2005.