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[Gene GeRue <genegerue AT ruralize.com>]

> Did you apply any type of sealer to the finish coat? I realize that you put
> 30# felt over the plywood, but any concrete/mortar product that I know of
> will allow some moisture to pass. Seems hairline cracks may develop as 
> well due to curing shrinkage and temperature differentials, allowing for
> freeze/thaw damage. I'm not criticizing, just asking questions.

I didn't use a sealer because sealers must be replenished and I design to 
avoid maintenance. Ferrocement cracks are minimized by the myriad wires of 
the mesh. Multiple coats fill voids below; if this one ever shows a problem 
I will put on another layer.

The roof has quite a steep slope. The angle was chosen to match the angle 
of December sun at latitude 36.75N for greenhouse purposes. Full shade 
during summer months. The roof has a one-inch ventilation channel just 
under the plywood, and I guess if I ever have the question I might shine a 
flashlight up there to look for moisture. I would be surprised to see any. 
Protected roofing paper sheds water well. A roofer here in Phoenix told me 
that tile roofs shed about half of rain via the tiles and the rest via the 
paper. The only real concern I have is the many penetrations of the roofing 
paper by all the staples. I believe the impregnated tar in the heavy paper 
will seal the penetrations, but that is only a calculated guess; I am 
ignorant of the fact.

> Personally, I think metal roofing is hard to beat for durability and ease of
> installation.

I agree. I became enamored of standing-seam terne roofs decades ago and 
always thought my ultimate home would have that or slate. Both too 
expensive for who I have become. My ferrocement roof was labor intensive. I 
lifted all the mortar in buckets. On a large roof I would buy or rent a 
pump to put the mortar up there.

Metal roofs need near-perfect installation or they are subject to lifting 
in high winds. Use screws, not nails. They dent and they are dangerous to 
walk on. I believe they are less fire resistant than ferrocement. All that 
said, I may well use metal on the new house.