O/T Stucco on house in high humidity?

Try checking the manufacturers product data for the material to be used, substrate and reinforcing designs, and see if there are any listed warnings about high humidity. You'll find data for most materials on the internet, usually from a manufacturers web site.

Field applied systems like Dryvit,and others, materials that have elastomeric properties etc, might be of interest, but there are a lot of materials out there, and in service, the manufacturers should be able to confirm whether the product is suited for the climate or not.

Portland based materials are usually strong, in all these systems it would appear that the bond strength is most important, along with reinforcing mesh design, and compressive strengths of the materials, portland based products are good performing materials, when it needs to be strong.

If a material that is permeable, one that can be saturated with moisture, causing delamination, spalling, fracturing, the manufacturer should warn you about it.

I'm really not that knowledgeable about stucco systems, knew the Dryvit systems quite well, kind of similar, mostly used on E.I.F.S. panels, also field applied to cementitious base systems reinforced with panzer mesh. Sounds like you need something that has good bond strength and possibly has a sealed finish to it when done, to keep moisture out, or at least it would seem that way, one thing in your favor is not having a freeze thaw cycle to contend with.

Honestly, i've never seen it happen, then again, i live in the mid atlantic. I assume the deep south would have problems with cracking.

• Synthetic Stucco

I've been on some large E.I.F.S. jobs, heavy commercial type panels constructed of galvanized metal studs with an EIFS system applied to foam, dense glass gypsum board and cementitious board. The panelized systems work, as by design there is a cavity and weep system. The field applied to the sheet goods as mentioned above would be more prone to delamination, but Dryvit was a good product, their primus base coat is polymer based, excellent bond strength, I recall the elastomeric finishes being good, being installed by experienced people helps too.

Portland Cement based materials are usually superior materials, I think you would have to compare ASTM tests and or specifications to see this.

One thing I would never allow on any structural steel buildings I did, and even NY state design and construction disallowed it in there specifications, was gypsum based sprayed on fireproofing used to give the steel frame ratings called for in the drawings and spec's for the job. Portland based fireproofing was much better.

The reason was, that gypsum based fireproofing was too easily compromised, it's a weaker material, it would take a beating before it got covered up and floors finished during construction, too much would get knocked off, weather, all kinds of trades attaching their work to the steel scraping areas off that would cause the surrounding areas to fall off, lots of comeback work, re-applying the material would be necessary to insure the fire ratings of the steel were maintained per UL design.

Portland based products cost more, but hold up better with this fireproofing material and probably most others like stucco. Compressive strength adhesion/bond strength, impact specs would probably be better if it's made with portland cement.

I remember a material supplier attempting to get to me when I was doing state correctional facility work, he wanted to sell that gypsum based material to the general contractors like no tomorrow, just by the fact he got past all the barriers and finally got to me, knowing I approved/rejected materials for these jobs, he gave it the old college try, no deal though, substandard material and it violated the spec's for the job.

• Primus Base