What is a good elastomeric paint product to use over SIPs?
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Any recommendations or experience shared would be welcome!
I am about to start construction on a home built with SIPs. I was going to use Grailcoat but have seen here that people have had trouble with cracking and water damage to the OSB skin. My builder thinks you always need some kind of gap to allow moisture to move between the OSB and the exterior. I would like a “stucco look” and am looking at elastomeric paints with sand added to one coat or grailcoat like product.
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What substrate are you planning to paint on? Surely not the SIPS themselves. The outer OSB face of the SIPS is a sheathing layer not a cladding layer. Over your SIPS you'll need first a WRB then a cladding and ideally a furred out air space between them.
Grailcoat said they would "guarantee" 20 years SIPS with grailcoat directly applied (sealer and then 2 layers of grailcoat).
I see now it will take more. Start with Tyvek or do you recommend one of the new and improved WRB like HardieWrap? Then would you recommend Hardie board or cement board followed by caulking the gaps with elastomeric caulk and then painting with elastomeric paint with sand in one layer to get the stucco look? Would that work?
If it gets too expensive I'll have to look at vinyl siding but I'd rather not.
Thanks for your advice.
I would recommend this blog by Martin Holladay about correct use of WRBs-
https://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-water-resistive-barriers
I don't have any direct experience with elastomeric paints. I do know a reputable contractor who did one coat of stucco over his old wood lap siding and finished the stucco with elastomeric paint and it has lasted for several years with no signs of degradation.
In this case the elastomeric coating was in order to cut down on costs. Only the one coat of stucco was needed instead of the traditional 3 coat stucco application. Can you use elastomeric paint with a non-stucco cladding and still get a stucco look? I don't know.
I believe the coatings of EIFS systems are similar elastomeric coatings but it would not be recommendable (or cheap) to add a EIFS system outboard your SIPS.
If you are in a cold climate I would worry more about ensure an air tight SIPS execution and then very good water management details. Of the sheathing materials OSB is the most susceptible to moisture problems so choose and detail your cladding wisely.
I would do every thing possible to protect the SIP. The interior and exterior OSB skins along with the foam core form the structure of the house. The OSB does not tolerate water well at all. A little water will turn the OSB to oatmeal.
If you want to know what you have in store do a little research on EIFS. Know the construction is not the same but it is similar enough. Improperly installed EIFS allowed water in and did not provide a method for the walls to dry. The OSB rotted. The mositure caused mold problems as well due to the difference in construction. In the case of SIPs you may not get the mold but you will weaken the structure.
In addition to the above article I would go to the building science website and research the article on "mind the gap:"
Thank you! I appreciate your help.