As luck, or Instagram algorithms, would have it, I found this on my feed - https://www.instagram.com/p/CQfwtuUsuG9/
As the add says; "Simply apply SEMCO Liquid Membrane on wood, concrete, Tiles, Stone or Cladding. Not only does it waterproof but also acts as a crack prevention membrane." I'm wondering if anyone has experience with this product? https://www.semcoworks.com/products/liquid-membrane
"I have this feeling of walking around for days with the wind knocked out of me." - Jim Harrison
I'd have to check the MSDS sheet to see what kind of product it is; but I can't even find it on their site. I'm not specifically familiar with it. But I have tested and sold all kinds of vinyl or acrylic deck coatings and alleged waterproofings, including the siliconized versions, and known some of their chemists. Several were pioneered in this area. I don't want to rush to judgement in this case, but as a class I wouldn't trust them for long-term use in a darkroom sink. They also tend to badly stain. But real-deal true rubber liquid coatings are so fume nasty that most are now illegal to use in this country, and have been replaced by heat-welded hypalon or EDPM etc roll sheet versions, which a specialty roofer could do for you, albeit pricey, for sure. I've even sold liquid hypalon coatings for high-concentration industrial acid vats and aircraft carrier decks. Remarkable stuff, if you don't mind sacrificing your lungs applying it. I'm also familiar with A&B extremely durable urethan-based flexible coatings, equally nasty and now prohibited domestically.
Roll-on acrylics alleviated most of the health hazards and clean-up nightmares, but also tended to embrittle and crack over time, and needed a recoating every couple years. I sure wouldn't want to rely on any of them as a waterproofer without a serious underlying primer, especially from a company like the one under question here, which gives zero real technical info, or even a convenient MSDS link. It appears to me to be just another homeowner bandaid product, and not anything serious. Typically, with those kinds of things, I did board tests and left them out to weather; many failed within weeks or months. If I sound skeptical, it's because that whole category of products comes with an especially high Marketing BS Coefficient. But one can and should always do their own advance testing before relying on any unknown.
Marine epoxy and be done with it forever - just sayin'!
After much thought and research on this issue, I'm going with the West System marine adhesive and epoxy for my sink. It takes longer, is more labor intensive, and requires more time (i.e. 7+ days) to cure. Hopefully, the sink will have "out-gassed" during the 7+ days of curing time. I have confidence this will be a longer lasting waterproof finish than other less costly and quicker alternatives.
Originally Posted by Drew Wiley
"I have this feeling of walking around for days with the wind knocked out of me." - Jim Harrison
Epoxies outgas rather quickly based on their cure time. I have more experience with Smith products. The Smith and West plants are both along the freeway about four miles apart. We sold more Smith epoxy than the in-plant store itself; and it was well known for darkroom sink use, though that was just a tiny application compared to marine and restoration usages. Smith was an eccentric who belonged to an infamous cult demanding a huge percent of his income or else ... so he finally bankrupted and sold his plant to his competitor, West Systems, and West now sell both products parallel, each under its own original name; but these are otherwise quite similar except for optional fillers.
In warm dry weather, the penetrating epoxy sealant takes about 3 days to cure. But only after a day or two you can apply a 2-part epoxy putty fillet to all the sink corners if you want. That is a lot more expensive and time consuming than the penetrating liquid itself. It can be sanded smooth when fully cured itself (likewise, a few days), or be avoided just by using something like Sikaflex urethane caulk on the joints instead (much easier to do). The key is too have all you sink pieces very securely glued and screwed together so that potential gaps in the joints won't be likely to occur anyway.
Applying liquid epoxy : rubber gloves, disposable natural fiber brushes, chemical-resistant mixing pot, long sleeved shirt you don't care about, eye protection, organic-vapor respirator with charcoal filters, and excellent ventilation. Any accidental spills or drops can be removed from skin or surfaces with acetone, but expect itching later if skin is affected. These epoxies penetrate skin too, and can potentially poison you that way, or even through the eyes via vapor, so common-sense precautions are mandatory. Career use of it can lead to hypersensitization, but that's not likely to be the case with just careful incidental use. I've sure applied enough of it myself over the decades, so now am especially cautious. But it's safer than penetrating polyester solutions, more effective, and outgasses way faster.
My plywood/epoxy sink has been doing just fine with no need for fillets.
When I fitted my plywood (3/4" birch) panels together, I made sure to lay the factory edges on the face of the bottom deck - and applied waterproof glue to the joints prior to screwing them down tight (pre-drilled/countersunk pilots so I could do this quickly while glue was still fresh). This ensured maximal contact with no gaps...so that when I then I applied the epoxy (Rakka...like West but much less expensive), with two coats on vertical surfaces, and three coats on the sink bottom, this bottom layer was more than thick enough to ensure great coverage and glue to glue overlap along that (already tight) bottom joint.
Also note that I laid those factory edges on the surface face of the bottom perimeter, flush with the edges, (as opposed dropping them over the outside edges), so that there would be no chance of any gravity-caused shifting of that joint during the curing process, nor any separation issues down the road.
Here in earthquake country we have to make sure everything is especially well assembled and supported. But I always thought Smith's official darkroom sink leaflet demanding epoxy putty fillets was more about selling more of his product than anything mandatory in terms of joint leakage protection, especially after a couple coats of penetrating epoxy had seeped into those joints anyway. Would have been a good idea with common plywood; but since many of our local sinks involved long-term school and industrial darkrooms, they'd spend the recommended extra for true marine-grade plywood anyway, without voids in the ply. I haven't checked the price of marine ply post-pandemic; but a lot of sheet goods are now back down to pre-pandemic pricing. If you could find it at all, it was up over 400% a year ago.
All the photo labs per se used serious stainless sinks, never wooden ones. But for anything industrial involved wooden assembly, those would get coated with liquid Hypalon, still available at the time - nasty stuff; but those kinds of applications, like for concentrated acid vats, were directly underneath serious industrial venting devices anyway, and the applicators were wearing supplied air hoods like a deep-sea diver. At least it outgassed quickly.
I like Raka epoxy as well.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
May I change the question slightly? I have a marine plywood sink in my basement darkroom that I made maybe 15 years ago. It was sealed with West Products epoxy paint, and then a layer of deck paint. Recently it has started to leak along two seams. Is there any recommended way to reseal it that does not require me to disconnect it, bring it upstairs, and then reseal it in my backyard? IOW it would be simpler to reseal in place, but I don’t know if this is possible.
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