Sanity check on my plans for a DIY darkroom sink?

Chuck1 · Oct 25, 2023

A pond liner might be good

Doremus Scudder · Oct 25, 2023

I'll chime in here too as well.

My sink is marine plywood with sides made of pine. Your basic materials sound fine to me.

I used marine topside paint for my sink. First put the whole thing together then primed. Then faired the corners with marine epoxy putty (MarineTex or similar). Then I sanded smooth and painted with glossy topside paint. Topside paint is fine unless you plan on keeping water in the sink for days at a time. If you drain it and let it dry between sessions, no problem. Topside paint is oil paint, so you'll need good ventilation. The upside is that it lies smooth easily. It's also easy to repaint; just sand lightly with wet/dry 120-grit sandpaper and add another coat later if needed. I repaint stained spots on my sink occasionally, I've never had to repaint the whole thing in 10 years. I did have to sand and seal up a crack once, no problem there either.

Do get a drain you can seal in well; that's the weak spot in the sealing. You may want to drill the drain hole first and prime and paint it on the inside and around the bottom a bit as well to make sure the wood is sealed there.

Best,

Doremus

BHuij · Oct 25, 2023

You're right - it's actually not PP, it's FRP, which is, I guess, fiberglass reinforced plastic. I did some Googling but was unable to find specifically which type of plastic we're talking about. Best I could find was "resin."

The reason I thought I'd be good to go with polypropylene is because I know if its chemical resistance. That said, I doubt whether I'll be pouring anything more scary than E6 blix into this sink. Maybe I'll get a sample and put it through some torture tests before committing to use it as my liner.

BHuij · Oct 25, 2023

Doremus Scudder said:
I'll chime in here too as well.

My sink is marine plywood with sides made of pine. Your basic materials sound fine to me.

I used marine topside paint for my sink. First put the whole thing together then primed. Then faired the corners with marine epoxy putty (MarineTex or similar). Then I sanded smooth and painted with glossy topside paint. Topside paint is fine unless you plan on keeping water in the sink for days at a time. If you drain it and let it dry between sessions, no problem. Topside paint is oil paint, so you'll need good ventilation. The upside is that it lies smooth easily. It's also easy to repaint; just sand lightly with wet/dry 120-grit sandpaper and add another coat later if needed. I repaint stained spots on my sink occasionally, I've never had to repaint the whole thing in 10 years. I did have to sand and seal up a crack once, no problem there either.

Do get a drain you can seal in well; that's the weak spot in the sealing. You may want to drill the drain hole first and prime and paint it on the inside and around the bottom a bit as well to make sure the wood is sealed there.

Best,

Doremus

I have no plans on leaving any liquids standing in the sink for more than a few hours during a print session. This sounds like a decent option. I'm not worried about VOCs or ofgassing during the curing phase, since I'll just build and finish this thing in my garage, and then bring it into the darkroom when it's cured and ready to go. Good advice on drilling the drain hole before painting to make sure I don't leave a bare wood surface anywhere that might absorb water/chems over time.

What primer did you use?

Bill Burk · Oct 25, 2023

Make sure to create a slope so the sink will drain.

Paul Howell · Oct 25, 2023

How about Pickup Bed Liner paint, first coat roll on, second coat spray. Not sure if it will adhere to wood.

DREW WILEY · Oct 25, 2023

I don't like raining on anyone's parade; but vinyl and acrylic deck coatings are neither as durable, even remotely, in that manner true rubber-based heat-welded ones are, but also tend to stain horribly, and have poor solvent resistance. And they weren't designed for "ponded" water either - that just puddles there for a long time (hopefully your sink has decent runoff angle anyway).

Epoxy paints are a more complex topic. Unless a penetrating marine liquid epoxy is used first, epoxy paint might spall or chip off due to brittleness. But these days there are DIY 2-part bathtub epoxies which are far safer to work with than the true old industrial types.

Lots of options out there.

cliveh · Oct 25, 2023

I think you are over thinking the problem. Why not use rigid PVC?

BHuij · Oct 25, 2023

cliveh said:
I think you are over thinking the problem. Why not use rigid PVC?

I'd love to have the sink made of PVC. How are you envisioning getting PVC into the shape of a 2x4' sink?

GregY · Oct 25, 2023

DREW WILEY said:
I don't like raining on anyone's parade; but vinyl and acrylic deck coatings are neither as durable, even remotely, in that manner true rubber-based heat-welded ones are, but also tend to stain horribly, and have poor solvent resistance. And they weren't designed for "ponded" water either - that just puddles there for a long time (hopefully your sink has decent runoff angle anyway).

Epoxy paints are a more complex topic. Unless a penetrating marine liquid epoxy is used first, epoxy paint might spall or chip off due to brittleness. But these days there are DIY 2-part bathtub epoxies which are far safer to work with than the true old industrial types.

Lots of options out there.

Drew, I've had two darkrooms for over 10 years with plywood sinks w drains covered w "Dura-deck" with absolutely no problems.

BHuij · Oct 25, 2023

I just got off the phone with my local Dura-deck guy. He said he's sure it would be waterproof enough to use for a sink, but he doesn't think it's practical to apply to a square-cornered sink shape, since it has to be folded in and heat welded.

The subtext I picked up is that the amount of $ he would make on a project of roughly 10 square feet didn't justify the drive

cliveh · Oct 25, 2023

BHuij said:
I'd love to have the sink made of PVC. How are you envisioning getting PVC into the shape of a 2x4' sink?

You can have it made to any dimensions you wish.

GregY · Oct 25, 2023

BHuij said:
I just got off the phone with my local Dura-deck guy. He said he's sure it would be waterproof enough to use for a sink, but he doesn't think it's practical to apply to a square-cornered sink shape, since it has to be folded in and heat welded.

The subtext I picked up is that the amount of $ he would make on a project of roughly 10 square feet didn't justify the drive

Too bad,.... in my case it was both fast and efficient (costwise)....compared to the cost of caulk, & epoxy and the time spent breathing fumes.

BHuij · Oct 25, 2023

Okay. After spinning around in circles on this and realizing there are probably a lot of right answers, I finally made a decision and placed orders.

I'll use 1/2" regular sanded plywood, give it a couple of coats of Bondo fiberglass resin to seal, then prime with Rustoleum marine primer, and paint with Rustoleum marine enamel. Ought to work just fine. Thanks all for weighing in. I'll document the build and post here when it's done.

DREW WILEY · Oct 25, 2023

Thanks for responding Greg, but experience with two sinks is still just two sinks, and for only ten years. I was right there when acrylic deck coatings were first developed just a street away, and for several decades after, often given samples to test by all kinds of makers and distributors of these even before they were being sold to the public. Most were substandard. I know the pros and cons, and the almost ubiquitous exaggeration of what such products can do. Better than nothing as a sink liner, but certainly not the best option out there either. Like I already stated, I've sold lining products to huge industrial operations, for aircraft carrier use, for many kinds of darkrooms, both private, commercial, and institutional - thousands of containers a month of penetrating epoxy alone, along with the biggest inventory of pro caulk by far of any retailer in the West. Not kidding.

I'm glad your sinks are working out well for you, but they might not for someone else. Needs differ somewhat depending on the exact chemicals encountered, the stability of the building and its surrounding geology, just how hard a sink get used, etc etc. That's why different options of construction and budget need to be considered.

I avoided mentioning the fiberglassing option because those resins can be pretty nasty to work with indoors. I've certainly done fiberglass laminations (outdoors), but have also seen its health effects on the careless.

btaylor · Oct 25, 2023

BHuij said:
Ought to work just fine.

This!

In fact, my sink is really more of a drip pan and work table than anything else, I’m not landing jets on it! While the end of my sink has a plumbed in drain, most of the true wet stuff goes on in the deep laundry sink right next to it. The high sides and height work best for me when I am dumping chemistry or washing film.

GregY · Oct 25, 2023

DREW WILEY said:
Thanks for responding Greg, but experience with two sinks is still just two sinks, and for only ten years. I was right there when acrylic deck coatings were first developed just a street away, and for several decades after, often given samples to test by all kinds of makers and distributors of these even before they were being sold to the public. Most were substandard. I know the pros and cons, and the almost ubiquitous exaggeration of what such products can do. Better than nothing as a sink liner, but certainly not the best option out there either. Like I already stated, I've sold lining products to huge industrial operations, for aircraft carrier use, for many kinds of darkrooms, both private, commercial, and institutional - thousands of containers a month of penetrating epoxy alone, along with the biggest inventory of pro caulk by far of any retailer in the West. Not kidding.

I'm glad your sinks are working out well for you, but they might not for someone else. Needs differ somewhat depending on the exact chemicals encountered, the stability of the building and its surrounding geology, just how hard a sink get used, etc etc. That's why different options of construction and budget need to be considered.

I avoided mentioning the fiberglassing option because those resins can be pretty nasty to work with indoors. I've certainly done fiberglass laminations (outdoors), but have also seen its health effects on the careless.

Of course I expected your comments Drew....but typical BW chemicals typically in trays with some splash potential. The Canadian Rockies don't have the same earthquake potential as California. What every works for you is fine, but allow those of us who've had a different experience also state what has worked for us.

Doremus Scudder · Oct 26, 2023

BHuij said:
What primer did you use?

I used marine primer. I think the brand I used for my sink was Rustoleum. There is usually a marine paint section in big-box home-supply stores. If you have a marine supply store near you, even better. There will be primer, topside and bottom paint in a number of colors. Get a quart of primer and a quart of glossy topside paint in your desired shade (I like white).

Best,

Doremus

DREW WILEY · Oct 26, 2023

Doremus - Big box Home Centers have ZERO true marine products. Why would they? Right now, even a quart of serious marine varnish costs around $150. We do have a number of real marine suppliers in this area, on the rim of SF Bay. I once handled a serious selection myself before retirement. Both the West Systems and Smith Epoxy plants are only about 10 min away from me. But home centers often do carry certain RustOleum neo-epoxy products potentially suitable for a darkroom sink, and possibly even polyester penetrants in lieu of penetrating epoxies. Their general paint products are generally crap however, despite the BS ads. And it would be darn rare to find anyone in a home center who actually knows what they're talking about in that regard. But the instructions on the can of RustOleum itself should be sufficient.

BHuij · Oct 26, 2023

Ended up going with Rustoleum Marine primer and enamel as well, although none of the big box stores around me had them in stock, so I ended up having to order them online. In any case, I'm hoping to do some construction next week. Between sealing with a couple of coats of fiberglass resin, priming once or twice, and painting 3-4 coats of enamel, I'm not particularly worried about the sink failing or its longevity.

At first I was worried I might have to do the sealing and painting with the sink in place in the darkroom, and rely on the bathroom fan to keep fumes down while things cure. Luckily, I've done the measurements, and I can fit the entire assembled sink, complete with legs, through the door to the darkroom. That means I can let the offgassing all happen in the garage with the door open before it ever comes into the house, which feels less problematic.

Now I just need to tear out the toilet and pedestal sink that aren't going to be used in that bathroom anymore...

Don_ih · Oct 26, 2023

BHuij said:
I'd love to have the sink made of PVC. How are you envisioning getting PVC into the shape of a 2x4' sink?

You can buy a sheet of 1/4" pvc, cut it with a circular saw, glue it up with pvc glue, caulk the corners with good silicone, and set it in a wooden frame to reinforce it. It'd beat the hell out of any painted plywood and take less time.

MTGseattle · Oct 26, 2023

The OP is past this now, but if anyone else is thinking about diy, or at least ordering something custom and you live in a reasonably sized metro area, check and see if there are any plastic specialty shops around. I'm not talking Tapplastics here, more like a facility with custom molding equipment. They may be willing to build something to your dimensions cheaper than a new Delta sink from B&H or whomever else sells them.

I heard a specific example of this recently, but his experience was from 20 years ago, so I would guess his sink would be at least 3x more expensive today.

An example for the extremely curious: PVC type 2. white. 0.187 thickness. 48" by 96" sheet. $250.

gordrob · Oct 27, 2023

I have and still use a 7 foot plywood sink that I got in the late 70s from a studio that had it built at least 10 years prior to that. It was painted with an oil based enamel paint and it lasted quite a long time. At some point a void appeared in the wood and filling the void and repainting it didn't really solve the problem. So my solution was to find some plastic and glue it to the frame and continue on. I thought the solid (could be acrylic) plastic mats that office chairs rolled on would do the job. Found two of them (about 1/4" thick) and cut them to fit and glued them to plywood and sealed all the joints. I was mainly doing black and white prints at the time and the fix worked great. No leaks no problems. The one day I needed to wash off the gelatine from a piece of matrix film at 130F. It didn't take long for the plastic to start to expand and the adhesive to start popping as it pulled away from the bottom of the sink. The bottom had been fitted to the sides so when the hot water hit the plastic it began to expand and bulge in the center. Pretty scary at the time as I didn't what was going to happen next. As the water temperature returned to normal the plastic contracted back to it's normal position. No leaks. The edge sealing held for some reason. I just have to be careful about what temperature of water I use in the sink. On the plus side if I need to rock a tray for some reason all I have to do is to put some warm water in the sink and I get enough of a bulge in the center of sink to rock the tray. Moral of the story is to watch which type of plastic or acrylic you use and how it is going to expand when you have it glued to the bottom of your sink.

Doremus Scudder · Oct 27, 2023

BHuij said:
...

Now I just need to tear out the toilet and pedestal sink that aren't going to be used in that bathroom anymore...

Keep the toilet if you can. It comes in handy for lots of things

Doremus

Doremus Scudder · Oct 27, 2023

DREW WILEY said:
Doremus - Big box Home Centers have ZERO true marine products. Why would they? Right now, even a quart of serious marine varnish costs around $150. We do have a number of real marine suppliers in this area, on the rim of SF Bay. I once handled a serious selection myself before retirement. Both the West Systems and Smith Epoxy plants are only about 10 min away from me. But home centers often do carry certain RustOleum neo-epoxy products potentially suitable for a darkroom sink, and possibly even polyester penetrants in lieu of penetrating epoxies. Their general paint products are generally crap however, despite the BS ads. And it would be darn rare to find anyone in a home center who actually knows what they're talking about in that regard. But the instructions on the can of RustOleum itself should be sufficient.

Well, the Rustoleum marine paints did well on my sink; still going strong after 10 years and good for many more. Plus repainting is easy. My local big-box store had a good-sized marine paint section, but we're close to a sailing lake here.

When I had my sailboat in Port Townsed, WA, there was an excellent specialty marine store there in the marina. Always needed lots of stuff to maintain a wooden sailboat Working on the boat is what prompted me to use marine ply and paint in the first place for the darkroom sink. I know how to maintain and repair it and know how long it can last with decent care.

Best,

Doremus

Sanity check on my plans for a DIY darkroom sink?

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