Im having trouble building sinks for my darkroom. I started off with a frame of wood. Over that we put some stuff that the car repairer told us was fiberglass. It was too thick and we ended up with bumps all over the place. After sanding it down, (What a mess) It looked like a NASA moon surface simulator. Which would have been okay except - it leaked at the joints. So I filled where I thought the holes might be with silicone sealant. Still leaks. I went back to the bodyshop supplier and got some stuff that he called polyester. Its like clear paint. After mixing it in the correct order (to prevent an explosion - hey isnt this stuff fun?), I painted it on, it dried to a clear hard shiny finish and all the the drips were gone. ....except a couple. Which of course is useless. So - Ive got this pvc sheeting which they use here to put over table cloths. Its reasonably thick and quite soft. The only problem is getting it to sit in the corners properly. I dont want to cut it. That will ruin the whole point of an integral piece of sheeting. Its amazing how much water pressure there is in a 26x26 sink! My question is - before I stick this sheet in - which will be a little messy and hard to clean in the corners - is there a well-known international name for some product that I could paint all over this thing to stop it leaking? Many thanks to all - especially Mr Luong and Mr Greenspun et al for running a wonderfully useful service to the world community - Yaakov Asher Sinclair, Jerusalem, Israel

-- Yaakov Asher Sinclair (sinclair@actcom.co.il), July 12, 2000

Answers

FWIW, I have a sink made of 1 inch thick marine ply (strong enough that I can stand on it with no flexing).

The joints were waterproof caulked and it was painted over a few times with white marine paint (which is water proof).

No leaks so far - over a year and a half. (NOTE: I do NOT at any time fill the sink deep with water to turn it into a big tub and I don't think you would have reasons to do so either. My sink is large enough to handle four 20x24 trays side by side.)

I don't think you need to go the fibreglass way. Just repaint every few years or when the paint starts to wear.

Quite a few people have darkroom sinks like this.

The PVC sheeting way is not a neat idea for the long term.

-- K H Tan (kahheng@pacific.net.sg), July 12, 2000.

A few years back I helped a friend build a large darkroom sink out of marine plywood. He cut it very carefully so the edges were perfectly straight, caulked the seams as he put it together (we used screws), and then painted it with a heavy coat of polyurethane. It is still working fine.

-- Ed Buffaloe (edbuffaloe@unblinkingeye.com), July 12, 2000.

I have built a few darkroom sinks through the years and found that using fibreglass works well, but only if I used the normal resin and fibreglass batting. It is a bit different from auto body fibreglass as the rolls of batting are used in making boat hulls, etc. This makes for a nice, strong and waterproof sink. The marine plywood will definately add strength and help make a better sink, along with painting with the marine epoxy paints. Try redoing the sink and layering the fibreglass more smoothly, being careful to put a bit more resin in the corners. If you do it well you will have a very smooth surface that is waterproof. Check with a boat builder if you can find one as they will have working methods proven to be waterproof, quite a bit different from auto body repair. I have friends who have made sinks with the wood, paint & sealer and they also have success and use them for years. Good luck when you re- do your project.

-- Dan Smith (shooter@brigham.net), July 12, 2000.

Polyester is normally used to finish tables. It doesn't take well to water, after a short time it will dull and may seperate from the surface it is bonding to. As for the fibreglass, i don't know why that didn't work??? Are you using glass fibre cloth with the resin?

Another suggestion would be keep an out for restaurants that close down, i was able to pick up a large stainless steel sink for about $250! Dave.

-- Dave Anton (daveanton@home.com), July 12, 2000.

Without a well constructed sink you are going to chase leaks forever. I mean if the basic structure is not sound, has gaps at the joints, flexes or twists, your sunk. I built my sink using 3/4 inch exterior grade plywood. All the joints were reinforced with gussets, screwed and glued using a waterproof polyurethane glue. All exterior surfaces were painted with 3 coats of two-part epoxy paint and then a silcone caulk bead was run along all the inside seams. Was your sink good and tight before you started applying waterproof coatings? If not, you need to go back and rectify that problem.

-- Dave Schneider (dschneider@arjaynet.com), July 12, 2000.

You might try this if the leaks are at the corners or where the sides join the bottom: Go back to your fiberglass supplier and pick up some of the resin. Mix it with a filler as per instructions. Sandpaper the area of the corners and bottom joints and build up a little cove of resin at each joint. Use a plastic lid or cut a curve in a piece of plastic to use as a kind of squeegee to form the fillets. Once that is dry, your leak problem should be solved. This is the way they waterproof boat joints. The curved corners will also be much easier to clean. I would suggest putting a clear epoxy coating of the same epoxy you used to make the fillet over the fillet once it starts to harden. Just paint it on with a throw-away paint brush. Hope this helps.

-- Doug Paramore (dougmary@alanet.com), July 12, 2000.

I would rebuild it as per the above suggestions.On the one I made I used silicone on the corners and bottom for the adhesive,then screws for fasteners and finished with marine epoxy paint. No leaks. As has been said, the joints must be accurate and held tightly with screws. George

-- George Nedleman (gnln@thegrid.net), July 12, 2000.

There is a product sold by Benjamin Moore dealers in the United States called "Moorelastic." I think that is just their brand name for a product generically known as "elastomeric." It's a waterproof, fairly thick paint-like substance that you apply with a paint brush. It has worked well for me. I made (actually had a carpenter more skilled than me make) my sink out of normal Home Depot plywood. I didn't use marine plywood and it doesn't seem to have made any difference. I gave it about five coats originally and I recover the interior about every year, more to cover up the chemical residue stains that don't seem to wash off than out of any real need to keep it waterproof. I caulked the joints and corners with a waterproof caulk. Like someone else mentioned, I never fill the sink up with water like a bathtub, I just run water through and over it.

-- Brian Ellis (bellis@tampabay.rr.com), July 12, 2000.

After having water get under the fibreglass on my sink and blister the whole thing, I finally decided to make a renewable sink liner. I went and bought a sheet of heavy vinyl, like used for Jeep top windows. I did cut it into flat pieces for bottom, sides, and ends. I then used Lexel, a silicone with adhesive in it. It is great stuff, keeps my old cars from leaking, too. Anyway, with the Lexel stuff I thoroughly glued all edges and seems of the vinyl, mainly underneath. It works great. If it ever leaks, I only have to patch, or replace the one section. In any case, the wood underneath is not greatly affected. I used clear vinyl so I can see any leaks before they get really bad. The worst area on mine in the past was where the faucet hit the sink, which I had built as a wooden sink depression. That got changed to a bar sink, which did away with 99% of the trouble area. At this point, I am all for renewable sink liners instead of a big wet, gooey mess if it leaks.

-- E.L. (elperdido65@hotmail.com), July 12, 2000.

There are 2 types of resins, polyester, used for car body work and other non-marine purposes, and epoxy, the best and most expensive. Polyester does not bond to wood, and that's why your material separated. You can use fiberglass for the seams, in narrow strips about 2 inches wide, called fiberglass tape, and just plain epoxy on the areas away from the seams. First use cheap wood screws to assemble the sink, then cover the entire sink with resin, let it cure, then take care of the seams, a second or third coat should finish it fine.

-- Bruce Schultz (schultzredfish@aol.com), July 13, 2000.

As was noted in a previous post, polyester based epoxy is not meant for wood. Marine epoxy such as West Systems, System 3, or MAS is meant for encapsulating wood. None of the marine epoxies have an odor and you can easily clean up the wet epoxy with either alchohol, white vinegar, or a weak acetic acid solution.

I have built 3 wooden sinks - none of them have leaked. I would suggest that you construct a new sink using the following procedures and it will not leak.

Prepare the sides and sink bottom to the size you want. Using marine epoxy, coat all of the wood, including edges and let the epoxy cure. Some epoxies will have a wax-like "blush" on the surface after the epoxy cures. This must be sanded or cleaned off using acetone for the next step in assembly.

Prepare the edges of the sink and sides to be assembled. You can screw them together, or, if you have the tools, use a lock joint miter router bit. Coat the joint edges only with epoxy and assemble. Let the epoxy cure and you have now glued the sides to the bottom.

Mix up some epoxy with a filler material like micro-balloons so that the epoxy has a thick peanut butter consistancy. Use a tool like a tongue depressor stick (you can find those at craft stores they are called "craft sticks") and apply the epoxy paste to the joint inside of the sink where the side and bottom meet. You are making a fillet with the epoxy that will greatly strengthen the joint, and ensure that it will not come apart or crack from "racking" the joint as you lean on the sink side while you are working. Let the fillet cure. Wipe the entire sink down with acetone.

Mix up more epoxy and coat the entire sink with a final encapsulating coat of epoxy.

Now you need to paint the marine epoxy because it is not meant as a final surface material.

I would suggest that you use epoxy paint. You will have to go to an industrial paint store to find this type of paint. Put 3 coats of epoxy paint over the marine encapsulating epoxy.

You will now have a totally leak proof, water proof sink. The last one I made is now 25 years old and working fine.

-- steve (s.swinehart@worldnet.att.net), July 17, 2000.