Author Topic: finish for a wooden sink  (Read 3827 times)

0 Members and 1 Guest are viewing this topic.

Offline bump

  • Posts: 45
finish for a wooden sink
« on: October 26, 2016, 04:06 PM »
hi experts,

I am going to build a wooden sink from a hollowed out solid block of cedar.
i have had plenty of woodcraft experts tell me not to, i hear what they say and i am doing it anyway.
my question is this, i want to make the inside of the sink waterproof.
i have spoken to some epoxy manufacturers who have all been extremely encouraging in the use of epoxy as a waterproofing medium for wood, however, none that i have spoken to make a foodsafe product. i was also warned that hot water can warp the epoxy finish.
it absolutely has to be foodsafe and i would rather it be temperature stable too.
the majority of use will be food prep with the occasional butchers block needing cleaning or pan that wont fit in the dishwasher.
does anyone on FOG know of a product which will be suitable?
i am not fixed upon the idea of using epoxy, other products are also up for consideration.
i am toying with the idea of using polyx oil if i cannot find anything else.
please don't suggest i make it from another material, i am aware of the possibility that my sink will crack and split, i am taking other precautionary measures to help reduce the risk; and to be fair, if it splits or breaks then i have only lost a bit of time and a block of wood, it's really not that important in the scheme of things. i will just re-evaluate my options should things go a little awry.

i am in the UK so products need to be available here or legal to import.

thank you to anyone with potentially helpful information. 

Festool USA does not pre-approve the contents of this website nor endorse the application or use of any Festool product in any way other than in the manner described in the Festool Instruction Manual. To reduce the risk of serious injury and/or damage to your Festool product, always read, understand and follow all warnings and instructions in your Festool product's Instruction Manual. Although Festool strives for accuracy in the website material, the website may contain inaccuracies. Festool makes no representations about the accuracy, reliability, completeness or timeliness of the material on this website or about the results to be obtained from using the website. Festool and its affiliates cannot be responsible for improper postings or your reliance on the website's material. Your use of any material contained on this website is entirely at your own risk. The content contained on this site is provided for informational purposes only and does not constitute professional advice.


Offline Angelo

  • Posts: 24
Re: finish for a wooden sink
« Reply #1 on: October 26, 2016, 04:35 PM »
Flex Seal clear. I am pretty sure it used to be, if not still is food safe. I used it in a similar application too what you are going for and it has held up for 2 years for me so far.

Offline RKA

  • Posts: 1004
Re: finish for a wooden sink
« Reply #2 on: October 26, 2016, 04:58 PM »
No experience here, but John's post triggered a (possible) concern.  Liquids and food stuffs going from the stove to the sink introduce a higher range of heat exposure (pasta water or hot oils/fats).  It may not matter if it's your house and you can control what gets dumped into the sink.
-Raj

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #3 on: October 26, 2016, 06:14 PM »
Self leveling bar top epoxies are one option. They should be food safe since bars serve food and beverages all the time. Honestly, cured epoxy is inert and poses no health hazards. Uncured epoxy far less so, and the hardener in liquid form is the main nasty part that people get reactions to more than the resin itself. Epoxy dust from sanding is also bad for your lungs. Once epoxy has cured, not much else to it. Sink water will be about 120 F on average. I know here in the U.S. most water heaters are usually set at peak of about 130 F.

You can also use a marine varnish, 3 coats minimum, as many as you want beyond that. That will add additional waterproofing. Let it be known, no epoxy is truly waterproof, it's just that the water migration is so small over such a long time that for all intents and purposes, they say it's waterproof.

I would say that coating ALL surfaces (top and underside) would help prevent cracking over the long haul. The dryer the cedar the better. Cedar will soak in a lot of epoxy the first 2 coats if rolled or brushed on. Again 3 minimum maybe 4 coats to waterproof.

Both epoxy and varnish do scratch a little so don't expect it to be a perfect finish all the time.


thanks for the info, do you mean varnish over the epoxy?
i was also pondering on how one might deal with vertical sides, perhaps set one side at a time?
will epoxy adhere to hardened epoxy? what i mean is: if i were to say set the bottom of the inside and leave it set, would a pouring onto one of the sides then adhere at the joint or would it be a weak point subject to water ingress?
point noted about the outside, i was planning to completely seal the wood all round as part of the process, it's nice to hear my thinking is sound in this respect.
being a boatman, are there any products you would recommend which would not soften in high temperatures, given that boats usually operate in cold water there is not normally call for them to operate under higher temperatures.

i enjoyed reading your response, it fueled further enthusiasm for my project. thank you.

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #4 on: October 26, 2016, 06:16 PM »
Flex Seal clear. I am pretty sure it used to be, if not still is food safe. I used it in a similar application too what you are going for and it has held up for 2 years for me so far.

i shall do some research into this product, thank you for the first hand experience and recommendation.

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #5 on: October 26, 2016, 06:20 PM »
No experience here, but John's post triggered a (possible) concern.  Liquids and food stuffs going from the stove to the sink introduce a higher range of heat exposure (pasta water or hot oils/fats).  It may not matter if it's your house and you can control what gets dumped into the sink.

good point...
i think with regard to water that it will not go much above 100 degrees anyway (as long as products can hold that heat) no matter what you do with it... in a domestic setting anyhoo.
with regard to pans etc, you raise a good point and one i shall have to bear in mind and educate others in the house, i hadn't thought about that until you mentioned it. thank you for raising my awareness.
it is in my own house, so a bit of collective savvy should help preserve it...

Offline Svar

  • Posts: 1255
Re: finish for a wooden sink
« Reply #6 on: October 26, 2016, 06:57 PM »
System Three S1 penetrating epoxy.
https://www.systemthree.com/products/s-1-clear-penetrating-epoxy-sealer
Don't know if its available in the UK.
You need penetrating type to prevent flaking. Kitchen sink gets more harsh treatment than bar top.
I was told by a boat builder (I can NOT independently confirm) that its food safe when cured. It was used, among other things, to seal wooden water storage tanks.
Being penetrating type it is very thin (consistency of diesel fuel) and soaks in quick and deep into wood. It will likely penetrate entirely through your cedar. Might require several applications. It makes wood water resistant in and out. It also takes quite some time to cure (more than a day) and it stinks!
You need to ask the manufacturer about its food safety.
« Last Edit: October 26, 2016, 07:01 PM by Svar »

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #7 on: October 26, 2016, 07:25 PM »
System Three S1 penetrating epoxy.
https://www.systemthree.com/products/s-1-clear-penetrating-epoxy-sealer
Don't know if its available in the UK.
You need penetrating type to prevent flaking. Kitchen sink gets more harsh treatment than bar top.
I was told by a boat builder (I can NOT independently confirm) that its food safe when cured. It was used, among other things, to seal wooden water storage tanks.
Being penetrating type it is very thin (consistency of diesel fuel) and soaks in quick and deep into wood. It will likely penetrate entirely through your cedar. Might require several applications. It makes wood water resistant in and out. It also takes quite some time to cure (more than a day) and it stinks!
You need to ask the manufacturer about its food safety.

awesome, thank you for your help.
it sounds quite an interesting substance.
i shall contact the manufacturer to see if it is foodsafe, heat tolerant and available in the uk.
i like the idea of it penetrating the wood completely, that sounds like a perfect solution; almost as if one is plasticising the wood fibres throughout.

Offline Svar

  • Posts: 1255
Re: finish for a wooden sink
« Reply #8 on: October 26, 2016, 08:00 PM »
P.S.
There are other epoxies similar to S1, I used S1 because it was recommended by a professional. The keyword is penetrating epoxy. They are often used to stabilize rotten wood (another search criteria). Keep in mind that unlike regular ones they contain solvent to reduce viscosity and facilitate penetration. As a result they shrink when cured, not much, ~50% or so. Tested it myself by placing small amount into a test tube and letting it cure.

Here is a good link: http://lumberjocks.com/topics/46168
You can contact shipwright, he's still active on that forum. Check his work while at it.
« Last Edit: October 26, 2016, 08:13 PM by Svar »

Offline Holmz

  • Posts: 4010
Re: finish for a wooden sink
« Reply #9 on: October 26, 2016, 08:56 PM »
You can cook an egg on a car bonnet/hood, so maybe a lacquer or 2-pack paint is food-safe?

After sanding and sealing the epoxy one could spray a clear 2-pack onto it or a lacquer.
I use deBeer which is a automotive 2pack, but I have not sprayed it over epoxied wood in a long time.
Lacquer has been used over a bunch of asian gear... (Bowls, plates, utensils) from "time-dot" 1.

We had a fellow at work that had a rare poisoning induced disorder. I think it was palsy??
They sent a person to watch his every move for a while.
He would take water out a 'sink' to make tea with like clockwork, and the water contained amines from an epoxy coating, even though the sink was filled with polished water.
The amines were playing havoc with him.

Personally I like epoxy, but I would be look at finding a lacquer for being foodsafe and dismiss the epoxy.

We should keep in mind that water is called the universal solvent for a reason.

No one has ever seen water change in a new testament sense where the atoms and molecules must become different. It needs to have something added to it, or be put up against something for the molecules to diffuse/absorb into the water, or collect gasses from the air.
Red water can be kept in wooden vessels for a long time, but it not end-grain wood. It is oak.
The liquid will only change from exposure to the wood or from the air.
Therefore taking a Kosher kitchen approach, and using a separate sink for food might make sense.

I am totally fine with people knowingly poisoning themselves with stimulants, depressants, hallucinogenics, psychotics...
Unknowingly poisoning one's self is something one should knowingly try to avoid.
So I would trust no one on how safe cured epoxy is. I would only trust an MSDS or some verifiable testing.
It it was a tub or hand or foot washing basin I would not hesitate, but a food sink you want to be sure.
...

If it was a raised bowl, then lining the inside with copper sheet/foil could be done. If you want wood exposed on the inside that approach will obviously be a fail.


1: "Time dot" Australian expression meaning the beginning of time just when time started and moved from zero, but before it hit an integer or natural number year.
« Last Edit: October 26, 2016, 09:04 PM by Holmz »

Offline Paul G

  • Posts: 1914
Re: finish for a wooden sink
« Reply #10 on: October 26, 2016, 09:31 PM »
Interesting project, if/when you complete it please update us on the process and results. I have no experience with such an application but I'd be considering the possibility of fiberglassing the surfaces for added strength. But like I said, your situation isn't something I'm familiar with.
+1

Offline Holmz

  • Posts: 4010
Re: finish for a wooden sink
« Reply #11 on: October 26, 2016, 09:43 PM »
Interesting project, if/when you complete it please update us on the process and results. I have no experience with such an application but I'd be considering the possibility of fiberglassing the surfaces for added strength. But like I said, your situation isn't something I'm familiar with.

^Nice^ mention...
Some of the thin tight weave fibreglass cloth is almost transparent when resined/epoxied up... Like a surfboard.

Offline Svar

  • Posts: 1255
Re: finish for a wooden sink
« Reply #12 on: October 26, 2016, 11:00 PM »
Lacquer has been used over a bunch of asian gear... (Bowls, plates, utensils) from "time-dot" 1.
Lacquer on asian lacqerware has little in common with lacqer you buy at a hardware store.

There is a number food grade FDA approved epoxies that meet NSF/ANSI toxicology standards. You just need to find out whether the one you use meets those standards.

Personally, I would not worry about it too much. You are not eating from the sink. If you worry about washing food there, then you should worry about any non-food grade surface you touch, as you might transfer toxins via your hands.
« Last Edit: October 26, 2016, 11:12 PM by Svar »

Offline Paul G

  • Posts: 1914
Re: finish for a wooden sink
« Reply #13 on: November 10, 2016, 05:04 PM »
came across this website today from an article in woodshop news magazine. While not a sink, certainly similar issues to deal with.

http://www.nkwoodworking.com/wood-bathtubs/
+1

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #14 on: November 11, 2016, 05:00 AM »
came across this website today from an article in woodshop news magazine. While not a sink, certainly similar issues to deal with.

http://www.nkwoodworking.com/wood-bathtubs/

thank you for the link, i have sent them a message and a link to this page, just wait and see what response i get and if they are will to divulge their process (fingers crossed).

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #15 on: November 11, 2016, 05:04 AM »
Interesting project, if/when you complete it please update us on the process and results. I have no experience with such an application but I'd be considering the possibility of fiberglassing the surfaces for added strength. But like I said, your situation isn't something I'm familiar with.

i will indeed record the process involved, i don't anticipate an easy ride and i expect to learn a few things along the way...
well, i live in hope that i do anyhoo...

fibreglass seems like a fair solution, however i want the finish to really pop rather than be muted because of the matting.

Offline Vondawg

  • Posts: 197
Re: finish for a wooden sink
« Reply #16 on: November 11, 2016, 07:14 AM »
+1 west system epoxy...I brush it into "warmed" wood ( carefully with a heat gun) to stabilize, sand to 220 and another to finish.
There are no mistakes....just new designs.


Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #18 on: November 11, 2016, 09:07 AM »
A couple of threads you may find useful to add to your decision. Posts from forum member Julian are quite interesting.

https://forum.canadianwoodworking.com/forum/woodworking/finishing-and-refinishing/1080224-oil-over-water-based-polyurethane-question

https://forum.canadianwoodworking.com/forum/woodworking/finishing-and-refinishing/1078839-satin-semi-gloss-epoxy-finish

John

thanks john, he seems like an interesting and knowledgeable guy, i joined up and sent him a message. just have to wait and see now. thanks for the heads up.

Offline Paul G

  • Posts: 1914
Re: finish for a wooden sink
« Reply #19 on: November 11, 2016, 10:05 AM »
came across this website today from an article in woodshop news magazine. While not a sink, certainly similar issues to deal with.

http://www.nkwoodworking.com/wood-bathtubs/

thank you for the link, i have sent them a message and a link to this page, just wait and see what response i get and if they are will to divulge their process (fingers crossed).

That would be surprising if they did. Seems almost a trade secret at this point.
+1

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #20 on: November 11, 2016, 01:41 PM »
came across this website today from an article in woodshop news magazine. While not a sink, certainly similar issues to deal with.

http://www.nkwoodworking.com/wood-bathtubs/

thank you for the link, i have sent them a message and a link to this page, just wait and see what response i get and if they are will to divulge their process (fingers crossed).

That would be surprising if they did. Seems almost a trade secret at this point.

seems that most respond as if it's a trade secret, i've messaged quite a few over the past year and got no response or an "i'm not going to tell you" response.
there was a well known artist in london that responded and divulged her process of using oils rather than resins, other than that i have mostly hit a brick wall or been informed the products are not food safe.
i don't mind, people have the right to refuse. it seems i get a better response from individuals rather than companies on the whole, but some are cool; including some epoxy manufacturers, however none so far have made a foodsafe product.

Offline Julian

  • Posts: 2
Re: finish for a wooden sink
« Reply #21 on: November 11, 2016, 02:23 PM »
Hi Andrew....so, I got your email on the other forum where I am more likely to be found and then came over here....which forum I have not browsed for a long time.

What you want to do is quite possible and epoxy is almost certainly the answer....but you need to define exactly what the conditions are that you are going to put the sink through.

What are you going to be doing with this sink?
Rinsing salad?
Washing the dog?
Cleaning your deep frier, baking pans and cast iron frying pan?
Cleaning veg?
Making cold soup, marinating the tough old steak?
Washing the dishes or the baby......What?

Will it be in daily use?
Will there be hot water (how hot?....epoxies do not like thermal shock.....but can withstand quite high temperatures (hotter than you want to get yours hand wet in) but they need to get there gently, so to speak or very nasty things can happen to the coating integrity.

Will you be using harsh or abrasive cleaning agents like Ajax, ammonia or chlorinated compounds (and if so why...stop that!)

I see a lot of talk in this thread about "food grade"...without much understanding (by some ...it would appear...) of what is meant by that, what the standards are and why....and anyhow, based on what you haven't told us I don't even know if food grade is a requirement or just a wish.....and (furthermore) fully cured modern clear coat epoxies are basically inert thermoplastic resins....perfectly safe. No heavy metals, no HAPS, no bad leachables etc etc.
But...lets cross that bridge once we get there.
You could always do the main work with epoxy X (which perhaps the manufacturer never bothered to send for the expensive food grade testing...since few people, for example, eat wooden sail boats but lots put them in water)...then topcoat with a verified NSF direct food contact epoxy if you so wished.
(By the way...Britain has different standards the we do over here in Canada..."NSF" refers to a common potable water standard over here).

Anyhow once you have filled in the blanks I'll see if I can provide some food for thought (pun intended.)

In the meantime I am more concerned about your great chunk of marvellous wood splitting ...so may I suggest you go check out Pentacryl or Wood Juice (http://www.preservation-solutions.com) as that will almost certainly be the first step prior to epoxy....and while you consider the excellence of that product then we can talk about which epoxy and why.

As a side note....why cedar?   Why not teak which needs virtually no treatment .....

Onwards to victory!

regards
Julian
« Last Edit: November 11, 2016, 04:02 PM by Julian »

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #22 on: November 11, 2016, 04:56 PM »
Hi Andrew....so, I got your email on the other forum where I am more likely to be found and then came over here....which forum I have not browsed for a long time.

What you want to do is quite possible and epoxy is almost certainly the answer....but you need to define exactly what the conditions are that you are going to put the sink through.

What are you going to be doing with this sink?
Rinsing salad?
Washing the dog?
Cleaning your deep frier, baking pans and cast iron frying pan?
Cleaning veg?
Making cold soup, marinating the tough old steak?
Washing the dishes or the baby......What?

Will it be in daily use?
Will there be hot water (how hot?....epoxies do not like thermal shock.....but can withstand quite high temperatures (hotter than you want to get yours hand wet in) but they need to get there gently, so to speak or very nasty things can happen to the coating integrity.

Will you be using harsh or abrasive cleaning agents like Ajax, ammonia or chlorinated compounds (and if so why...stop that!)

I see a lot of talk in this thread about "food grade"...without much understanding (by some ...it would appear...) of what is meant by that, what the standards are and why....and anyhow, based on what you haven't told us I don't even know if food grade is a requirement or just a wish.....and (furthermore) fully cured modern clear coat epoxies are basically inert thermoplastic resins....perfectly safe. No heavy metals, no HAPS, no bad leachables etc etc.
But...lets cross that bridge once we get there.
You could always do the main work with epoxy X (which perhaps the manufacturer never bothered to send for the expensive food grade testing...since few people, for example, eat wooden sail boats but lots put them in water)...then topcoat with a verified NSF direct food contact epoxy if you so wished.
(By the way...Britain has different standards the we do over here in Canada..."NSF" refers to a common potable water standard over here).

Anyhow once you have filled in the blanks I'll see if I can provide some food for thought (pun intended.)

In the meantime I am more concerned about your great chunk of marvellous wood splitting ...so may I suggest you go check out Pentacryl (http://www.preservation-solutions.com) as that will almost certainly be the first step prior to epoxy....and while you consider the excellence of that product then we can talk about which epoxy and why.

Onwards to victory!

regards
Julian

hi Julian,
thanks for calling over and sharing your wisdom.
ok, so here's where we are at right now.
we have a temporary stainless sink that we are using at present. we don't really use any caustic preparations of anything except once per week i bleach a temporary worktop i made from 100 year old bare pine floorboards. after bleaching i wash down with water and empty it in the sink. however, when the wooden sink is in use we will no longer be bleaching anything as we will have new kitchen worktops in place which will be coated in polyx oil.
chopping surfaces will be butchers blocks that will need washing in the sink.
most things in the kitchen are cleaned in the dishwasher in the pantry which is well away from the sink or worktops.
a few things will need cleaning in the sink such as roasting pans, wok, large frying pans and a couple of cast iron cooking pots that are way too big for the dishwasher or not suitable to go in there.
we never wash anything whilst it's hot.
at the moment we do pour some boiling water down the sink, from cooked rice, pasta or potatoes, however this could be emptied into a bowl to cool first if it's likely to mar the surface. it isn't a frequent thing as much of our cooking is one pot cooking (saves on washing up and clutter).
the wooden sink will be predominantly food prep. by this i mean cleansing unwashed veg.
we also discard copious amounts of coffee grouts down the sink.

temperature wise the hottest fluid is water, at or around 100 deg C. we never put oils of fats down the sink, either hot or cold. we don't seem to put hot pans in the sink either, tending to let them cool first before doing anything with them.

occasionally i do a small amount of washing up in the sink, not often as i don't care for hand washing too much, fairy liquid tends to upset my eczema. however when there is too little to put in the dishwasher and the house servants are on annual leave,  i do resort to manual labour.

the foodsafe angle came from research. i found that if one wants to produce foods for sale to others and use a wooden surface to prep on then the product used needs to be registered as foodsafe else it's illegal. so my thinking was that if this is required for food production then it has to be the safest type of surface coat. this being the case i want it in my home. it is not a legal requirement, moreso a personal requirement based upon using the safest products available on the market.
if "domestic" finishes are "less safe" then i don't want them. i would rather go industrial (it's probably far more durable too).

there will be nothing alive being washed in the sink. if it's in there and made of flesh then it's going to be eaten.
if our geese need tending to for unusual reasons such as cleaning cuts on the feet (only happened once) then they go in the bathtub. if they ended up in the sink they would be dinner; but they're my buddies so as likely to end up in the sink as the grandchildren...

the sink is used daily, i think mostly for washing hands, filling the kettle and disposing of coffee grinds; other things are more occasional use. i don't think we have ever left anything soaking for any length of time, maybe a pot used for mash soaking in cold water to stop the potato turning to concrete whilst food is eaten.

pentacryl is something i had in mind to help reduce the prospects of splitting. i had read somewhere that it can cause a greenish tinge, any thoughts or experiences of this? they claim not to do as such on their web page. i figured i would give the sink a good drowning in the stuff prior to working the wood, then after cutting the sink hole another drowning to make sure. then when i am ready to finish the surface, leave it dry out completely before coating the inside and out with finish product.

as a matter of interest, how would one surface the inside of the sink, one side at a time and complete with the bottom last or coat all inside surfaces at the same time? i presume there is a limited window for joining layers of epoxy so it adheres to itself?

thanks again julian, you're a star.

Offline bump

  • Posts: 45
Re: finish for a wooden sink
« Reply #23 on: November 11, 2016, 06:06 PM »

As a side note....why cedar?   Why not teak which needs virtually no treatment .....


regards
Julian

i forgot to answer this one,

cost primarily.
it's a bit of a prototype, in that i have never hollowed out a solid block in this manner before. i don't even know if i can do it effectively yet.
the block of cedar will cost me £60. in teak i'd be looking at 20 times that and wasting a huge amount of it by cutting it out and throwing it on the fire.
all the teak ones i have seen have been made from glued strips, i want a seamless chunk.
cedar looks good, is softer than teak so easier to work with, readily available locally, will match in with my single piece slab worktops (2 x 9 foot lengths 3 inches thick with wane on both sides) and it is more stable than oak (another local option).
if it breaks i won't cry, if i spent several hundreds of pounds getting a solid chunk of hardwood with no faults in it and i broke it then i would be tempted to shout at the geese. they shout louder than i do and would probably be offended; they might even decide to eat me or at least batter me senseless with feathers, and that just wont do!

Offline Julian

  • Posts: 2
Re: finish for a wooden sink
« Reply #24 on: November 13, 2016, 09:50 AM »
Well..     Good Day Andrew...and hallo to the excellent geese!

I have pondered the matter and I concluded that this is an extremely difficult problem and you will have to modify how you use your sink or your expectations.....or both.
What you really want is stainless steel performance in a tasteful looking wooden artefact....hmmmm!
You have a soft substrate, sometimes near boiling water (well, near 100 Deg C) and may from time to time let water sit or get trapped in there.....plus there might be periodic use of chemicals (bleach..whatever...).
And you want food grade.

Before we even get into what may or may not be done....an even greater factor is the natural tendency of wood (especially large tasty chunks) to move, split and crack over time.....sometimes quite a short time….like months not years....and this problem (which I will talk about more later on) should be addressed first and may in fact be the overarching factor in the whole deal here.
This is why people tend to use laminated wood (even if its the same piece, rift sawn, flipped alternately and glued back together)

Lets me deal with the "food grade” issue first.
Few coatings are "potable water grade"...even fewer are "direct food contact approved" and while some are "indirect food contact approved" (whatever that means!)... virtually none of these are clear coatings (read on....no-one in the food business wants a clear coat....they all want white....so they don't test or certify the clear…..its not that its worse.)
The actual reason for this limited selection is not that the rest of the coatings are a bunch of toxic mixtures sold by villainous and scheming weasels of weak moral fibre ....its very expensive to get the proper testing done and that "food grade" sector of the market is so small that the manufacturers just don't bother to spend the money......and it gets worse....typically you find that its only colour X and colour Y that is approved....because each pigment that is used must be separately tested (more money!)

The reality is that virtually all modern epoxy or polyurethane coatings (or oil or latex for that matter) are free of bad things (heavy metals etc, went out of favour decades ago) once fully cured....and anyhow you are not gnawing on the coated surface of your sink repetitively for years (at least, I hope not)...so lets you not be overly concerned about that aspect.....you are running water over it and down the drain….so who cares!

Now...your single greatest problem (well, besides, the weather, the wife and the geese) is the periodic use of really hot water.
Epoxies HATE thermal shock (and so will you)....and as epoxies are in fact thermo-plastic resins they will expand very swiftly while the substrate (your cedar) won't when hit with hot hot water...something has to give....and the coating either cracks or delaminates off the surface....then water can get in and your doom is apparent.
Besides which, at higher temps, most epoxies tend to get soft and easy to damage.
There are in fact a few (very few) epoxies that will withstand 100 deg C ...but not, understand......"ambient to 100 deg C in a split second" so be careful when some cheerful chap tells you his stuff is good to 100 deg, no worries. (You should worry yes!)

So much for the temperature issue.
You can have hot but not in a split second...ramp it up gently.

Now for hardness.
Your wood is soft (well, in terms of hardness) and when you wack it with the edge of the cast iron frying pan or the edge of a sharp object as may happen from time to time you may either damage the coating or cause minor delamination (under the coating) which in turn can lead to eventual failure.  This may not happen of course....but it may...then what...how do you do a spot repair before it gets wet and gruesome?

Chemicals.
Any harsh scouring chemical is to be avoided, likewise bleaches and strong oxidisers....these may not actually eat the epoxy but they can discolour or cloud it depending on the nastiness and the dwell time on the surface. A splashing or en passant usage is likely fine mind you, so you do have a bit of leeway here.

The problem with coatings is they are exactly that ..."coatings"...they go over the top and act as a protective wrap so to speak and everything depends on them being monolithic and staying that way......very very tough in your situation as neither the intended usage nor the substrate itself lend themselves to long term confidence.
If it was steel and you wanted to coat it (for the same usage) even that would be tough and give me pause (and I'm in the industrial tank lining business amongst other things… I can be found in refineries, chemical plant and nuclear facilities).
But cedar, in a sink that you actually use...whoa Nelly!   Lets not go there.

I would suggest that you consider a non film forming penetrating type of product that you can brutalise and not worry about, the worst case scenario being the need to clean it periodically or freshen it up with a bit more of (easily applied) whatever it was that you used in the first place.
Nothing to delminate, no film to fall off!
Woo hoo…..the true path to great success may be in sight!

But….first of all....you MUST address the "cracking and splitting issue".
Minimally that requires doing "the selected treatment" really thoroughly on all sides of the wood including the underside and drain hole etc....(thats what "all sides means..eh!)

Either you can do that with a penetrant like CPES, Pentacryl/Wood Juice, KwikPoly or Timbertect from http://www.conservationchemicals.co.uk/pages/aboutccc.html (who's website is worthless...so phone them).

You chose.
.
Or (actually “and/or"…read on) you can use a surface penetrant type oil, ranging from polymerised tung oil (the polymerised version dries way quicker).
Tung oil  was used by the Chinese 2000 years ago to keep their ships dry  when they had a navy, Waterlox (a well respected tongue oil variant) or a higher tech magic oil version such as Ligna Supra (which has …wait for it..... food grade approval from Canada).

You may say "why don't I use a deep penetrant like the first paragraph and then apply something from the second paragraph.”
Well, maybe thats a good idea and the way to go......I just don't know how any of the pararaph 2 products like going on to something other than wood. The tung oil/waterlox approach should be fine because you can put that on anything including your geese's feet and it will stick. Ligna Supra …I have no data…ask them....but my son in law uses it on wooden platters in his restaurant which are super hot washed and sanitized several times day and he says it works better than anything else he has tried on the platters (and thats under commercial usage conditions).

I would suggest that you rinse the sink after each usage and give it a cursory drying (standing water is the great enemy).
Touch it up now and again as required.....and if it does crack (again, first consider slicing up you block and gluing it back together) then you can dry out the damp in the crack with a hairdryer and fill it with a bit of something like thickened epoxy and prayer.

Regardless of what product or products you decide to use get in touch with the manufacturer and see what they have to say.
I can tell you right now that NONE of them will like you very much, all will be nervous and very conservative and hedging their bets as your intended usage is unusual and extreme and they will quiver with trepidation….but if you are nice and assure then that you understand its weird and isn’t recommended and you certainly have no intention of holding anything against them….but isn’t it an interesting problem…and what do they think….you may get some good pointers.

I sent you a PM with a bunch of links to such products and you can ruminate upon the matter at length.

Hope this helps.

best regards
Julian.

and....post a picture when victory is achieved.




« Last Edit: November 13, 2016, 07:07 PM by Julian »

Offline Shadytree

  • Posts: 24
Re: finish for a wooden sink
« Reply #25 on: November 13, 2016, 08:07 PM »
I've made several sink with an epoxy coating. As far as I know they are still in service, but those were bathroom sinks. I've made one kitchen sink. I was worried about the epoxy being pierced by a dropped knife or something similar so I made a vacuum chamber and infused the wood prior to assembly with a heat cured resin (cactus juice). Then a coat or 2 of epoxy for good measure. The people at system three were the only ones who would recommend the use of one of their products when exposed to boiling water. The tech guy suggested I use their clear coat bar top finish.