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Will a cottonwood cup hold liquid?

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Forum topic by bobasaurus posted 04-13-2015 09:45 PM 964 views 0 times favorited 15 replies Add to Favorites Watch
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bobasaurus

2679 posts in 2652 days


04-13-2015 09:45 PM

I want to turn a beer tankard/cup and am considering some cottonwood logs. Will cottonwood hold liquid with minimal finishing, or is it too porous? I also have a chinese elm log that might do the trick, it’s just harder to wrangle into a good-sized blank.

-- Allen, Colorado


15 replies so far

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johnstoneb

2150 posts in 1640 days


#1 posted 04-13-2015 11:03 PM

To hold liquid in any type of wood cup you will need to finish the inside. I would look at an epoxy. Once they are cured there isn’t much that will touch them.

Can you even turn cottonwood. The cottonwood I am familiar with is so soft and stringy it has got to be very dificult to turn.

-- Bruce, Boise, ID

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bobasaurus

2679 posts in 2652 days


#2 posted 04-13-2015 11:05 PM

It seems like denser woods will hold liquid mostly on their own, right? Unless the exposed end grain leaks water unexpectedly. I was hoping to go with a minimal food-safe finish, like mineral oil. I don’t want any excess epoxy resin/hardener leeching into the liquid. Waterlox is tempting, but I’ve mixed extra mineral spirits into mine and I’m dubious of the food safety now.

-- Allen, Colorado

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bobasaurus

2679 posts in 2652 days


#3 posted 04-13-2015 11:11 PM

Also, I wonder how crack-prone a full-log-width end-grain turning would be if I removed the pith and glued on another piece of wood instead. The tree rings would surround the cup opening then… I wonder if expansion checking would be an issue.

-- Allen, Colorado

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johnstoneb

2150 posts in 1640 days


#4 posted 04-14-2015 12:33 AM

I doubt that any of the woods would leak unless they cracked. It’s what is in the wood in resins, oils etc that will leach into the whatever is put into the cup affecting the taste. You need a finish that the alcohol and other chemicals in the drink won’t react with it. Once epoxy is cured you are not going to get any reaction from your liquid with it from any potable liquid. If you are worried about excess epoxy resin or hardener. The epoxy won’t cure harden with excess hardener. Wiping it out with denatured alcohol will remove any epoxy chemicals.

-- Bruce, Boise, ID

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Wildwood

1887 posts in 1602 days


#5 posted 04-14-2015 11:20 AM

I have not worked or turned with these woods but would try making a tankard/cup from both woods. Not sure about Cotton Wood, Chinese Elm looks like a better candidate still would make one of each.

I would opt for no finish first. Yes, some woods contain trace minerals and resins or silica, but all film finishes including epoxy contain chemical resins, solvents & driers. Point trying to make if tankard/cup holds liquids without a finish you are good to go! Cannot say how long that new tankard/cup going to last with or without a finish.
If you really feel safer applying a finish because that bad boy leaks like a sieve, okay. Use any finish you want except shellac. Polyurethane lot cheaper & easier than epoxy and might prove easier to apply an even coat inside the tankard/cup.

If going to use epoxy would look for a spray can product maybe less expensive than;

http://www.sears.com/eastwood-2k-aero-spray-aerosol-high-gloss-clear/p-SPM7968693625?prdNo=2&blockNo=2&blockType=G2

At the end of the day if want something can use every day buy a kit! Can find them at most woodturning venders sits!

http://www.woodturnerscatalog.com/p/54/5274/Artisan-Travel-Mug-Kit

-- Bill

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Tim

3119 posts in 1429 days


#6 posted 04-14-2015 11:40 AM


Once epoxy is cured you are not going to get any reaction from your liquid with it from any potable liquid.- johnstoneb

Bruce, that’s not entirely true. Epoxies can leach chemicals, particularly in warmer temperature liquids such as hot beverages. Here’s an article about epoxy leaching BPA:
http://www.ncbi.nlm.nih.gov/pubmed/12523782

I guess it depends on your level of concern over BPA, but it appears there are things labeled as food safe epoxy. And to be fair, I don’t know what the levels of BPA listed in that article mean. If you want to know more, leaching is the technical term so google epoxy leaching, etc.

I do recall someone posting a pretty good article that tested other common wood finishes as being food safe when cured. I don’t know if that would hold up to further leaching testing though.

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mramseyISU

419 posts in 1013 days


#7 posted 04-14-2015 03:11 PM

I don’t know about a cup out of cottonwood. I’ve cut down several that water runs out of like there is a hose bib in them or something. Also when it’s dry I think cottonwood smells like pee.

-- Trust me I'm an engineer.

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Wildwood

1887 posts in 1602 days


#8 posted 04-14-2015 03:27 PM

With more awareness of VOC’s and indoor air quality in the home. Awareness of toxic chemical resins, solvents, and dryer’s found in many wood finishes labeled food safe does not hurt to read warning and precautions on product labels or check out product MSDS/SDS before using.

I am from the camp no film finish is food safe! Others still maintain once a finish is dry you are safe! Yes, the FDA a long list of toxic chemicals they rate safe for food contact listed in their CFR. But not one wood finishing material!

Have been linking this article on message boards for many years.

http://www.finewoodworking.com/how-to/article/food-safe-finishes.aspx

Depending upon item (scoops, rolling pins & bowls) may use no finish or just plain mineral oil. On scoops & rolling pins don’t use anything finishing material. On bowls going to eat out of use mineral oil (laxative).

Almost of my bowls are finished with some film finish and labeled not food safe. Only do salad mixing & serving bowls on special order and all of those folks already know about reapply mineral oil as required. I provide them a small bottle which cost less than $2 at Walmart. Basically they get a refresher course, and know not to use baby oil or industrial/machine mineral oil!

-- Bill

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Rick M

7935 posts in 1848 days


#9 posted 04-17-2015 04:20 AM

When it comes to holding hot liquids or alcoholic beverages, I would play it extra safe. For years I’ve read about finishes being food safe when fully cured but there is a part of me that is skeptical. Months back I played around with making a coffee cup and tried 3 brushed coats of lacquer. I let that cure for weeks, a month or more, until I could leave it upside down for several hours then flip it over and not smell the lacquer. I put tap water in and within a couple hours it blew up and split open.

Next time I am going old school, will turn from greenish wood then boil in salt water, the way kuksas are made. Which reminds me … I need to try again.

There is a guy who makes cups from segments so there is no exposed end grain, but he seals them with epoxy.

-- http://thewoodknack.blogspot.com/

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bobasaurus

2679 posts in 2652 days


#10 posted 04-17-2015 06:01 AM

Never heard of salt water boiling, I’ll have to look that up. Does the salt add anything to the process?

I glued up some mahogany and walnut to make a blank for the cup/stein/tankard. They’re what I had on hand, but both woods are slightly porous. I think I’ll try a few coats of Waterlox to seal the grain and let it cure for a good long time with a fan blowing for ventilation.

-- Allen, Colorado

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bobasaurus

2679 posts in 2652 days


#11 posted 04-17-2015 06:08 AM

From the Waterlox website:

“Waterlox finished furniture is resistant to moisture, common household acids, alcoholic beverages and boiling water.”

We’ll see… I’ll report back my findings.

-- Allen, Colorado

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timbertailor

1592 posts in 892 days


#12 posted 04-17-2015 02:07 PM

I have had these cups for 25 years+ and they have been heavily used and still look and perform as good as the day they were made using epoxy.

-- Brad, Texas, https://www.youtube.com/user/tonkatoytruck/feed

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Rick M

7935 posts in 1848 days


#13 posted 04-17-2015 05:18 PM



Never heard of salt water boiling, I ll have to look that up. Does the salt add anything to the process?

I glued up some mahogany and walnut to make a blank for the cup/stein/tankard. They re what I had on hand, but both woods are slightly porous. I think I ll try a few coats of Waterlox to seal the grain and let it cure for a good long time with a fan blowing for ventilation.

- bobasaurus

I don’t know if the salt helps or not. I just remember reading in several places of people boiling kuksas in salt water and it worked for them. The salt may help pull additional moisture from the wood.

-- http://thewoodknack.blogspot.com/

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bobasaurus

2679 posts in 2652 days


#14 posted 04-17-2015 05:20 PM

Brad, are those aspen or maybe birch cups? They look nice with the bark on there. That’s kind of what I pictured for the cottonwood cups in terms of grain direction, though maybe without the bark. I’ll still try making a cottonwood one someday, but I don’t have time right now to let the green turning dry.

-- Allen, Colorado

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timbertailor

1592 posts in 892 days


#15 posted 04-17-2015 08:25 PM



Brad, are those aspen or maybe birch cups? They look nice with the bark on there. That s kind of what I pictured for the cottonwood cups in terms of grain direction, though maybe without the bark. I ll still try making a cottonwood one someday, but I don t have time right now to let the green turning dry.

- bobasaurus

They are made from Birch.

-- Brad, Texas, https://www.youtube.com/user/tonkatoytruck/feed

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