Need to make Oak waterproof...In the name of science!

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Forum topic by ScienceGuy posted 06-24-2010 06:56 PM 9912 views 0 times favorited 15 replies Add to Favorites Watch
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2 posts in 3062 days

06-24-2010 06:56 PM

I just joined after reading a forum post about someone wanting to use wood for a sink ( I’ve been combing the web looking for ways to make some oak waterproof.

Here is the story. I am a scientist who studies mosquitoes and one of the habitats I work in are something called tree holes (basically rotted out holes in trees that hole water and where some species of mosquitoes breed). For some upcoming experiments I wanted to make replica tree holes out of oak logs. I cut 10” segments of Oak (about 9” diameter) from some recently felled trees (so this is green wood). I planned to cut holes in the top that were 6” diameter by 5” deep (so they would hold about 2 liters). The cutting has been difficult, but the bigger issue is that when I add water to the holes, they leak. There are probably two explanations…one is that there are very small cracks in the center of the logs, and the other is that the anatomy of the wood is such that it wants to conduct water downwards. So I need a way to seal the bottoms of the logs so the water in the hole does not leak out (for 2 months or more while the experiment is taking place). I cannot put any chemicals on the inside of the hole as it might make the aquatic environment toxic (and I actually want the mosquito larvae to live). I thought about using poly but the cracks are probably too wide (about 1/16”) to be properly filled and I don’t know how long the poly would stand up. I also thought about spreading a thin layer of silicone on the bottom but I worry about the durability over time. The other idea was to put a rubber “boot” (a piece of pond liner or similar) on the bottom and secure with a hose clamp (but the bark on the outside of the log make not allow for a watertight seal). Any solution does not need to be pretty, but it needs to last and hold up to the elements (although the sealed end will be on the ground).

Any thoughts would be appreciated.

15 replies so far

View miserybob's profile


88 posts in 3213 days

#1 posted 06-24-2010 07:35 PM

You could look around on a boating site like Jamestown Distributors. They (and I’m sure other places) sell a penetrating epoxy sealer that ‘might’ do the trick.

That, in combination with Epifanes varnish is supposed to be a great outdoor finish.

You could just sit the ends of the logs in a dish of epoxy and let it harden.

View tyskkvinna's profile


1310 posts in 3155 days

#2 posted 06-24-2010 08:00 PM

I was also thinking of an epoxy meant for boating.

-- Lis - Michigan - -

View flyfisherbob2000's profile


81 posts in 3156 days

#3 posted 06-24-2010 08:05 PM

different species of oak reacts differently to water. Red oak, although great for furniture, is not so great with water. It has a significant amout of capilary action, meaning water will “leak” out. To test this, cut a strip about 3/8” square, 6 ” long…. place one end in a glass of water & blow on the other end… you should see bubbles come out the lower end…. like a bunch of tiny straws bunched together.
Now, white oak has a closer grain, and not so much capiliary action, and doesnt leak near as much…. it tends to be used often in wine & whiskey barrells.
As for some sort of inner coating that isnt toxic to the little critters… maybe dripping melted parafin wax in the hole to seal it? Not sure how it will affect the mini vampires.
Also…. oaks contain tannic acid, just wondering how that affects the mosquitoes, meaning if the tannic acid leaches out into the standing water? What sort of oak trees in the wild do you find the naturally occuring pools?

View swirt's profile


3288 posts in 3141 days

#4 posted 06-24-2010 08:45 PM

There is a thick epoxy used for pouring bar countertops. That might work for covering the end and filling gaps. There is also a rubber coating used to coat tool handles (plasti-dip). It dries pretty quickly and is pretty thick so it could fill cracks.

-- Galootish log blog,

View ScienceGuy's profile


2 posts in 3062 days

#5 posted 06-24-2010 09:03 PM

I just went to the big box store and they suggested a marine sealant (comes in a tube just like silicone). It is suppose to seal wood “at or below the water line” so I am thinking that might do the trick. It cures in 24 hrs so I will see what happens.

flyfisherbob2000: Not sure of the species. The trees were in Mississippi and Live Oak and Red Oak are common at the site. The leaking seems to be out of very small cracks, and not via the cells of the wood. The tannic acid is not an issue since most mosquito larvae can tolerate pretty high concentrations (leaves are a major input into these holes and when they degrade the release lots of tannic acid into the water). Many deciduous trees form holes (Oaks, Maples, Cherry, Popular) but never evergreens.

View woodprof's profile


44 posts in 3359 days

#6 posted 06-24-2010 09:16 PM

What about gluing a thin layer of latex inside the hole (like putting a balloon in it)? Seems like that should work, unless part of your experiment needs to include whatever chemicals the wood might leach into the water. Although if that were the case, I imagine you would have to be a little more specific about the species of wood used.

View Seeharlez's profile


83 posts in 3162 days

#7 posted 06-24-2010 09:37 PM

I would try some liquid wax – like for car polishing. It will harden up and create a good barrier against water. You could apply it inside and out and realy drive it in to the end grain.

-- Greg - Vancouver, BC

View David Kirtley's profile

David Kirtley

1286 posts in 3167 days

#8 posted 06-24-2010 11:02 PM

The penetrating epoxy will probably not solve your problem as well. Generally, once you add solvents to thin it, it will make it more prone to water absorption.You will probably want two types of epoxy. A seal coat and a thickened epoxy for filling cracks and such. The thickened epoxy can handle 1/16 gap with ease. Good thing with the boats I make…. has some inexpensive epoxy as does Raka. You can get some pre-mix thickened epoxy like System 3 Gel Magic or Easy Fillet, alternatively, you can add fillers such as fumed silica to give it some body for gap filling. I believe just about all the epoxy’s that are commonly used for boatbuilding are also foodsafe (Don’t trust me, read the labels) and should not be harmful to your mosquitoes. (I sure hope you are finding ways to kill them…....)

-- Woodworking shouldn't cost a fortune:

View SNSpencer's profile


133 posts in 3282 days

#9 posted 06-24-2010 11:18 PM

Maybe line the “holes” with sap from the same species of tree? Or even some bees wax. Natural enough to have occured in the wild.

-- Jef Spencer - Refined Pallet -

View richgreer's profile


4541 posts in 3244 days

#10 posted 06-25-2010 12:26 AM

This project was just posted and it appears that the objective here was to make walnut waterproof. You may want to check it out.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View a1Jim's profile


117263 posts in 3746 days

#11 posted 06-25-2010 12:30 AM

Use a couple layers of pourable finish.

-- wood crafting & woodworking classes

View Mark Shymanski's profile

Mark Shymanski

5623 posts in 3882 days

#12 posted 07-03-2010 02:16 PM

I would think all of the man made finishes would enter enough of a variable to the environment that you could never be sure if it was the testing or the container that was inhibiting ‘natural’ behaviour. I think the paraffin or the beeswax sealer would be the least intrusive way to go. I’d opt for melting beeswax onto the bottom to seal the end.

-- "Checking for square? What madness is this! The cabinet is square because I will it to be so!" Jeremy Greiner LJ Topic#20953 2011 Feb 2

View davidpettinger's profile


661 posts in 3369 days

#13 posted 07-03-2010 04:34 PM

I would use bees wax. Beeswax has a melting point of 62 – 65 degrees Celsius. It has an acid value of 17 – 24. Paraffin wax is a petroleum derivative and may skew your tests.

-- Methods are many,Principles are few.Methods change often,Principles never do.

View Knothead62's profile


2596 posts in 3130 days

#14 posted 07-03-2010 10:30 PM

Why do you have to make them out of wood? Mosquitoes lay eggs in just about anything that will hold water; our pool cover is an example. Walmart, K-Mart, or any dollar store will have plastic containers. That should last for more than the two months.

View Jesse.R's profile


55 posts in 3094 days

#15 posted 07-04-2010 03:46 AM

i sure hope your studying to find new and exciting ways to kill those little winged demons…

-- jesse

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