# Durability of Spar Varnish ... not on a Spar



## katalpa (Sep 14, 2015)

Hello, First post here - and wow what a wealth of good information shared. Thanks to all those whom contribute.

*Current Situation:*
A team I am working with has created a nice sturdy red-oak box (see attached images). The box will be holding filtered sand moistened with H20 for a geography teaching display. It will likely be bumped, brushed, and dinged by ages of young an old - so durability is an important factor.

The initially provided wood finish was a spar varnish.
We properly prepped up to 220 grit, thoroughly cleaned, and put an initial thin coat of the varnish on. After 24 hours it has dried relatively well, but I suspect (and hope) over the next few weeks and possible additional coats it will strengthen and harden even more.

*Question:*
Before proceeding with any further coats, is a spar varnish adequate?
Does the option of top coating with a more abrasive resistant finish sound like a better option than 2-3 more spar varnish coats?
Any other wise actions?

Thanks!


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## Steve Neul (Sep 2, 2011)

Welcome to the club. 

First of all red oak and water doesn't go together very well. It deteriorates pretty quickly and looks bad if water gets to it. The wood literally turns black from exposure to water. White oak would have been a better choice of oak wood to use. If it were me I would strip what varnish you have on the inside off and fiberglass it. Then you could use a spar varnish on the rest of it however there are different grades of spar varnishes and of course cost. What you need to look for is a marine grade spar varnish and the best is Epifanes. If it's too pricey or difficult to find you might use Cabot spar varnish. It's a marine grade spar and available at a lot of box stores.


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## katalpa (Sep 14, 2015)

@ Steve:
Thanks for sending some wisdom so quickly.
I agree, Red Oak is a 'thirsty' wood possibly causing negative effects rather quick. Expressed in this case by minor blackening from a wood glued Dado joint.

Regarding Fiberglass advice:
>> My experience suggests that the Fiberglass resin will need nearly all of the existing spar varnish removed. Is this correct, or would some residuals be alright?
Also, to prevent brittle fracturing of the resin 'bucket' inside box - would it be ideal to use woven glass matt embedded within?

Regarding Spar:
>> The current coat over the entire surface is the Cabot brand spar you mentioned, thus it looks like most of the prep. and application work committed thus far will not be lost.

@ All:
I'm worried about a junction of dissimilar materials though (varnish/fiberglass resin). Such might encourage damage to the susceptible wood sooner than not. Any advice on averting such catastrophe?


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## Steve Neul (Sep 2, 2011)

The fiberglass is a resin much similar to varnish but more waterproof. There shouldn't really be an issue lining the inside with fiberglass up to the top of the soil line and then finishing the rest with a spar. I would just stop the fiberglass cloth an inch or so below the transition line. Fiberglass resin is fairly transparent so it should blend very well. It just doesn't brush very smooth. 

You don't have to get the existing spar varnish off 100% where you are going to fiberglass but I would get as much off as possible. The fiberglass would just bond better to wood than the spar varnish.


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## katalpa (Sep 14, 2015)

@ Steve:

In the interest of maintaining some visibility of the oak grain on the interior of the box - would omitting the actual embedded glass matt in the resin be alright? Or would such being skipped lend concern of brittleness to the resin barrier?


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## Steve Neul (Sep 2, 2011)

katalpa said:


> @ Steve:
> 
> In the interest of maintaining some visibility of the oak grain on the interior of the box - would omitting the actual embedded glass matt in the resin be alright? Or would such being skipped lend concern of brittleness to the resin barrier?


Well, fiberglass resin is a pretty crummy looking finish for wood. It doesn't brush very well and is cloudier than varnish anyway. The fiberglass cloth won't make a huge difference in the strength of finish so if you wish to omit that, go for it. 

You can't clean the brushes either. You might pick up some cheap disposable brushes or foam brushes to apply the fiberglass. 

What really would have been better is if you could have found a plastic or fiberglass pan that you could just insert and then made the box to fit it.


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## Toolman50 (Mar 22, 2015)

Katalps
You've made a good looking box. 
I think you should now make a plastic or metal liner to go inside it to protect the box from moisture. 
I would not want standing moisture against Red Oak regardless of the finish you put on it.


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## katalpa (Sep 14, 2015)

The wisdom shared regarding the box interior has me thankful and concerned about protecting the Red Oak...

Currently my internal materials/coatings options include:
-Plate glass with silicon joints (likely very labor intense to get right)
-Lexan sheet with silicon joints (again, probably labor intense)
-Fiberglass resin coating

*Metal really isn't an option due to lack of tools and machining equipment.

I pondered some of those 'Bar Top' coatings often used. I helped coat several raw cuts of storm damaged trees on one occasion for a local pub, and the surface has stood up quite well to the friendly haggards who slosh their glasses in that place...
Does this sound like an additional option (based on experience)?


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## Quickstep (Apr 10, 2012)

I think a slight variant of the bar top resin is a very viable option. Epoxy, is generally favored by wooden boatbuilders. Sometimes they imbed mat and sometimes they don't. Epoxy however degrades when exposed to sunlight and needs to be coated with a UV inhibiting varnish like the Epifanes Steve mentioned. Costs will add up using this method as good epoxy and Epifanes are on the more expensive end of the materials scale. West Epoxy and MAS epoxy are used by many boatbuilders. 

Here's a link to a video from West Systems about barrier coating. You can find more info on their site.


http://www.westsystem.com/ss/barrier-coating-2/


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## Steve Neul (Sep 2, 2011)

katalpa said:


> The wisdom shared regarding the box interior has me thankful and concerned about protecting the Red Oak...
> 
> Currently my internal materials/coatings options include:
> -Plate glass with silicon joints (likely very labor intense to get right)
> ...


You might talk to a sheet metal shop. A square box shouldn't be very expensive to have fabricated.


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