Any one epoxy better than another?
I had thought about a thin coat of epoxy, but didn’t know that varnish would stick to it very well. Being a beavertail this is to be a thin, light paddle for deep water. It SHOULDN’T (G) see many rocks, so I don’t want to load it up with coatings and make it heavy, but one coat (or two thinned coats) of epoxy would make me feel better about it. Is the home-improvement-store stuff in two tubes okay, or should I splurge on some West System packets? Should it be thinned somehow to penetrate the wood deeper on the first coat? Thanks again! Regan
Tough to Find Spar Varnish
I bought a custom Otter tail paddle last year and the maker recommended Spar Varnish. The Home Depot, Lowes, Woodcraft, trail here did not lead to any. Finally while looking for something else at an Ace Hardware I found some. This was after they told me they didn’t have it and tried to sell me polyurethane. I explained that the paddle maker told me polyurethane wouldn’t adhere to his finish. Then I kept scanning the shelf until I turned up the ACE brand Spar Varnish ACE 16375. They ought to be able to get it for you I’d think. It seems to be working fine so far.
It certainly went on easier than the Minwax “Clearshield” I used on another project recently. Maybe I got a bad can, but it was the consistancy of pancake syrup and of course the can said “Thining not recommended.” It was either thin it or daub it on with a putty knife!
Either one can work. Here’s why.
First off, the difference between traditional varnishes and polyurethanes is that the former uses natural oils and resins and the latter uses at least some synthethetic components. However, they are ALL still varnish.
Spar varnishes, whether natural or poly’, are formulated for extra flexibility. As long as you use a spar varnish it should work fine, regardless of which type you choose. Polyurethane varnishes tend to be tougher and more durable, but there’s enough variation between manufacturer’s formulations that there’s no hard and fast rule.
e[poxy
I would recommend a good epoxy resin usually used for boatbuilding. It is clear, easy to apply. The stuff in the tubes at the haedware is usually grey and is used as a glue or filler, not a coating. W.E.S.T, MAS, System Three, RAKA are all pretty good. Make sure you clean it up good after it hardens to get the waxy blush off the surface before finish sanding. It will clog up sand paper and cause problems with the varnish as well. I usually clean it off with denatured alcohol. The is some discussion about allowing the epoxy to cure for an extented time(up to a week) before varnishing. Epoxy cures to a mostly hard state in a few hours, but than continues curing slowly over time. I have in the past had varnish that took a week to harden when I applied it over epoxy applied the day before. I was in a hurry!
System Three
I use System Three Spar Urethane varnish, it is pricy but works great. Have tried Helmsman, Zar and Rustolium brand exterior, UV protected varnishes to save some money, but went back to the System Three.
Some varnish doesn’t work well with epoxy, if the can says cures in 4 hours and it’s still tacky in 4 days, they aren’t liking each other.
Mike
Summary of above plus my two cents worth
1. DO NOT thin epoxy - every manufacturer will tell you that it is formulated to work correctly out the pot and should not be thinned. Apply it in warm conditions to get it to flow thin - and use one formulated for coating. If applied in 70F and up you will not suffer from the waxy bloom that prevents further coating.
2. “Spar” varnish is pretty much a marketing term these days - used by Home marketing orientated varnish makers to make you think you are getting something that you are not. You are probably getting a pretty traditional shellac based varnish.
3. It is correct you want a flexible film on an item that will flex. Traditional shellac based and “traditional” one pot polyurethanes are better in this respect.
4. The more expensive marine based varnishes include far more U/V inhibitors than “home”" based products. U/V inhibitors slow down the breakdown of the varnish film, and the all important surface woodfibres which help the varnish adhere to the wooden substrate. On the paddle tha goes back in the car or bag at day end this is perhaps less important - on the hull of the boat -that may stow outside or in a windowed garage - this is vital.
5. If you epoxy coat first then you MUST varnish as epoxy has virtually no U/V resistance and will chalk and fail very quickly.
6. Two-pot varnishes perform extremely well - but as noted by someone else are hard and will tend to fracture on an item that flexes a lot. I also do not believe that many home builders have the means to apply two-pot safely which is actually pretty injurious to your health. See http://graemejwsmith.com/kayaks for more on this.
Sorry about the chemistry lesson but
I doubt that any mass produced varnish is manufactured these days using 100% natural products.
If you can forgive the basic chemistry lesson however I hope to clarify matters.
Originally varnishes were made from natural resins & vegetable oils.
The natural resins were obtained directly from trees( e.g. Rosin), dug up as fossil resins (e.g. Copal & Kauri) or were a result of a type of insect sexual activity (shellac) As can be imagined the demand for varnishes over the last 50 years or so meant that the demand for natural resins far outstripped the supply. The quality of the natural resins would also vary greatly.
The vegetable oils used are those having double bonds in the molecule which react with atmospheric oxygen to dry into a film. Linseed or Soya oils are typical examples.
For the last 50 years the natural resins have been replaced by synthetic resins of the type known as “alkyds”. These are produced from by products of the petrochemical industry such as phthalates & polyols. These are reacted together to form a resin. These resins are very brittle and only soluble in polar solvents such as alcohol. If during the reaction process oils such as linseed or Soya are included the result is a compound that can be used as a varnish when thinned with a hydrocarbon solvent such as white spirit.
The hardness and flexibility of the varnish depends on the quantity of oil included in the reaction. Higher the oil the more flexible but less hard.
Drying of the varnish depends on the number of double bonds in the oil molecule. These react with oxygen to form bonds with adjacent oil molecules eventually forming a dry film.
Polyurethane is a term used when isocynates are included in the product. In the case of air drying polyurethane varnishes the vegetable oil is reacted with isocynates & polyols instead of the phthalates & polyols. This gives chemical bonds that are superior for chemical & water resistance. The drying mechanism is identical however
There are various other types of polyurethanes that dry or “cure” by different mechanisms. These are:
Two components where the isocynate is mixed with a polyol prior to use. These have limited pot life and must be used within a short period of mixing.
Moisture cure (usually adhesives or sealants) where the product reacts with atmospheric moisture and must be kept in sealed containers prior to use.
I apologise if I have bored anyone but there is so much misunderstanding & also marketing nonsense about coatings I felt the need to illuminate these points.
Thanks…
I’m happt to be educated
regarding the chemistry. That said I think my real world points are still valid.
PS - Shellac is still fairly readily available at low cost. Once they stopped making 78’s out of it the beetles (whose body’s were used to create it) stll fly around and are harvested for furniture “French Polish”.
Good info, thank you. N/M
Check out Duron…
Paints. I’ve seen it in their stores before. I would imagine that it’s a little cheaper there than in a marine store.
Lots of good information!
I, for one, really do appreciate the information and explanations. I always like to know the “why” and “how” of things, as well as the “what”. Many thanks, take care! Regan
spar varnish
I bought a gallon of McClusky Man O’ War spar varnish for around $45.00 at the Dulux paint store.
Health Risks
Graemesmith is correct about the health risks involved in using epoxy resins. Allowing these resins onto bare skin can cause “sensitisation” Once aquired this is incurable and further contact with even minute amounts can lead to acute dermatitis.
2 pack polyurethanes can cause similar skin “sensitisation” issues.
A further concern involves spraying such products without proper ventilation and wearing an air fed mask (a normal filter mask is not sufficient) as the “sensitisation” effect of the atomised material if breathed will lead to asthma. A further exposure could then trigger an acute attack with the possibility of death !
Boiled linseed oil & varnish
I have had better results with boiled linseed oil than with varnishes. Varnishes chip off and so on. Uncomfortable on hands. Boiled linseed oil soaks in and seems to prevent substantial water penetration. I’m still using a paddle I made in the mid 80s.
Solution varnishes are easy to make. I’d tend to use seedlac and any somewhat softer resin in alcohol. Although turpentine works with many resins. And I’m always tempted to try acetone as a vehicle.
I make varnish all the time for violins. Easy stuff to do.
I prefer an oil-varnish blend
– Last Updated: Nov-01-04 11:46 AM EST –
I've been using a 1:1:1 solution of varnish (Epifanes, but it doesn't matter much), tung oil and turpentine. I much prefer the resulting softer, satin finish to varnish. This blend is a bit more durable and waterproof than straight oils (I've tried linseed and tung oils alone), but still breathes enough that it doesn't trap water in the wood.
The "solution varnish" you speak of sounds more like shellac than varnish. Can the resulting finish be re-dissolved with alcohol?
shellac
Seedlac = raw shellac.
Solution varnishes are things dissolved in a solvent. Dry by evaporation. Can be dissolved off the surface via a solvent.
Cooked varnishes cure and then cannot be dissolved with the vehicle solvent, if any was used. Polymerization is what I think happens.
Some hybrid varnishes. Will dissolve for a while, but then polymerize and shrink down. Mastic and linseed oil with a turpentine vehicle, for example.
The mix of oil varnish, tung oil, & solvent seems promising. I have some over-age varnish I can cut that way and try.
Steve
Finish properties
– Last Updated: Nov-02-04 8:25 AM EST –
"Seedlac = raw shellac."
I should have know that.
"Solution varnishes are things dissolved in a solvent. Dry by evaporation. Can be dissolved off the surface via a solvent."
Ah, therin lies my confusion. My understanding is that if it can be dissolved by the same solvent that was used to thin it, it's not technically a "varnish". I may well be mistaken about that. In your business, is "varnish" used as a generic term for a transparent finish, rather than denoting one with a specific type of curing process (curing vs. drying)?
"Cooked varnishes cure and then cannot be dissolved with the vehicle solvent, if any was used. Polymerization is what I think happens."
That's correct.
"Some hybrid varnishes. Will dissolve for a while, but then polymerize and shrink down. Mastic and linseed oil with a turpentine vehicle, for example."
What exactly is "mastic"? I'm not familiar with the term, other than in reference to "mastic" used as an adhesive.
"The mix of oil varnish, tung oil, & solvent seems promising. I have some over-age varnish I can cut that way and try."
That sounds like a good use for it. I use turps in my blend simply because I prefer the scent to the odor of mineral spirits. It adds to the sensory experience of finishing a paddle. ;-)
Nomenclature
Not suggesting they are relevant in the USA.
A coating that can be redissolved in its solvent is a “laquer” It does not react with anything to form a film.
Oils like linseed & Tung react with Oxygen to form a crosslinked coating. This drying mechanism is identical to the way varnishes dry.
A mastic is a sealant but could be an adhesive (although not a stong one like an epoxy)
Same here
That’s pretty much my understanding of standard finish terminology.