Epoxy and Varnish?

[Key]

I am building a new bowsprit out of Sitka Spruce, and was told that this wood is not very water resistant. My brightwork refinishing leans toward the classical approach using only varnish, but I bought West system resin with 207 hardener and plan to apply it in three coats, followed by several coats of varnish. I am a bit nervous about doing this because I have put so much work in the sprit so far...have no experience with this technique or with Sitka spruce, and do not want to risk ruining what is turning out be a beautiful piece of woodwork. Is this a safe and effective technique? Or, should I stick with the tried and true method of using my old standby Interlux Schooner #96 in 8-10 coats? Or, maybe consider just applying the West System on the bottom where the sprit rests on the deck for water protection and is not visible? Any advice for a newcomer to this site and a novice with epoxy applied under varnish?
Many thanks.
Key

[JimD]

Someone may come along and tell you that epoxy is not necessary and I can't say that it is but if you decide to use it then varnish does very well over epoxy in my experience. Clean and light sand the epoxy after curing to give the varnish a surface it can hold on to. The uv blocking ability will protect the epoxy which must have uv protection.

[wyndham]

I think you'd be better off applying a good soaking with CPES. The sprit is going to flex and the epoxy is going to crack and the varnish is going to crack with the epoxy and then you've got water wicking under the epoxy. The CPES will protect the wood, varnish likes to stick to CPES and you will have a lovely bowsprit.
Apply the CPES until it stops being absorbed. Let it cure for good couple of days. Lightly sand it and apply again. Lets it cure and then varnish away. Then take pictures and post them so we can see what a great job you did.

[Dale R. Hamilton]

Key- yes do use epoxy. Here's how.

If you plan on a wood stain, do this first, Pettit's 7666 always worked well for me (on mahogany). Let dry well. Cover with epoxy now- The WEST system would not be my choice- too thick for good penetration. Instead I like System Three clear coat- its crystal clear and quite liquid. Apply several thin coats with either a foam roller or brush. One technique is to roll it on and tip it off lightly if bubbles form. No need to sand inbetween coats. Apply several thin coats let dry good. Now, if you have an uneven surface, sand it out with 220 grit and a wood block- you will see the surface go dull when level. Don't sand thru you epoxy. Finally, tack the surface and apply 3 or 4 coats good UV containing varnish as usual. It should be perfect.

[Bob Smalser]

Occasionally when I need a hard finish on soft woods I use unthickened West epoxy, and gently play a heat gun over it to thin it to the consistency of CPES to soak in.

http://pic3.picturetrail.com/VOL12/1104763/4518261/57033887.jpg

Been doing that for 25 years and have never had a finish crack. Then I clean off any amine blush, sand out any bubbled from offgassing (they can be filled with thick cyanoacrylate to cut down on the sanding) then apply varnish.

Saves me from buying very-expensive CPES....which is probably 5% epoxy and 95% cheaper solvents, acetone being most of it.

The end result looks OK:

http://pic3.picturetrail.com/VOL12/1104763/4518261/57815588.jpg

Otherwise on most woods, I wet sand the wood with a 50-50 mix of Daly's Teak Oil and boiled linseed....let that dry...then coat with varnish. Saves several varnish coats and looks much better than varnishing over epoxy or using just pure varnish...the crystallized linseed inthe wood pores has a sparkle to it you don't get anywhere else:

http://pic3.picturetrail.com/VOL12/1104763/7483424/97909701.jpg

[ 06-29-2005, 10:33 AM: Message edited by: Bob Smalser ]

[Ack]

Bob, is there any advantage of using the heat gun on the epoxy over adding solvent to epoxy and then applying-- same as CPES only cheaper. Seems to me that the solvents may aid deeper penetration(??). I've never used the heat gun method, but I have mixed up my own self-thinned version of CPES and it seemed to work pretty well on the underside of some old longleaf I used for decking.

[Bob Smalser]

Adding solvent to epoxy weakens its strength in direct proprtion to the amoutn of solvent.

My heat gun technique is more akin to a 3oz glass job than it is to CPES.

[Ed Armstrong]

Bob,

That's nice looking wood! Do you use 207 hardener with West epoxy, or just the standard 205/206? I've been planning on finishing the transom of my Acorn dinghy with West epoxy and 2015 varnish, and I already have plenty of 105 & 206. I'll buy some 207 if it is necessary but would rather not, if I'll get an acceptible finish without it.

TIA,

Ed

[Bob Smalser]

I use both, Ed.....I don't think it matters so long as the resin hardens.

[Ed Armstrong]

Thanks. I'll try the 206.

In your recent post on your spectacular Chamberlain, you mentioned that you used Kelly-Moore's Tred Coat on your hull. I considered doing the same for my Acorn, but I also need to paint the bottom of my Typhoon (production fiberglass sailboat) as well as to seal the bottom of a concrete fountain. The Tred-Coat says that it's not for surfaces that have standing water. Have you used any of their other epoxy-based products for hulls that stay in the water?

My apologies to Key for hijacking the thread.

TIA,

Ed

[westinghouse]

Bob you bring up something that has been bugging me all week. This 'penetrating epoxy' concept seems to go around endlessly in circles. I was reading the label on Industrial Formulators S-1 during a slack stretch at the shop last weekend and see that they brag about their "50% solids"-which I take to mean 50% acetone etc. I've read the Gougeon's book and Epoxyworks and I've found that the Brothers (like yourself) have been saying for 25 years that thinning epoxy is the wrong way to go. I was hoping that the much revered Smith's CPES was 100% solids (otherwise it falls under the snake oil category).

So I'm wondering in earnest if you're generalizing using Smith's as an example (and I have no reason to think that's the case, I'm just covering my bases before I begin to reconsider my barely informed take on the CPES thing). I was actually thinking about finding a source for Smith's for the store, but if it's just another brand of snake oil, forget it.

Any have an opinion on using Gougeon's Pro-Set? Stuff's super thin and I think it's 100% solids (because Gougeon has been so vociferous against thinning their products). Seems like the answer to the boatbuilder's need for penetration (wait, that didn't come out right...)

Cheers,
Eli

[ 06-30-2005, 07:57 PM: Message edited by: westinghouse ]

[Bob Smalser]

I'm not your guy on goos....bet I haven't used 10 gallons of it in my lifetime. But FWIW:

All I know is that to treat any potential rot remaining in that dory bottom I bought a small CPES kit from Fisheries Supply....and wasn't impressed. The smell is stronger and sharper than acetone, with a tinge of trichloroethylene...the stuff seems to be strong solvents with sufficiently little resin that it's no longer adhesive.

I think I know why it is made that way, too. Heating epoxy thins it dramatically but the wood offgasses occasionally, leaving bubbles that have to be sanded out or filled.

[westinghouse]

After that post I went to Smith's site to check it out. Sure enough, it's epoxy thinned with solvents (they use fancy language like 'suspended in solvents'). I know what you mean about the bubbles from off gassing. The best recipe for penetrating epoxy remains: first coat heat-thinned; second coat unthickened; then, if you have to use CPES, use it as a third coat to prime for varnish. Sorta puts the whole Epoxy/CPES thing into perspective, labor wise.

Eli

[StevenBauer]

Or you could use Robb White's method. He cranks up his wood stove and gets his whole shop as hot as he can, like 120 degrees. Then he slathers on the epoxy and cools the shop down with a big old air conditioner. The epoxy just gets sucked right into the wood and no bubbles!

Steven

[Bob Smalser]

Originally posted by StevenBauer:
Or you could use Robb White's method. He cranks up his wood stove and gets his whole shop as hot as he can, like 120 degrees. Then he slathers on the epoxy and cools the shop down with a big old air conditioner. The epoxy just gets sucked right into the wood and no bubbles!

StevenHe builds itty bitty boats, tho.

[westinghouse]

I thought about the White technique, but, even if he said there were no bubbles he is notorious for his 'creative prowess'. And, as noted, his jobs all fit into his shop.

That said, I had an experience epoxying my decks in frigid weather and found that turning up the heat inside the boat made a substantial difference: the fast cure wasn't setting up at all without heat; with heat it was hard in a day. So say you're going to epoxy seal your cabin sides at the slip: crank up an oil filled radiant heater a couple of days ahead of time, warm up your slow cure smoodge and use a hair dryer on the wood. Leave the heater on and nature will take care of the rest.

Whatever, my point is this: bubbles are a sign that the cooling process either happened too quickly or was too extreme. Slowing down the cooling time is bound to make a difference, and that's what White does by heating up the shop (the air conditioner might be necessary in Georgia, but it's counterintuitive up here in the PNW). For every job there are bound to be a few different ways to get the same effect without resorting to diluting your epoxy.

Eli

[ 07-04-2005, 09:19 PM: Message edited by: westinghouse ]

[rmiller3]

"bubbles are a sign that the cooling process either happened too quickly or was too extreme."

I think it's the opposite, really. Epoxy outgasses on the rising temperature.

So... by all means, warm the wood and epoxy if temps suggest the need, and then let the shop/wood cool a bit after application, and bubbles will not form. In summer, applying epoxy later in the day while things cool off in the following hours accomplishes the same thing. Applying in the early day when temps are forcasted may result in outgassing and bubbles.

Robert

[ 07-06-2005, 06:33 PM: Message edited by: rmiller3 ]

[westinghouse]

Right, exothermic, cures hot. I was thinking of curing and cooling as the same thing.

[Stan C]

I've heard that it is the atmospheric gasses within the wood that "outgas" after applying epoxy and this can cause cracks or pores to form and these then will become pathways for water ingress. It would seem then that heating the wood to a temp higher than will be seen in normal use before applying epoxy which is then sucked in during cooling is the ideal, if it is feasible for the particular project. Can anyone add to, clarify, or refute this idea?

Also, is it as critical as I've heard that no water get into epoxy sealed wood (because it may never get out again?).

SC

[westinghouse]

Yeah, that's what I was picturing as well. White figures that the cooling wood expands and draws the epoxy in. This is tied to the idea that cooling too quickly (not the epoxy so much as the substrate)is more likely to cause bubbles - an idea I haven't abandoned. And I guess it's as important as you make it. Unthickened seal coats are easy enough to apply over the initial penetrating coat. Seems like good economy to me.

Eli

[wyndham]

There's a flaw in Whites logic I think. Cooling wood expands? So heating wood shrinks it? Something doesn't add up.

[AlanWS]

The other option is something like System 3 clear coat, which is a 100% solids epoxy that is thin and soaks in well without heating. It takes a long time to cure, which is either good or bad depending on what you need.

[Figment]

The only times I've ever had trouble with varnish over epoxy were the times I didn't give the epoxy ample time to TRULY CURE ALL THE WAY before applying the varnish.

As a casual observation (with zero hard data to back it up), it seems to me that old-school traditional varnishes have more trouble with epoxy than the newer polyurethane-based products.

[JimD]

An article from WB a few years ago on Robb White was a good read. He preheats the boat shop and boat to be epoxied to stifling temps and then applies the epoxy. Then lets the shop and boat cool afterward.

[westinghouse]

wyndham that's a good point. I'd like to think the flaw is in my interpretation rather than White's logic. He does have someone from MIT on his side endorsing the technique as being equal in terms of penetration to vaccuum bagging.

To get back to varnish and epoxy, I think the 100% solids thing is crucial. Epoxy breaks down in UV and I don't believe any varnish provides 100% UV protection. Cutting epoxy with solvents is like kick-starting the deterioration process.

That puts the System 3 clear coat high on the list, or if you gotta have Gougeon, check out ProSet. (WEST also has a clear hardener, but I don't know if it's runnier than the regular or not).

[Krueg]

I think what happens is whatever is in the pores of the wood contracts as it cools thereby drawing in the epoxy. That's the way I picture it anyway.

[wyndham]

I've been pondering the whole heat the wood apply the googe thing. If the wood has any moisture in it, which it must, then heating the shop and the wood would seem to me to drive the moisture out of the wood thereby creating voids, or more correctly leaving empty pores. Applying the epoxy that is hot and thin then fills these emptied pores. As the wood cools the pores close and the epoxy is captive.
I think thats what is probably happening....maybe.....?

[Stan C]

I think that Krueg and Wyndham have got it right but would like to hear from someone who really knows the specifics, especially since I've just read that CPES does not seal out water.

SC

[AlanWS]

The wood should change very little with temperature, though air in the pores will expand as it warms and contract as it cools. But if you heat the wood throughout to 100 F, and then cool it to 60 F, the air in the pores will decrease in volume by only 7%, and airspace is only a fraction of the volume of the wood. So this is not enough to explain many bubbles. Water that evaporates will expand a lot more. Warming can help dry the wood.

I think the major reason warming helps is that the epoxy becomes thinner, so bubbles can escape. Any bubbles that form from wood outgassing or any other reason while the epoxy is thin enough don't cause a problem. But warming also causes faster cure, and cure releases heat, so thick sections of epoxy can take off, in the extreme heating enough to char. Except for that, real epoxy (excluding CPES) should not offgas on curing.

Localized heating on curing epoxy can cause bubbles, probably by getting the wood hot enough to vaporize water at a point when the epoxy has thickened enough to prevent bubble escape.