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Stave core door glue for 3/16" veneer?

9/17/20       
T28c34 Member

Building a mahogany entry door 1 3/4" thick. I am making stave cores for the stiles and rails, and will be facing them with 3/16" mahogany. The entry door is facing the east north east, pretty far under the entry way overhang. Its in the northern Illinois, we get the worst of all seasons. I have been researching what glue to use to adhere the veneer with and pulling my hair out with all the different answers. I will been using a shop made press (two 5"x8' pieces channel iron and clamps). thought about Weldwood plastic resin. The staves are glued up with Titebond 2 and now after reading a lot of good and bad things mostly bad about Titebond 2 and 3, was that the right thing to use. I've always used Titebond 1 for interior work in my shop forever. So now leaning toward Ultra-Cat pre catalyzed adhesive. but guys are saying no because it uses water. So what about Unibond 800? So i'm confused now on which way to go.

9/17/20       #2: Stave core door glue for 3/16" ...
Gary

I typically use Titebond 2 Extend but the plastic resin would be an excellent choice since it dries HARD and STIFF which helps keep things straight. Make sure your press has absolutely no twist in it .

9/18/20       #3: Stave core door glue for 3/16" ...
Zach Member

I typically use West System. Never had a problem. I would also suggest resorcinol, but I hate having to turn the heat up to 70 degrees.

I agree with avoiding water based glue, as it introduces moisture to the core.

Have you considered solid stock?

9/18/20       #4: Stave core door glue for 3/16" ...
Jared E

I'm not sure I'm following the logic behind the argument against Ultracat. Because it uses water as a catalyst? If practical experience is worth anything, here's anecdotal evidence that it's tough enough for your door: Around 5-6 years ago I was contracted to built somewhere around 100 giant outdoor Christmas decorations, big heavy vacuum bagged laminations with Ultracat. They're pushed outside to endure 2 months of Pacific NW winter each year where they get all manner of gross weather and have held up beautifully with no delamination.

9/18/20       #5: Stave core door glue for 3/16" ...
David R Sochar Member

TB II is fine for the stave core. No worries.

I think it wise to avoid water base glue for thinner laminations, so that leaves solvent base glues - urethane, epoxy, resorcinol.

If you are not concerned with water, the plastic resin glue is excellent. Be sure it is fresh, and be sure the temps of everything is well above 70 degrees.

We have had bond failure with urethane. These can't be seen until it is out in the field and the phone rings... The failures are related to pressure - not enough in a vacuum bag. Clamping gets you to higher pressure for sure, but I am currently spooked.

That leaves epoxy. Which we use more and more of. It has almost everything going for it, except clean - up and cost.

But then, I'd just use solid wood, and avoid the questions altogether.

9/19/20       #6: Stave core door glue for 3/16" ...
Adam

Epoxy.

David,

Cleanup epoxy with vinegar or isopropyl alcohol(not denatured) Don’t use acetone.

I wouldn’t trust any of our exterior work to anything but epoxy. Plastic glue would be fine, but why? What benefit over epoxy does it have?

Cost of epoxy? Labor & wood look really expensive compared to a few ounces of epoxy.

9/23/20       #7: Stave core door glue for 3/16" ...
John Member

The water argument doesn't hold water in my experience. But creep resistance, heat resistance, and how much pressure is required to get an adequate bond are important. PRG has all the right properties and I've used a lot of it in my vacuum bag with no bond failures, including on 1/4" exterior door skins, but 14 psi is an order of magnitude less than recommended so I'm switching to Unibond 800, Polyurethane glue, or epoxy. All of them look to have the right combination of properties, but polyurethane may be the best overall.

John

9/24/20       #8: Stave core door glue for 3/16" ...
Rich S Member

I use plastic resin (urea formaldehyde) for all of my doors, including stave core exterior doors. I don't trust PVA glues in a humid environment (I'm in New Orleans) for millwork. Epoxy is great, but it is six or seven times as expensive. I believe there's no benefit to it in this case. My father was a wooden boat builder in Maine and we used a lot of West System epoxy, but I can also remember as a boy in the 70s, watching my father scarf planks together with "Plastic Weldwood" (the old DAP brand name for their plastic resin glue). I don't recall ever hearing of any glue failures and that was below the waterline.

9/28/20       #9: Stave core door glue for 3/16" ...
David R Sochar Member

John - We gave up on polyurethane glue in a vacuum bag due to poor adhesion - bubbles. The 14 psi was not enough to get the poly to bond.

9/28/20       #10: Stave core door glue for 3/16" ...
John Member

Thanks David; good to know. Then I'm down to Unibond 800 and epoxy. Most epoxies aren't great at high temperature so maybe the best choice is Unibond 800. I was hoping Polyurethane would be a good choice; it's the only single component option among the group.

John

9/28/20       #11: Stave core door glue for 3/16" ...
Adam

How hot are you planning on getting an entry door? Wooden boats are built with epoxy. Entire carbon/glass fiber boats are built with epoxy. Painted dark blue sitting in full sun.

We’ve built hundreds of entry doors with epoxy. Many garage doors. We only use epoxy for all of our exterior work. I’m talking 40 years worth of arch woodwork & boatwork.

TB3 has problems with heat. Epoxy has no downsides except for cost.

9/29/20       #12: Stave core door glue for 3/16" ...
John Member

Adam, I know it doesn't seem to make sense, and the history of epoxy with boats says they work, but the data for them isn't great. The creep temperature of System 3's T-88 is 119F and the max. service temp. is 160F, per their data. For West Systems' 105/206 the creep temp. is 123F; no max. service temp. is given but it must be similar. The stated max. service temp. for Gorilla Glue is 200F, for comparison. The strength of T-88 after 8 hours at 150 F is half of the RT strength, though still pretty high.

How hot does a house door get? Pretty hot if it's painted a dark color and gets sun on it. I measured 175F on a couple. I've seen plastic moldings melted on steel doors behind storm doors. Of course we shouldn't be putting storm doors over wood doors exposed to direct sun but people do what they want. I'm just trying to find the best glue to minimize the risk of failure. I've never had a failure with epoxy but only used it for the M&T joints so far. I've so far only used PRG for veneer skins and have had no failures with it either but I know I'm not getting enough pressure on it in the vacuum bag and would like to switch to something I have more confidence in. That product is probably epoxy but based more on historical performance than reported data, however. Nothing wrong with that, empirical data is the best, but my confidence would be higher with a product that checks off all the boxes.

John

9/29/20       #13: Stave core door glue for 3/16" ...
Adam

John,

Those numbers are not new. There is no such thing as creep with adhesives. We use the word to explain when a glue line becomes visible. For example, white pva is softer than TB1. As the wood moves with humidity the joints get tighter and the cured glue is squeezed produces a protruding glue joint. Softer the adhesive the more “creep”. TB1 no creep.TB3 lots of creep.

In mechanical terms creep refers to a particular stretching effect that happens in specific materials as you pull(tensile strength) on them. The most notorious one is Spectra/Dyneema plastic fibre. We use it for line on sailboats. Under sustained loads it will actually permanently stretch. Whereas Kevlar does not. Dyneema is stronger but we can’t use it for sails. Only line.

Epoxy will temporarily get a little softer when exposed to heat then completely regain its full strength. This process never causes adhesive failures. It has nothing to do with adhesion.

Forget wood epoxy. Masts of sailboats are made of carbon fibre & epoxy. That’s it. Often they are clear coated and sit in the sun all day. The rig loads are inconceivable. The Gougen Brothers(West System) were the largest builder of wind turbine blades in the world. They built them using their regular 105 resin.

We are talking about a front door. What do you expect the epoxy glue to do???

Epoxy temperature

9/29/20       #14: Stave core door glue for 3/16" ...
Adam

The blades were built primarily from wood with glass reinforcement.

9/29/20       #15: Stave core door glue for 3/16" ...
John Member

Thanks for your thoughts Adam.

John

9/29/20       #16: Stave core door glue for 3/16" ...
Keith Newton

To me, even though the Mahogany is a good stable wood, I would be concerned about going with 3/16''. Why not 1/16" instead. The thicker you go, the greater the stress on the glue lines, which can be so great that even if the glue doesn't fail, bits of wood can be torn off either side when there is enough mass. Probably like most woodworkers around the country that don't have a big marine supplier in the neighborhood, I started out using West System brand because of seeing their ads in the magazines. I hated that 5:1 ratio and pumps. I switched to System 3, then finally settled on FGCI linked below. I like the VERY FORGIVING 1:1 mix ratio. Instead of pumps I usually place 2 equal size Solo cups side by side and pour equal amounts in each then mix them together. I add colloidal silica while stirring to get whatever viscosity I desire.

If JB Weld is good for 300º there must be others that can withstand more.

When I hear people complain about epoxy being too expensive, I have to wonder how cheap it has to be? The FGCI cost around $140 for 2 gallons, which is about $100 less than the West brand. I have no affiliation with this company, just a very satisfied customer for about 25 years.They have good tech support if you need advice also.

FGCI Resins-Polyester-Vinylester-Epoxy

9/30/20       #17: Stave core door glue for 3/16" ...
Adam

John, I’m not trying to convince you of using epoxy. I’m providing some information for future users of epoxy.

My final thought:
If you are just in the typical wood game like most people on the WW, Most are not aware of the extremes to which epoxy has been pushed.

Super extreme: Sailboats and some powerboats use a decking system popularised by the guys at West System 40 years ago(1980). Historically decks were finished in strip teak that was screwed down in a thousand places and wide joints were filled with black poly caulk. In the last 20 years it had become industry standard on the best custom yachts in the world to have a modern method. They layup large sections of the deck on a flat table. 1/4” x 2 1/4” strips of teak with seams filled with black epoxy. After curing they bond the entire piece with a vacuum bag to the deck.

We are talking carbon/glass/foam deck with teak bonded to it with only thickened epoxy. The teak gets soaking wet, bakes in the sun and doesn’t get damaged.

Modern boat builders are known for pushing the limits and testing. Woodworkers not so much.

10/1/20       #18: Stave core door glue for 3/16" ...
David R Sochar Member

We use epoxy because it removes glue from the list of things that can go wrong.

BTW, we have measured as high as 210 degrees on the face of a dark finished door. The door was facing due East, and the rising sun was hitting it almost perpendicular.

I have seen TBIII fail 1-1/2" deep on a 1-3/4"thick panel.


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