Hands on Experience of Bonding Heavy Laminations Using Epoxy?


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27 Oct 2022
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Just wondering if anybody has good and ideally repetitive hands on experience of this sort of work and is a position to provide some tips regarding the practicalities? All feedback appreciated.

I'm getting ready to glue up some 125 x 40mm x 2,200mm long laminations in beech to make the top for a heavy bench. Similarly in shorter lengths for legs etc.

Most use one of the usual modified PVAs and they are convenient - but I'm not terribly keen because of the risk of creep and their less than fully waterproof nature. (despite the claims...)

Thinking of using the new West G-Flex 650 flexible-ish epoxy - basically because standard epoxies while waterproof are not reliable on timber in circumstances where the wood may move due to significant changes in moisture content. They also often require filling to keep them in the joint.

Epoxy adhesives are waterproof and get a very good bond on most woods, but the wood cells adjacent to the bondline which are partially filled with it can become brittle and can fail if there is a lot of movement. Epoxies get used by home aircraft builders for example but are not certified for commercial aircraft use on timber for this reason in the US.

Epoxies are widely used in boat building, but timbers are normally sealed with a coat of the epoxy all over to avoid this risk.

The G-Flex 650 data suggests that it by virtue of being flexible avoids this problem and contact with West's tech support in the US backs this up - they publish test data which says that it holds up on a variety of woods cycled from almost fully dry to saturated with water.

The handling of the stuff is where it gets interesting. G-Flex 650 is about the thickness of honey (a bit thicker at 65 deg F) and can be filled to further thicken it if needed - but this hopefully will not be required on what will be tight and horizontally oriented joints. There's a thicker filled 655 version but this likely contains silica (?) which could be very hard on cutting tools.

It's very slippery and laminations will move about under the clamps unless located. (biscuits?) One positive is the 40-50 min pot life - although this is temperature dependent.

Too much epoxy squeeze out is expensive, a terrible (the very moderate word I first used got censored by the system - bloody hell!) to clean up and is best kept off clamps etc. - so lots of plastic sheeting and well controlled/'just right' application quantities are adviable.

Epoxies don't like temperatures much below 70 deg F so a reliably heated workshop is advisable at this time of year - they will set well below this but don't develop their full properties. They require only sufficient clamping to close the joint, too much pressure can cause dry joints. The other side of this is that there needs to be enough epoxy in the joint to ensure that the surfaces are well wetted.

It's important not to handle the stuff - to use gloves etc. The hardener can trigger skin problems and even potentially serious immune reactions etc in some.

I've lots of experience of handling epoxies in moulding and small adhesive applications, but not in this sort of scenario - and it's clearly important to figure out an effective working regime in advance. Hence this thread.

The critical steps are probably (a) to guarantee accurate alignment of the laminations (to minimise the requirement for flattening, and to result in flat side faces from which squeeze out can be wiped of with a scraper before it sets), and (b) for cost and convenience reasons to perfect a spreading technique which consistently applies just enough resin to give a good joint but no more.

Some trials on other jobs (laminating up blocks from birch ply) suggest that the West (1/8in?) finest notched spreader used at right angles puts down about 2.3ml per 25 square centimetres or a bit less. A notched spreader so far seems the best option by which to get accurate control of the coating. This is probably a bit more resin than is ideal, but tilting a notched spreader reduces/adjusts the quantity put down.

A look inside some test laminations even suggests that if using this preader it may be enough to apply the epoxy to one surface (if it is flat/planed) using the above spreader - although it is often recommended to wet both surfaces before assembly.

There's a YouTube video of a well known (I think) Australian maker laminating curved table legs (which he seemingly makes regularly) - he seems to use a spreader with no notches and is very sparing in his use of adhesive but does coat both surfaces.

Cost is a factor and it would be easy to add say 30%+ unnecessarily - so getting this right is important.

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I have done many such jobs making laminated deck beams & other components for boats.
Good prep is essential & nice clean surfaces, you can glue straight off the circular saw but sanding is good.
Always sand a tiny radius on the outer face corner of each lamination, if its a heavy bend & there is the smallest nick in the grain its liable to break at that point.
Dont make your laminations too thick for the bend, more thinner ones means less spring back when you take it off the mold.
Its often good to have a dry run, make sure the mold is strong enough & has enough places for clamps, Set as many clamps as you can so they are ready to be wound up. Nothing worse than having to unwind clamps in a hurry!
Use plenty of brown parcel tape on the mold so the epoxy dont stick to it!
When gluing up start with the bottom one & butter up with a flat stick, dont skimp as a starved glue joint is bad. Too much wastes glue! As each lamination is laid on top of the glue bang a fine brass panel pin in the middle & about a third from the end, stops them sliding about.
When the stack is assembled clamp on the mold in the middle & work outwards alternating sides as you go.
Sometimes the stack will start to twist Or some strips lift, squash them back into line with a clamp.
When done scrape off as much glue as you can.

Top tip, Make sure your mold is well supported, Last summer i had a big lamination job on a boat, kind of a half hoop chine piece for the stern of the launch im rebuilding, section was about 35mm deep & 12 3mm laminations about 8ft long. I laid the mold on my sawbench, glued up & started clamping, halfway round the weight of the clamps over balanced it & the whole lot came crashing over. It was very hot & the epoxy was starting to kick even though i had used slow hardener. Much terrible gnashing of teeth & dreadful swearing ensued as i got the mold back onto the sawbench & this time clamped it down. I got away with it but it was nearly a write off.
I was liberally covered in epoxy! Most boatbuilders will have experienced a similar balls up!
Hi Keith. I don't at least have to contend with bending laminations - although the different risk when making up a large and heavy slab is that it needs to be accurately put together as putting it over the planer is not so straightforward.

One thing that's for sure is that the stuff gets everywhere - even without disasters : ) It's definitely territory where it's critical to be well set up in advance.

A few questions if that's OK - primarily about getting the quantity of epoxy right:

You mention buttering the epoxy on with a stick. Was that a layer, or was it wiped out fairly hard?

Was it the standard West epoxy (it's quite liquid) or another e.g. gel type?

Did you use a stick for convenience, or for another reason? i.e. was there any reason why you might not have used a notched spreader? (thinking of the Australian guy I mentioned who was using just a plain straight edged spreader)

DId you coat both surfaces in each joint/lamination?

The panel pin you mention to stop slding would be a lot more convenient than messing around with biscuits etc...

Thanks for taking the trouble to reply.
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I just use a flat stick & spread the glue on thinly just the one side, I usually use West 105 resin with low density filler, sometimes add microfibres as well as it increases strength. West brand Colloidal silica is often used as a thixotropic agent (non sag) too much of this makes the glue hellish hard to sand, West brand silica is horrendously expensive, I buy Cabosil from a GRP suppliers (East coast fibreglass) & its way cheaper, Does the same job!
When its set I use an angle grinder with coarse sanding disc to remove the waste glue before planing or sanding to shape. Good mask is essential when sanding the stuff!
Thanks again Keith. It sounds as though getting good wetting in the joints is not too difficult.

West would have us coat both surfaces with neat resin, let it soak in and then layer on the filled material. I guess the type of wood and the finish and any gaps could alter the situation a lot - but that this is probably overkill given close fitting joints and as you said flat surfaces.

Fumed silica is essentially the go to filler to create thixotropy in lots of liquid products - but is very hard on tooling. Bad news in dry/loose form for the lungs as well - it's one of those dusts (like fine wood dust) that is small enough in particle size that the lungs can't really expel it potentially leading fairly quickly with heavy exposure to COPD and breathing difficulties...

Next up I think is to glue up some test pieces with progressively reducing quantities of resin applied with a notched spreader. The difficulty with minimising resin use is that everything would then need to fit tightly with no gaps - which (apart from driving sales) is probably the reason why West advise lorrying the stuff on.

My laminations will be machine planed, so hopefully that won't be a problem..
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A quick search on YouTube using 'laminating wood with epoxy' brings up a few relevant videos.

The first is in the boat building context, the second is a West instructional video using their standard resin in which predictably enough the stuff is lorried on.

The last is the Australian video mentioned above which clearly suggests that with good surfaces, close fits and a not very absorbent wood that it's possible to be quite sparing with the stuff:

I keep the consistency about that of honey or slightly thicker as long as you get some squeeze out of glue you know you have enough on there. Having the boat nearby any squeeze out can hopefully be used somewhere as filler. You soon get good at spreading the correct amount!
Ta Keith, that makes sense. Will report on how I get on with the trials in a week or so.

I guess boatbuilding tends to be a more knock about environment compared to a small workshop sitiuation - but watching the guy in the guy in the first video in action producing tilted section laminations in situ starting with a DIY tilting bandsaw shows that it's far from unsophisticated.

My system is inclined to be a bit sensitive to stuff, but I find it important not to handle especially the hardener - I don't break out in rashes or get a reaction per se but it does cause a definite itchiness and discomfort.

I wouldn't want to end up with traces of it on surfaces around the workshop so that I was picking it up on my hands....
If you are getting a reaction be careful, a lot of people use epoxy for years with no ill effects at all (myself included) But once you become sensitized to the stuff you have problems. Because epoxy doesnt fume & stink like polyester grp resin people assume its harmless but it isnt.
I got a splash of hardener on a webbing watch strap years ago & didnt really notice, a few hours later it started to burn, took the watch off & washed my wrist. The burn blistered up & took about three weeks to heal.
The watch strap got washed well in acetone & dried out. Put it back on & the burn scar flared up within minutes.
Threw the strap away! For three years every time i got epoxy on my hands that area would flare up.
Barrier cream is good, nitrile gloves. Dont bother with the latex ones they are next to useless. Good mask if sanding the stuff & extraction.
You're spot on there on the need for care with especially epoxies Keith.

I worked in adhesives R&D for some years in the 1980s developing dispensing systems and was trained up on the risks re. sensitisation to the amines used in most epoxy hardeners. I consequently take a lot of care. There were a lot of horror stories about.

The big problems seems to arise if the stuff gets into your system through a cut, blister or whatever so that it kicks off a full sensitisation reaction in the immune system.

The trouble is that even with care it's difficult to avoid miscroscopic contacts - even cured material as you suggest in the point about sanding often has traces of these compounds on the surface. This because it's next to impossible to mix accurately enough and to create conditions where every single molecule of resin reacts with every single molecule of hardener.

Epoxy polymerises via a stoichiometric reaction = x molecules of resin combine with exactly y molecules of hardener. The standard polyester resins are catalysed = the hardener induces the cure but does not become a part of the resulting ploymer.

I've found that there's a specific wood that bothers me a little too. I don't know what the species was but some sheets of actually EN 636-3 (basically WBP) ply masquerading as 'marine ply' bought last year to make bins from the local builders providers caused a feeling of discomfort/light itch every time I touched it.

It's even possible that residues from this in the shop this are the cause of the 'crawling' feeling in my hands felt this week while working with the epoxy as I was being very careful with it.

It's off topic, but what's going on over here in the builders providers etc business on plywood is horrendous (the UK seems to be the same) - every kind of junk (not even waterproof grades) is being shoved into structural work in housing such as e.g. the framing of dormers above wall plate level.

The importers have even invented a term with no meaning whatsoever in terms of standards - they sell EN 636-3 as 'construction marine ply' which at best is perhaps depending on the species the old WBP. The providers of course label it as marine ply and sell it at a premium. All the building contractors care about is cost, they are happy to proceed accordingly...
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Worth looking at the HSE Toxic woods list, its online & lists just about every timber & what it can do to people.
Commonly used in plywood are Birch & Poplar, both can have effects on people.
One of the worst is Western red cedar, it might smell lovely but the dust from it is nasty & causes asthma & rhinitis amongst other things.
I echo your comments about plywood, most of the stuff available today is utter garbage & stuck together with what amounts to wallpaper paste.
I'm definitely OK with birch, not sure about poplar.

The plywood which I find causes a mild response has coarse grained honey coloured outer outer veneers and is probably South East Asian in origin. No idea what the wood is (the importers spec just mutters about mixed hardwoods and quotes an irrelevant CE2+ spec which has nothing to do with the ply itself - and it looks very different to their pic) in an attempt to make it sound respectable - but it's definitely a bit risky for me.

I was also this week modifying some Ikea Bekant kitchen trollies for use as assembly and infeed/outfeed tables - they are in some sport of very pale laminated hardish wood which could be poplar or maybe rubberwood.

Both are listed as irritants..
Just to say that the G Flex 650 worked nicely on the laminations.

The viscosity is about right for horizontally oriented laminations, and would probably be OK for vertical joints too provided the sufraces are both flat, pretty smooth (e.g. 80 grit sanded) and clamped to each other.

It wasn't tested that way but probably would run out of a gap. The filled/gel G Flex 655 might be better in that situation - more a boat building than a cabinet making scenario.

The finest toothing on the stock West white plastic spreader puts down more epoxy than is ideal for this sort of joint = waste and mess. I ended up using a stright edged scraper to wet one surface (wiping off almost all of the epoxy), and coated the other with the above fine tooth spreader tilted at about 45 deg.

I've experienced problems with thick bond lines with filled epoxy adhesives before, but the 650 squeezed out nicely to leave a not very obvious bond line with moderate clamping force. Heavy clamping could well dry joints out.

Test pieces saw the wood fail and not the bond.
If youve got a couple of old handsaws ( disposable ) kicking about, you can make a notched spreader to suit your purpose. Cut off a legth of sawblade, file the teeth down to within say 1mm high and give it a try.... on a general purpose disposable, thats probably 1mm gap and 3mm tooth, 1mm gap 3mm tooth etc etc?
Interesting discussion, but I would take a different route altogether and use a plyurethane glue. I believe this is widely used in glue lam applications and it is both waterproof, strong and very flexible - a film of it will very easily wrap around a pencil. I have used it myself for steam bent laminations intended to flex in use with great success. I used a Swiss one with a 60 minute open time which sadly seems no longer to be available. Most of them have a short open-time but Bison PU Max has a 30 minute open time and I have had good experience with it. Still messy but Bison is low foam and less inclined to run and spread than epoxies.

I have used a polyurethane from a local adhesives supplier on smaller jobs with success. Also the generic Gorilla Glue which performed more or less identically.

It definitely would do the job - and it avoids the need to bother with mixing and as you say is waterproof and flexible etc.

I went for the flexible epoxy this time because I was cautious about the possibility of the foaming generating enough pressure to push open the glue lines since the joints are of pretty large area. The limited shelf life of the polyurethane once opened has also meant that I have never been able to use a bottle on a second project some months later.

Regarding running - even the less viscous G Flex 650 is quite a bit thicker than the well known standard West 105.

The big advantage of the polyurethane has always been its flexibility and waterproof nature. The theory according to West is that their G Flex epoxies are flexible enough to make them suitable for use on wood which moves in response to changes in mositure content too.

They hopefully are correct...

It might well be OK on laminates which must flex too..
I went for the flexible epoxy this time because I was cautious about the possibility of the foaming generating enough pressure to push open the glue lines since the joints are of pretty large area. The limited shelf life of the polyurethane once opened has also meant that I have never been able to use a bottle on a second project some months later.
It doesn't foam if it is under pressure, so the only foam is where there is squeeze out or a void hence what some see as its gap filling advantages, although why anyone would think that filling gaps with a load of bubbles is an advantage is a mystery to me.

Polyurethanes got a bad rap in the US Jim when one manufacturer set out to push them as a generic woodworking adhesive - this seemingly as a consequence of people either not clamping it tightly enough, or probably more typically thinking that it could fill gaps.

The foam as you imply isn't much use structurally...

The problem ultimately I guess is that the devil is always in the detail - different adhesives do different things well.
I have done quite a lot of laminating and always used UF glues. Used to use cascamite until it had problems. Now use aeolite.which has a good pot life and is simple to mix and use

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