Hand Lamination vs. Vacuum Infusion: Does It Actually Matter?
A question that comes up often enough to deserve a proper answer: would the structural outcome of a composite part actually change if it was hand laminated instead of vacuum bagged or infused? The honest answer depends entirely on whether the part has a core or not.
Cored Parts: The Skin Barely Matters
On a cored part — foam, wood, or Nomex core with a fibreglass or carbon skin either side — the skin’s thickness is largely insignificant to the part’s overall stiffness. The core is what provides the thickness that actually drives stiffness; the skin is a comparatively small, thin component wrapped around it. That means whether that skin gets vacuum bagged or hand laminated barely changes the part’s stiffness at all.
What it does change is weight. This is why vacuum bagging gets used on cored parts specifically: it reduces resin content and cuts overall panel weight, without giving anything up structurally. For cored parts, infusion and vacuum bagging are a weight decision, not a strength decision.
Monolithic Parts: Where the Method Genuinely Matters
Take the core away — a monolithic part, solid fibre and resin with nothing in the middle — and the calculation changes completely, because now the skin thickness is the part’s thickness, and thickness is what drives stiffness.
Here’s the mechanism, worth walking through properly: take 1,000g of fibre, vacuum bag it, and it typically comes out to roughly 1mm thick, depending on the material and weave (there’s real variation here, but that’s a workable rule of thumb). Hand laminate that same 1,000g of fibre, and it usually ends up around 25% thicker — closer to 1.25mm. Use something like chopped strand mat instead of a woven cloth, and it can end up 50–100% thicker still, potentially 2mm for the same fibre weight.
That extra thickness in the hand-laminated version comes from extra resin, not extra fibre — and because stiffness scales strongly with thickness, the hand-laminated part actually ends up stiffer for the same fibre weight. But — and this is the important caveat — it isn’t stronger. Strength comes from fibre content, and the hand-laminated version has the same amount of fibre spread through more resin, meaning a lower fibre-to-resin ratio. Stiffer, yes. Stronger, no.
Why We Infuse: It’s a Weight Decision
The honest reason for infusing parts here is squarely about weight. Reducing resin content by up to 50% compared to hand lamination adds up fast across an entire refit — potentially around 100kg of dead resin weight that simply doesn’t need to be carried around on the boat once every part is accounted for.
There’s a visible marker of getting infusion genuinely right: a laminate with a low enough resin content that it’s essentially transparent. A 1,200g E-glass panel that you can read pencil writing straight through, on the foam underneath, is a laminate with almost no excess resin in it — a result that isn’t achievable by hand lamination, full stop. Comparing a hand-laminated version of the same part against an infused one showed only a roughly 25g difference on an 800g part — which sounds small, but is a meaningful proportion of the total weight, and it’s a difference that compounds across dozens of parts on a full interior refit.
Getting to that point took solving an equipment problem first: the original plywood infusion table wasn’t consistent enough, and switching to a non-porous table made the real difference — full vacuum, zero leaks, and resin wastage that’s now roughly on par with hand lamination rather than considerably worse.
Materials Sourcing: A Genuine Find
Worth a mention for anyone infusing parts in Europe: Easy Composites, generally known as a UK-based supplier, also has an outpost within the EU — meaning Brexit-related friction isn’t the obstacle it might seem for anyone sourcing from Spain or elsewhere in Europe. Their Fusion FX spray adhesive is worth calling out specifically — it melts directly into the resin during infusion and is sticky enough that far less of it is needed compared to a standard 3M spray adhesive. Vinyl ester infusion resin, glass bubbles, fumed silica, E-glass fabric, and transfer medium have all been sourced through them too, at noticeably better pricing than previous suppliers — a genuine quality-of-life improvement for anyone doing this kind of work regularly.
Meanwhile: Replacing the Fuel Tanks
A separate but parallel project this week: building a new shelf for a replacement fuel tank. The old stainless steel tank is 30-plus years old and showing real pitting and corrosion — diesel has started weeping through pinholes in places, which means it no longer reliably holds fuel the way it should.
There’s a genuine safety and compliance angle here too, not just an aging-material one. The old tank used a clamp arrangement sitting below the diesel’s fill level — a design that’s no longer considered compliant under ISO and related regulations, since a clamp failure in that position could spill diesel rather than contain it. The new plastic tank sidesteps that problem entirely, and comes with a real practical bonus: since it’s translucent, the whole tank effectively acts as its own sight glass, showing the fuel level directly without relying on an electronic sensor — the kind of simple, visual mechanism that tends to keep working long after sensors have started failing. A sensor’s still going into it as well, for convenience, but the visual backup is the part worth having regardless.
The new tank is being repositioned along the side of the locker rather than where the old one sat, freeing up more usable space, and sitting on a purpose-built level shelf. As with the rest of the interior refit, eliminating bulkhead penetrations is part of the plan here too — several old bolt holes tied to the fuel tank and upcoming water tank changes are being closed up for good as this work progresses. The switch from stainless to plastic also lines up with the broader weight-reduction goal, with a confirmed weight saving on the tank swap itself. The custom lid built for this same tank is covered in its own post — see Portside Upgrades and Our Epic Diesel Tank Lid.
Follow the rest of Paikea’s interior transformation on the Paikea’s Refit page, or explore more composite technique breakdowns on the Boat Building & Composites Hub. For the resin-chemistry side of this same infusion-vs-hand-lamination question, see Infusion Resin vs. Hand Lamination Resin: Why They’re Chemically Different.