Why the Surface Decides the Bond

Every laminate is only as good as the interface beneath it. Resin doesn't bond by optimism — it wets out a surface, flows into the scratches and pores you've cut into it, then cures hard against that profile. Anything trapped in between becomes a deliberate weak point, waiting for a peel load or a damp afternoon to find it. Three offenders ruin more layups than any others: dust from sanding or a grubby workshop, grease from fingerprints, release agent, polish or hand cream, and moisture from condensation or a cold substrate. Deal with all three, in the right order, and your laminate will behave the way you designed it to.

Clean the Workshop and Yourself First

Before you touch the substrate, sort the environment. A bench that's just seen woodworking or metal grinding is full of airborne dust that will settle on a freshly degreased panel within minutes. Lay out everything you need before you start: abrasives, clean lint-free cloths, solvent, tack cloth and masking tape.

• Wear nitrile gloves and change them the moment they feel tacky or contaminated. Latex can leave residue behind.
• Keep silicone-based polishes, spray lubricants and release agents out of the room entirely — silicone migrates as a vapour and one contaminated cloth can spoil weeks of work.
• Cover prepared panels with clean polythene if you need to break off. Dust settles fast, and so does workshop humidity.
• Vacuum or brush down the bench, not the workpiece, before you begin.

Sanding: Cut a Key, Don't Polish

Sanding exists to create a mechanical key and increase surface area. Choose your grit for the job rather than grabbing whatever's nearest:

• 80–120 grit for cured laminate, metal or a heavy key on a repair.
• 180–240 grit where you want to keep a fair finish, such as prepping gelcoat before bonding.
• 400–600 grit for wet-sanding and feathering edges so fabric drapes without bridging.

Use aluminium oxide paper for dry work and silicon carbide for wet. Work in a consistent direction, change direction between grits so you can see what you've actually cut, and abrade until the surface is uniformly dull. Shiny patches mean you've missed a spot. Feather the edges of a repair and radius sharp corners, because a crisp corner will lift fabric and trap air. Don't overdo it: cutting through gelcoat or into structural fibres creates more problems than it solves. Once you've finished, remove the bulk of the swarf with a vacuum or soft brush, and blow dust out of corners and blind holes.

Degreasing Without Recontaminating

Now the grease. Acetone is the workshop standard for epoxy and polyester; isopropyl alcohol at 99% is a gentler final wipe. Avoid white spirit, turpentine and generic thinners — they leave an oily film behind that you'll never fully remove.

Use the two-cloth method. Soak one clean, lint-free cloth, wipe a section in one direction, then immediately wipe it dry with a second cloth before the solvent flashes. Fold cloths into pads and turn to a fresh face with every pass, so you're lifting contamination rather than smearing it around. Never dunk a used cloth back into the solvent tin — pour a small amount into a clean container and bin it afterwards. Work from the top down, paying attention to edges, corners and recesses where residues collect.

Then let the solvent flash off completely. Acetone evaporates quickly, but give it a few minutes and don't lay fabric onto a panel that still smells of it. Trapped solvent under resin is a bond killer, and it will show up as a blister months later.

Tack Cloth, Amine Blush and Moisture

A tack cloth — the wax-impregnated gauze sold for the job — lifts the fine dust that wiping leaves behind. Use light, single-direction passes, refold regularly and don't scrub at the surface. You're lifting particles, not transferring wax.

Moisture is the quiet one. As a rule, your substrate should be at least 3°C above the dew point; a cold panel on a warm, damp morning will carry an invisible film of condensation that no amount of acetone will fix. Bring the workpiece into the workshop the night before, or warm it gently with a heat gun on a low setting, and let it equalise to room temperature before you start.

If you're bonding to cured epoxy, look for amine blush — a waxy, slightly greasy film that forms on the surface as it cures. Wash it off with warm water and a scouring pad, rinse, dry, then sand and degrease as normal. Skipping this step is a classic cause of delamination between coats. Finally, check the panel under a good light at a shallow angle. Any dull patch, smear or fingerprint shows up at that angle and nowhere else.

Timing: Prep Before You Mix

Once a surface is clean, it stays clean for a surprisingly short time. Fingerprints, airborne dust and condensation all return within the hour, so aim to lay up as soon as the prep is done.

That's why the order matters: sand, degrease, tack, then mix. Never mix resin first and prep afterwards — you'll be working against the pot life clock with a panel that isn't ready, and the temptation to rush the final wipe is exactly how contamination gets in. Have your fabric cut, your peel ply and breather laid out, and your gloves on before the hardener goes anywhere near the resin.

If you get interrupted and the panel sits for more than a couple of hours, or overnight, treat it as unprepared. Re-tack it, re-wipe it with solvent and let it flash off before you continue. Two minutes of repeat prep is cheap insurance against a delaminated part that has to be scrapped.