The fin box is the fitting that holds the fin. Some replacements change the whole outer part; others attach to a plate that stays inside the board. Identify which type you have before cutting.
Do not mix parts, cleaners, pressures or waiting times from different systems. The replacement must match the shape, base and fin type.
Stop before cutting or bonding if any of these cases applies:
Compare shape, measurements, fittings and replacement instructions. Find out whether you must replace the whole outer part or attach the new box to a plate that stays inside the SUP.
Do not buy by visual similarity. Dimensions, base, finish and adhesive compatibility must belong to the same system.
Follow the replacement manual. Some systems require a deflated board; others require a precise pressure. Do not choose a pressure by imitation.
If the manufacturer requires a deflated board or another pressure, its instruction prevails. Secure the SUP without loading the damaged area.
Use only the method stated for your replacement. If the whole outer assembly is replaced, lift it as described in the manual. If the plate must remain inside the board, keep the blade almost flat and make shallow cuts around the broken box.
Before warming, close and remove every solvent and wait until the vapours have gone. Always point the blade away from your body and the air chamber. Stop if you cannot control the shape and depth of the cut or identify the system.
After removing the part, check that the skin is not cut, distorted or separated from the layers below. When the plate stays inside the board, it must be firmly attached, flat and free from cracks.
A moving plate or damage beneath the box changes the repair. Do not conceal it beneath the new component.
Remove loose adhesive without thinning the support. Then sand and clean as stated by the kit. Protect graphics and allow every solvent to evaporate fully.
The two replacement types may require different preparation. Use only the sandpaper, cleaner and heat stated in your kit manual.
Try the replacement without adhesive. For a complete assembly, check that it sits flat. When keeping the inner plate, try the box and patch together, identify the bonding side and align the fin slot with the centre of the board.
The box and patch must not rock, force the plate or require improvised filler. Stop if the textured side or axis is uncertain.
Spread adhesive only on the surfaces stated by the kit. Make thin, even layers and join the parts when the label says they are ready. Do not mix instructions from different systems.
The number of coats, waiting time, temperature and use of heat depend on the adhesive. Follow the label on the product you are using.
Follow the marks and keep the box aligned. Lower the complete assembly a little at a time or centre the patch on the plate, depending on the replacement type. Press from the centre to the edge and use weights or clamps only when the kit requires them.
Never use heat near open solvents. If the system requires heat, close and remove everything and ventilate until vapours have completely dispersed before warming.
Keep the replacement still for the full time stated in the instructions. Then inflate little by little, inspect the edge and fit the fin without forcing it.
When the adhesive is fully dry, inflate little by little to the pressure stated for the board. Check the edge and alignment, then fit the fin without force. Movement, bubbles or air loss require assistance.
Confirm the material, prepare a patch and apply two-part adhesive without skipping waiting times, pressure or final checks.
Locate the leak with soapy water, try the least invasive correction and replace the valve only when it is genuinely required.
Seven illustrated procedures, from diagnosis to the condition that says stop.
Send RiparoSUP photographs of the box, exposed area and replacement before cutting further or applying an unverified adhesive.