7.1 Temporary/minor repairs
7.2 Major repairs
7.3 Joints in hull or deck
A temporary repair is usually carried out when a major repair cannot be done straight away for reasons of lack of materials and perhaps damage has occurred at sea.
Usually damage sustained to the ferrocement will be where the mortar has been shattered but is still retained by the reinforcement, so that water may be passing through the damaged area.
A repair kit should always be carried on board the boat which consists of a pointed trowel, a pair of rubber gloves, a piece of thin plywood and a litre of quick setting solution which can be mixed with some fresh Portland cement which should be kept hermetically sealed in a container.
By mixing the cement directly with the quick setting liquid to a golf ball size for each mix, it can be applied on a build up basis to the damaged area whether or not the damaged area is above or below the water line. The mixture will adhere to the inside surface of the ferrocement if hand pressure is applied to the mixture for approximately three minutes.
A minor or superficial repair usually will be a hair-line crack or surface impact damage. This repair can be effected by grinding the crack into a shallow 'V' and filling with an epoxy filler which, after setting, can be sanded and painted. Or by removing the damaged mortar in way of the impact and by using a suitable epoxy adhesive, replastering with fresh mortar.
Unsightly rust stains may be experienced through minor damage, or more commonly from mesh and in particular the tops of staples being too close to the surface of the mortar.
This type of problem is caused by lack of inspection during the casting period, and checking the reinforcement over prior to casting. It can only be overcome by tedious inspection and grinding, taking care not to damage the offending steelwork to any degree, subsequently filling with an epoxy filler and repainting as required.
Leaks which may be found on water testing the hull will usually be caused by poor penetration and inspection of the mortar in the reinforcement whilst casting.
The leak will, most likely, appear as a pin hole on the outside surface of the hull. After the hull has been fully checked over and the water removed, the pin hole can be examined using a nail to establish the route of the leak and extent of the void present. There is no need to use excessive treatment in examining the suspected void areas as this will only cause unnecessary damage to the mesh in the area.
The holes can normally be filled using a quick drying agent with fresh Portland cement or waiting for the hull to dry and using a resin based filler to effect the repair.
If there are repairs to be carried out, it will be necessary to water test the hull again on satisfactory completion of the repair.
A major repair will be necessary where the mortar is severely damaged and the reinforcement is either sheered or bent out of shape.
The loose mortar must be removed back to where the mortar is sound. By using a lump hammer against the mortar on the inside and another hammer on the outside, the loose mortar can be pulverised so that the staples in the mesh are visible. The staples can then be cut and the outside mesh slit to allow the loose mortar to be released. The outside three layers of mesh are cut back into overlaps around the damaged area so that the inside mesh and rods can be carefully cleared of any loose mortar remaining and the inside mesh remains undamaged.
Any distorted or sheared rods may be cut out and new rods wired or welded into place. Three layers of mesh are then cut to suit the size of repair and overlapped to the existing mesh left protruding from around the damaged area. All the mesh is through stapled and tidied up.
The edge of the old ferrocement is painted with a suitable epoxy adhesive for joining mature mortar to fresh mortar. The damaged area is then plastered as required.
Suitable curing will need to be carried out following the plastering operation. This can be achieved for below water line damage by relaunching after 48 hours and keeping the area immersed, and covered in wet hessian cloth on the inside of the hull. For other areas a suitable curing membrane may need to be used to enable the vessel to be put back into service as soon as possible. The longer the period of curing carried out the better.
Joints may be required for two main reasons:
1. Because the hull or deck to be cast is too large to cast in one session.Joints are usually prepared transversely across the hull or deck by wire, tying a suitable diameter rod to the reinforcement approximately 50 mm to one side of a frame, preferably a bulkhead frame, on the side of the hull being cast so that a scarf like joint is made. Thus the interior mortar is taken up and around the bulkhead frame rod.
2. There are not enough workers available to carry out the casting in one operation.
The joint is coated just prior to the start of the next session of casting with either a cement grout PVA glue or, preferably an epoxy glue suitable for connecting hardened mortar to fresh mortar, and the casting is then proceeded with on a subsequent day.