Repairing a broken paper mould

A lot of gorgeous paper was made on this mould before it broke. I undertook to return it to a useable condition and learned a few things in the process.

The bottom of the broken side with rub strips removed. The insertion of the brass brace rod may have helped cause the break.
This frame was put together to hold the mould flat and to enable a router to cut a true surface on which to glue strips of new wood.
The first layer glued and screwed with epoxy and then machined (with the router) and ready to receive the next layer.
Beginning to repair the top of the mould. The (blue) blocks were clamped in place to guide the router to protect the chain wires where they overlap the frame. Notice that the wood that has been exposed is ‘just like new’. This mould has been in and out of water for years and has no remaining finish to keep water out. Yet beneath the darkened surface the wood is perfectly sound.
The frame has been cut away to just above the rib pins. You can see that the broken part of the mould has been almost entirely replaced, leaving only the narrow part in which the rib pins are inserted.
A longer area is routed away for the final top layer which will end up flush with the original top of the mould.

The mould had problems with sides that warped outwards. Braces had been added to restrain this but weakened the mould frame, resulting in a break which made the mould unusable. I decided to repair the mould by replacing parts of the mould frame with staggered strips of new wood which would be screwed down and glued with epoxy. The first step was to rough out a long area on each side to prepare a space to add the first layer.

The mould was then clamped into a specially made temporary frame. This provided a reference surface to enable a router to machine a true surface for glueing the new wood strips to.

New braces were installed along with the first layer. These are of a different design and should be much stronger than the ones they replaced.

After two layers of wood were added to the bottom, the second longer than the first, the mould was flipped over and clamped in the frame with the wire side up to repeat the same process of cutting away old wood and adding new strips but working from the top of the mould.

Great care was taken not to let the router bit contact the laid or chain wires. The remaining parts were carefully chiseled way to leave a good surface for gluing the next strip in.

A final layer was then added to bring the ‘patch’ flush with the top of the mould. The copper edging was tacked back into place, finishing the top repair.

One more layer of wood was added to the bottom and given a rounded shape to match the remaining original parts of the mould frame.

The first cut has been roughed out freehand with a router fastened to a long base to span the sides of the mould. The little ‘pedestals’ were left to give the router a surface to ride on. They were chiseled off before machining a smooth surface with a router in the temporary frame.
Two new braces were installed along with the first layer of wood. Threads were cut on both ends of 1/8″ brass rods. Each end was then threaded into a tapped delrin block. This gives a very strong connection.
A second layer has been added to the bottom of the mould.
The router is attached to a long base that spans the width of the mould.
The first top layer glued and screwed
The broken side of the mould showing the repair. One more layer will be added to the bottom to finish the repair.
Gluing on the last strip on one side of the mould.

What I learned.

The sight of the ‘like new’ wood that was exposed during the repairs reinforced my suspicions that any kind of finish which attempts to ‘protect’ a paper mould from water is most likely pointless. I think if the wood is allowed to dry thoroughly between uses the mould will be fine. I think wet wood (wood is ‘hydrophilic’) allows water to flow better (along the surfaces of the mould while sheet forming) than wood that has been covered with a water resistant (‘hydrophobic’) coating.

Preparing and testing wood before using it is important to prevent the mould from distorting when wet. Unproven wood can lead to multiple problems due to warping; deckles that don’t fit well, difficulty couching, and uneven stresses on parts of the mould which can shorten its life.

Questions

Rub strips made of boxwood or hornbeam (I can’t tell the difference) are nailed to the bottom edges to protect the mould from wear. On this mould (and others I’ve seen) these are attached in short sections that have gaps between them. The gaps seem intentional and it’s hard to see what purpose they serve. You can see here that a single piece of wood was nailed in place (the grain is continuous) and THEN sawn in two! The saw cut goes down into the mahogany frame. Was this to keep the strong, hard, possibly ‘ornery’ boxwood from distorting the frame? There may be another reason but I can’t think what it would be. The nails used to attach it are ring shank nails; possibly bronze boat nails.

Note

This my very first blog post. The choice may seem arbitrary and, in fact, it was! I hope to share a lot of stuff I’ve learned over the years but the order of topics will likely follow no discernible pattern. I hope some of these posts will be interesting to you.

3 thoughts on “Repairing a broken paper mould

  1. more introduction to the project…age and size…agenda for repair…i.e. reconstruction or restoration. Did the repaired mold go back into use?

    Like

  2. Hi Tim!

    To quickly answer your question on the boxwood…

    The first reason why boxwood is added on the bottom of the mould is to protect the mahogany. Large moulds are heavier, and when handling those around the vat, they are more prompt to be damaged. Mahogany is very good for moulds, but it doesn’t take shocks very good. Having a strip of hard wood on the base will offer a good protection against everyday handling.

    As you know, large moulds are slightly curved to compensate the weight when pulling them out of the slurry in the vat. The mould will bend, in the opposite direction, and be flat during the process.
    In order to allow the mould to bend, and be “flexible”, the boxwood is cut, most of the time only once in the middle of the long side. If the boxwood isn’t cut, it will actually rigidify the mould en prevent it from bending. This simple cut in the middle makes it possible. I have seen some very large moulds with more then one cut.

    One single piece of boxwood is first glued to the mahogany, before assembling the mould. Each end of the boxwood is nailed to the frame with a bronze “grip fast” nail (boat type you are right). This is to prevent it from falling down if the glue is failing with time. The cut is made once the mould frame is assembled. The cut should only be through the boxwood, and stopped before reaching the mahogany.

    I will make some pictures next time I will do it, to show you the process in details!

    Best,

    Serge

    PS 1: Great website!
    PS 2: Good job on fixing the mould!
    PS 3: You are right about the need of adding a finish. When I asked Ron Mcdonald wish type of finish he was using, he told me boiled linseed oil, but just to make them look good. No protection needed.

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