impregnated with paste and I also rub a little into the notches. Standing the board vertically against the joint I feed the ends of the pasted slips through the holes and pull tight. The board is then closed carefully onto the textblock and those ‘spacers’ glued on the back edge of the boards will ensure the right tension.
Making sure the boards and slips remain attached at the same position , holding the book in the left hand, I open the board onto a knocking-down iron clamped in the end on a laying press. With a backing hammer I hammer the holes closed. More paste is rubbed onto the tapes on the inside of the board and the fibres of the slips are splayed out to reduce any bulk.
A little more paste is applied to the slips on the inside and outside of the boards and by opening out the boards, a little more can be rubbed into the notches or grooves. Closing the boards, making sure both are correctly positioned… and parallel…by checking with a set square, the book can be pressed overnight. The book must stand up straight when finished !
Whilst in the press I have a melinex sheet inserted inside the boards to protect the textblock and a stainless steel pressing ‘tin’ up to the joint on the outside, in this way I can achieve a very flat surface to the boards. The Melinex I’ve had for years, its a thin, clear sheet about 0.6mm or 0.7mm thick and while fairly flexible, is rigid enough to protect the text. and to a degree is non-stick…..I think Shepherds sell it. Stainless steel pressing ‘tins’….? ? …not available commercially and I have to thank Noel Carruthers for those…she had a batch made up some years ago. Any thin ‘tin’ slipped inside the board will do but you might want to also slip in some release paper.
Should you have made a slight miscalculation and there is still a bit of unevenness on the surface of the board where the slips are laced in, you may consider sticking on a sheet of good quality paper, say about 120gsm. This can then be sanded down to minimise the problem. I would stick it on oversize with one edge lined up with the spine edge of the board and sand off the overlapping edges to remove the excess. No doubt though, you will have spotted the flaw in this plan….sticking on an extra layer of paper will ‘pull’ the boards outwards slightly. So when sticking it on, try gluing the board…..not the paper…with PVA or EVA not paste….and rather than rubbing down in the natural way which actually stretches the paper outwards…rub down from the edges of the board towards the centre….it might help. The boards will have become a little thicker with the addition of the paper so if this is a problem, the sanding of the uneven part could be extended over the entire board.