I read this a couple of decades ago.
Good gluing practice preserves the cell walls of the timber so that capillary action draws the resin into the cells for adhesion over a much greater area.
DON”T USE SANDPAPER COARSER THAN 100grit ON TIMBER TO BE GLUED (or Painted/Varnished)
Using blunt tools or sandpaper more coarse than 100 grit smashes up the cell wall structure of the timber so you are gluing to debris rather than the good wood and the advantage of the glue reaching down into the cells is lost.
Sharp tools are good for preparing wooden surfaces that are to be glued. Planes and tungsten saws. Planes and tungsten saws.
Dull cutting edges of planer or jointer knives crush and burnish the wood surface.
The crushed and burnished surface inhibits adhesive wetting and penetration. If the adhesive does not completely penetrate crushed cells to restore their original strength, a weak joint results.
Sharp sandpaper 100 grit or finer is good – epoxy construction avoids the warning about swelling and shrinking of surfaces in this case.
Abrasive planing with grit sizes from 24 to 80 causes surface
and subsurface crushing of wood cells. Figure 9–2 shows
cross sections of bondlines between undamaged, knife-planed
Douglas-fir lumber compared with surfaces damaged by
abrasive planing. Such damaged surfaces are inherently weak
and result in poor bond strength
Here is the source document
Source: Forest Products Laboratory. 1999. Wood handbook—Wood as an engineering material.
Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service,
Forest Products Laboratory. 463 p.
