"Seamless" has three meanings in stone work. Acrylic solid surface can be genuinely seamless (thermoformed, with joints polished invisible). Quartz can achieve a hairline joint visible only up close. Natural marble, granite and sintered stone always show a joint; book-matching only makes it look natural. Knowing the difference avoids disappointment after ordering.
Acrylic solid surface can be joined with colour-matched adhesive and polished, or thermoformed into an integrated basin, giving a truly seamless result. Quartz joints can be polished to a hairline but still exist. Marble, granite and sintered stone always have visible joints; book-matched layouts simply make them look more natural.
Site measure, factory cutting to drawing, routing and aligning the joint, bonding with colour-matched adhesive, curing, sanding from coarse to fine, then polishing to match the face. Temperature and humidity must be controlled and the adhesive colour matched, otherwise joints darken or yellow later.
Avoid standing water and strong acid or alkaline cleaners. Do not place heavy loads on joints or strike them with hard objects. If a joint darkens or cracks, arrange sanding and repair promptly so moisture does not reach the substrate and distort the slab.
One: believing all stone can be seamless - only acrylic solid surface can. Two: believing seamless means crack-free - thermal movement and uneven substrates still crack joints. Three: believing the finest joint is best - an overly tight joint has no tolerance and cracks more easily.
Not fully. Marble veining is discontinuous so a joint is unavoidable, but a fine joint with book-matched layout makes the seam follow the vein and look unified.
Not with correct installation. Uneven substrates, thermal movement or concentrated loads can still crack a joint, so the substrate must be flat and well supported.
Usually moisture and dirt have entered the joint. Light cases can be sanded, cleaned and re-glued; serious cases need the joint redone, with drainage and sealing checked.