Hi Banjo
The technique you intend to use is what the Americans refer to as "cope and stick". It is a technique commonly used in mass-produced kitchen and bedroom doors for foil-wrapped MDF, solid MDF and solid wood doors. The size of your door(s) is not overly big for the proposed thickness, however I'm personally unhappy about the use of this technique on solid wood doors. In MDF doors there is little or no difference in the amount of movement across the sheet as opposed to along the sheet, so for all intents and purposes the material doesn't move like solid timber. In solid wood, however, the rate of movement across the grain as opposed to along the grain is different. For this reason mortise and tenon joints and later on dowelled joints were developed, so that the glue area in the joint would be increased and that there would be additional mechanical strengthening in the joint in the event of glue bond breakdown. In general a cope and stick joint glued under controlled conditions with a D3 (exterior) grade PVA glue, such as EvoStik Resin W (blue), will survive quite well, however in environments which are subject to rapid changes in temperature and/or humidity, including bathrooms, kitchens, conservatories and spare bedrooms which are south-facing, there is an increased chance of joint failure, especially if a permeable finish such as oil is chosen. For that reason I have a preference for strengthening such joints with one or two hardwood dowels. I have a couple of examples of commercially-made solid-wood cope and stick kitchen doors where the joints have been glued without dowels or pinning and have subsequently begun to fail, so maybe I should post a piccy or two to illustrate what actually happens
Brad's comment about cramping-up the joint overnight is good advice - make sure that you have enough pressure on the joints, but don't crush them as that will starve the joint and rob it of strength. At this time of year make sure that your glue hasn't been frozen and keep the temperature up to above 5° C (preferably 10° C or warmer) as the glue will fail to set at low temperatures and you'll end up with a weak white glue joint - a phenomenon known as chalking.
As to the panel requiring an expansion gap all round, MDF or not, I'm in complete agreement with JFC. Whether or not the panel moves is only part of the equation as a solid wood frame, particularly a 2m high one will move, so leave a small gap round all four sides of the panel. If you are concerned aboout the panel rattling a few small spots of clear flrxible silicone (as used by kitchen fitters/plumbers) in the bottoms of the grooves will do wonders
Scrit
ccasion5:
