It is always best practice to apply the treatments by brush and ensure that each coat is worked deep into all joints particularly at corners and between logs. Do not brush too thin or apply over thick. Ensure all faces and edges of doors and windows and their frames are also weather protected. Ensure exposed end grains of logs are thoroughly coated with three or four applications.
For the internal treatment, assuming you do not expect dampness being created in the cabin and also that you wish to retain the light pine appearance, simply apply the one coat of Cuprinol, Blackfriars or Sadolin clear wood preservative or similar all purpose preservative.
If there is likely to be moisture created within the cabin e.g. from cooking, many people breathing, gas heater, open garage doors and concrete floors, hot tubs etc., the internal faces of the walls and ceiling must also be waterproofed. You could use Sadolin Extra Durable Clear Coat or Clear Polyurethane floor varnish. In all cases it is important to treat inside faces of doors and windows with the exterior weather protector stain to prevent differential moisture absorption that can cause warping of the doors or windows.
For floors we suggest Sadolin Polyurethane floor varnish in clear or oak finish.
All treatments are to be applied in accordance with the product instructions and maintenance coats are to be applied at intervals recommended by the product supplier.
It is sometimes necessary to add a silicon sealant to some joints in the cabin. This is always needed for log end to end butt joints that occur in long walls and sometimes around door/window frames to wall joints and corner joints depending on weather conditions imposed. It is a simple case of running a bead of silicon water proof sealant into the joint to fill any gaps and provide a cover fillet.
However we recommend that the silicon is only applied after all other treatments are completed and the wood has dried and settled. For this reason our installers are not in a position to apply the final sealants and responsibility for doing this lies with the customer.