What is the best gap filler to use on blue board
Welcome to the Bunnings Workshop community @ac1977. It's fantastic to have you join us, and many thanks for your question about filling the gaps between blueboard sheets.
Are these large gaps or very fine gaps? Perhaps you might like to show us some images of what you would like to fill.
The gap between sheeting is normally set with Dunlop 3kg Fibre Cement Jointing Compound and Builders Edge 50mm x 90m Alkali Resistant Render Fibre Cement Tape in much the same way Gyprock plasterboard sheets would be. The tape is used to prevent the jointing compound from cracking. I'll include a video below which shows the process on interior Villaboard sheets as it's a similar method.
Please let me know if you have any questions.
That's a gap that should probably have been set originally with the above-mentioned products. Now, your best option might be to use a flexible and paintable polyurethane sealant like Sika 300ml White Sikaflex 11FC Plus Polyurethane Adhesive Sealant. It's a great product for joints that might expand and contract.