The next stage in the process is to caulk the deck. Before any sealant, the seams need to be filled with caulking cotton. This is to block up the cracks before the sikaflex is laid on top. Being a natural material with some give, it allows the deck to expand and contract, adds some insulation, and narrows the gaps meaning you don’t have to pour tube after tube of sikaflex into the seam (or indeed straight through into the hull creating stalactites or stalagmites of black grunge!).

Timing is everything, the caulking cotton can’t be wet so the seams have to be raked and the wood dry. There isn’t a cats chance in hell that you can do the whole deck in one hour, so you have to start at the highest point and sikaflex as you go to seal the cotton. This means it is all tapes and primed before the cotton goes in and the weather has to be sunny. 

The process has been divined through a bit of experience, lots of reading and some trial and error. Truth be told, for every person you consult, you get at least three differtimes t opinions…. To prime, or not bother? Mask or rely on a steady hand? Pump the sikaflex in, or spread it down it down into the seam? While there are some basics rules, a lot of the finer points of technique seem to come down to how you work best.

    
The caulking cotton bit is less subject to debate. The cotton comes rolled as eight strands. These are looped back on themselves and pushed into the seam. Once you have around six inches, they are tapped with the caulking iron and hammer into place. Using a rocking motion with the iron and working up the seam. Finally the whole lot is pounded into place with a further v-shaped iron to check it is truly in place. If the seam is particularly deep or side, add more cotton. 

Pretty time consuming but, truth be told, not an unpleasant job if you have a knee cushion and a good podcast.

In the picture below, the cotton to the left has had its final hammering.