Joined: July 2004
||Posted: 07 Sep. 2019,21:43
Terracotta, the genuine stuff, not ersatz terracotta that's really wet-cast concrete, is an incredibly thirsty material, so when it's jointed with any slurry mortar, whether cement or resin, there's a huge risk of the binder being absorbed into the body of the paving and forming a permanent stain.
The key to success would be to abso-bloody-lutely saturate the terracotta with clean water before placing the slurry, and then use plenty of additional water to keep it moving about, and to wash off the surplus. I've seen this work well with cement slurries and with 2-part resin slurries, as long as the jointing is undertaken thoroughly and speedily.
Sadly, I've seen staining problems with 1-part, oil-doped resin mortars (polymerics) where the oil gets gobbled up by the terracotta no matter how much water is applied, and it can take a season or longer for the effect to weather out.
Gun jointing is a good alternative, if your back can take the strain, but I'd look to use a purpose-made gun mortar rather than attempt to knock-up something ad hoc.
Pre-treating the terracotta with a suitable sealant (or similar) can often help minimise problems with absorption. I personally don't like the "varnished look" that comes with most sealants, so I'd opt for an 'invisible' treatment, that provides the benefits of reduced absorption and some stain protection without altering the appearance of the paving.
Site Agent - Pavingexpert