Thin joint or glue mortars are widely used in Germany and were introduced into Britain by Durox in 1991, but their use to date has been limited in the housebuilding arena. Celcon launched its own version of the system in 1997 and has been actively searching out housebuilders to trial the system: the James Developments site switched over to the system in March this year and has now built out seven houses using it. The company now plans to use it exclusively on the final 85 Cranleigh brick-clad homes on the site.
There are two key elements to the system. Firstly, it uses a glue mortar, more akin to tile adhesive than a traditional sand and cement mix. The glue mortar sets hard within ten minutes and this makes it possible to work with much bigger block sizes - the second key element. The limit on block size is set by what a man can easily handle: in fact, in response to feedback from site, Celcon’s currently preferred size - 440 x 560 mm, two and a half standard blocks - is slightly smaller than the format it launched its system with initially.
Evidence from the seven houses that James Developments has completed with the new system is that blockwork is going up at least 20% quicker. Any increase in material costs has been more than offset by a decrease in labour rates. “As you can imagine, this was a contentious issue,” says Stoodley. “The market rate for traditional blocklaying is now over £6 per m2. Using these Jumbo blocks, we have agreed rates of £4.75 per m2. We’ve managed to hang onto our brickies - they are taking home the same amount and are now pretty happy with the new deal.”
The point is confirmed by Ray Lancaster who runs the brickworking gang. “At first it was a real shock to the system, a completely new way of going about blockwork and some of the guys took quite a bit of persuading. But I think by and large everyone now prefers working this way.”
Stoodley reckons that laying speeds could be further increased if the houses were designed with the larger block format in mind, so that the number of cuts could be diminished. “We’ve learned a lot thus far and I’ve been impressed. It’s important not to let the blocks get sopping wet - the glue doesn’t stick to wet blocks - so even though they arrive on site shrink wrapped, we now put them under a tarpaulin as well just to be on the safe side. And for some reason I can’t yet fully explain, using these blocks has improved the standard of the external brickwork. I think it’s because the brickies get longer uninterrupted runs.”
James Developments is the largest housing site so far to have switched over to Jumbo Thin Joint blockwork but Celcon has trials in progress with some of the plc housebuilders, one of whom has already taken the walls up from DPC to wallplate within a week. And blockmaking market leader Thermalite has just launched its own large format block which if nothing else sets a seal of approval on the new technique.
Interestingly, Thermalite will be stressing that its large format blocks can be laid either with thin joint glue mortars or with a traditional sand and cement mix.
“We are in the business of selling blocks,” says Thermalite’s director of technical services, Mike Robinson, “and we really don’t mind how people lay them. There are speed gains to be had from switching to large format blocks without thin joint mortar - not so great admittedly, but enough to justify the switch. We hope that by not forcing them to go all the way across to glue mortars in one leap that this will help builders migrate slowly.”
Source
Building Homes
