Baptistry Lids11th September 2015
We reinforce the lids with timber struts for narrower pools but for wider ones, we will used a compressed box-section tubing made of compressed fibreglass because it is lighter and stronger than the matching dimension in timber. And it is certainly lighter and a LOT cheaper than using steel or aluminium.
The added advantage of GRP is that it will not swell or warp as wood can do. And, in terms of finish, we can make them in any colour, or you can stick carpet or wood tiles directly to the lids.
There will always be some flexing in the lids when one walks on them, though usually this only becomes even noticeable once the lid gets above 1.7m long. We add more reinforcing to keep the flex to a minimum, and certainly to no more than 3mm for 200kg standing weight. It will take the weight of the choir or the band! (It is odd that when I mention this, we are always asked if we can build in a trap door…)
Lids are usually 70mm deep but for longer spans we would increase this to 100mm. Conversely, for shorter spans, thinner is possible.
When it comes to lifting them out, we usually put recessed threads in one lid and send a set of eye-bolts with the lids. This way, the eye-bolts can be screwed into the lids and provide finger-holes for the two lifters. Once the first lid is out, the rest can be slid out and lifted.