The Latchform

In 1999 I saw the writing on the wall regarding my sailcloth form. After over 100 sculptures it was pretty well worn out, so I started planning a replacement. Cloth has the advantage of being portable: just roll it up and carry it away. Its disadvantage is that it requires some sort of structure to hold it up and open.

Many sand sculptors had started to use above-ground swimming pool sidwall plastic for their forms. It's self-supporting and simple to use, but I didn't like the crude way they just clamped the overlapped plastic against itself. I thought there had to be a better way.

A search on the Internet found a source for the stainless steel over-center latches I needed to make the form. Over a weekend I assembled the pieces; the next weekend I took it out for a test. Basically it worked, but it leaked too much. There were two sources of leaks: the bulge of the plastic at the seal between latches, and through the bolt holes.

I stiffened the seal area with aluminum angle bolted to the plastic. The bolt holes I sealed with silicone. Then it was time for another test, and this time it worked. This is a very good form. It holds the sand very tightly, with no stretch that would prevent good compaction. It takes about five seconds to set up and about three seconds to take off. No hassle, no wasted time. I like this form a lot.

Seal Detail

The form's end gap is flanked by aluminum strips one inch wide, bolted through the plastic. The form's other end is slightly rounded, and is pulled into the seal by the latches. There's an eighth of an inch of silicone in the gap for the free end to seal against. As long as I keep sand out of the gap it seals well, with only a slight amount of seepage.

Latch Detail: Closed

The latch's handle is to the left, with the latch rod projecting to the right. It has a ball end that engages a shaped slot in the keeper, at far right. Note the threads for adjusting the rod's reach. Once it's ajusted properly it's held in place by the jam nut.

Latch Detail: Open

Here the latch's handle is projecting straight out from the form so the rod has disengaged from the keeper. It's still in the keeper's slot, ready to be swung out and away so the form can open.