A cheap and fast patch for your lettuce raft or media bed

 When I was setting up my lettuce raft recently I wanted to try to use some 6mil poly sheet that I had left over from skinning my greenhouse. I didn't want to spend the money on the 20 mil scrim if I didn't have to. Plus with the end of the roll already in my shop I decided to try it and if it didn't work I could just roll it back up and save it for later. So of course when I started filling the raft up I found a few micro holes where the folds in the plastic were. (Notice the dark spot in the center of the sheet.)

Not one to give up easily, I noted that the 3M 5200 marine caulk that I had been using on my through hull fittings says that it works wet or dry. So I cut out a 4"x6" piece of plastic, put a quarter sized blob of caulk in the center of it, folded it over and squeezed it around until it was evenly spread. Then I just opened up the patch and put it on under the water. That caulk is very sticky, with just a little smoothing out it was down.  The patch looked like it was going to be good, so I completed the fill.  The next morning I could till that they held as the wet spots hadn't spread out on the ground cover fabric that's under the poly. 

The only down side with this material is that the caulk will harden in the tube a few days after it is opened.  It is available at Home Depot, Lowes, and West Marine in  regular caulk tube size and also in small squeeze tubes. 

I use this stuff on all my through hull fittings, tank construction and anywhere I need a strong bond in wet conditions.  Mat Roberts