Drilling and waterproofing holes in plywood tanks

Chihuahua6 · 08/18/2006, 10:27 AM

The tank box is put together 90X62X70X61 X32H. It will have an external horizontal overflow across the back (70"). I am planning to drill for 3 2" bulkheads in the overflow and two holes through the back of the tank for my closed loop manifold. (I don't know what size these holes should be so suggestions are welcomed.)
The tank will be fiberglassed and then epoxy paint will be applied.
-Do I do the fiberglass and epoxy first and then drill?
-How do I seal the holes, with just epoxy?
-Do I need to drill the hole slightly larger to account for the epoxy layers, meaning if I drill the hole the size I need will adding the epoxy make them smaller?
Thanks.

eastcoaster1 · 08/18/2006, 11:59 AM

I don't know too much about plywood tanks, but I have built a few boats using plywood and epoxy. The way I've sealed up holes is to make the hole about 1/4" larger than necessary and then fill it with thickened epoxy - as if you were trying to patch the hole. Once the epoxy cures you then drill the correct sized hole in the epoxy. What you're left with is a 1/4" ring of epoxy around the edge of the hole. Since the epoxy is bonded to the plywood edge it creates a totally waterproof opening.

Probably overkill since the bulkhead should make a water tight seal, but something to consider.

bassnman11 · 08/18/2006, 11:12 PM

The bulkhead should do most of the sealing. I would glass the tank, then drill for the bulkheads. Make sure the sealing surface is flat wher the gasket goes. If necessary, create a little clearance with a drum sander. Give the inside of the hole a couple of coats of resin. Install bulkheads.

Chihuahua6 · 08/18/2006, 11:35 PM

Thanks guys.

RicksReefs · 08/19/2006, 08:21 AM

after you cut the hole, the cut area should be resined over. any water/humidity that gets into the cut will swell the wood otherwise, which can make the bulkhead useless.

08/18/2006, 10:27 AM	#1
Chihuahua6 Premium Member Join Date: Jun 2004 Location: West Hempstead, NY Posts: 2,124	Drilling and waterproofing holes in plywood tanks The tank box is put together 90X62X70X61 X32H. It will have an external horizontal overflow across the back (70"). I am planning to drill for 3 2" bulkheads in the overflow and two holes through the back of the tank for my closed loop manifold. (I don't know what size these holes should be so suggestions are welcomed.) The tank will be fiberglassed and then epoxy paint will be applied. -Do I do the fiberglass and epoxy first and then drill? -How do I seal the holes, with just epoxy? -Do I need to drill the hole slightly larger to account for the epoxy layers, meaning if I drill the hole the size I need will adding the epoxy make them smaller? Thanks. __________________ Leah Amanda Current Tank Info: First salt tank 1985, current tank 150 g acrylic

08/18/2006, 11:35 PM	#4
Chihuahua6 Premium Member Join Date: Jun 2004 Location: West Hempstead, NY Posts: 2,124	Thanks guys. __________________ Leah Amanda Current Tank Info: First salt tank 1985, current tank 150 g acrylic

08/18/2006, 11:59 AM	#2
eastcoaster1 Registered Member Join Date: Aug 2003 Location: NH Posts: 265	I don't know too much about plywood tanks, but I have built a few boats using plywood and epoxy. The way I've sealed up holes is to make the hole about 1/4" larger than necessary and then fill it with thickened epoxy - as if you were trying to patch the hole. Once the epoxy cures you then drill the correct sized hole in the epoxy. What you're left with is a 1/4" ring of epoxy around the edge of the hole. Since the epoxy is bonded to the plywood edge it creates a totally waterproof opening. Probably overkill since the bulkhead should make a water tight seal, but something to consider.

08/18/2006, 11:12 PM	#3
bassnman11 Registered Member Join Date: Jun 2005 Location: Corona Ca. Posts: 674	The bulkhead should do most of the sealing. I would glass the tank, then drill for the bulkheads. Make sure the sealing surface is flat wher the gasket goes. If necessary, create a little clearance with a drum sander. Give the inside of the hole a couple of coats of resin. Install bulkheads.

08/19/2006, 08:21 AM	#5
RicksReefs Moved On Join Date: Apr 2002 Location: In America's Dangling Junk State. Posts: 6,413	after you cut the hole, the cut area should be resined over. any water/humidity that gets into the cut will swell the wood otherwise, which can make the bulkhead useless.