Asphyx Posted July 19, 2011 Report Share Posted July 19, 2011 Ok so I have got myself into a bit of a bind... but first some background. I am building a custom 2m long x 0.5m wide x 0.7m deep aquarium. It uses 21mm marine grade plywood for the shell with a glass front. The ends, bottom, rear and lid are plywood screwed and glued together and the front is float glass. The interior plywood surfaces are lined with 3mm acrylic for water proofing. This has been an extremely economic way of building such a big tank and I am very pleased with the result. Before properly researching the subject I just assumed that ordinary glass aquarium sealant would do the trick - but apparaently not. I sealed the corners using a pretty generous fillet of Selleys Glass silicon sealant for windows and aquariums. I let this cure for 7 days and put the tank in my garage to test fill this last weekend. I filled it very slowly over several hours and then watched and waited. All appeared to be fine until several hours later when it started to leak - a lot! I quickly emptied it to prevent flooding my garage so no harm done but thats not quite the result I was hoping for. So today after having done some simple research I have learnt that silicon sealant is not suitable for sealing acrylic as it will not adhere long term to plastics that exude oil (like acrylic). There is a very good explanation here: http://www.aquarium-pond-answers.com/2007/03/aquarium-silicone.html The issue is what to do now? As I see it my options are as follows: 1. I know that I can use acrylic glue to chemically bond the acrylic junctions but I don't entirely trust that this will be comepletely water tight and this will not resolve the front glass to acrylic joins. 2. I could replace the acrylic liner with thin glass but this defeats the purpose of using free acrylic and the glass against a plywood substrate that flexes a bit is likely to break. 3. Find a sealant that is: a) Safe for fish b) Able to be permanently immersed in water c) Suitable for bonding acrylic plastic (and glass) Because the plywood provides the structural support the sealant does not have to have the same strength as you might normally require, so presumably this opens up a lot more selant options. My only real option is 3 and there must be something out there. Does anyone know of a suitbale product please? I have come across Dow Corning Marine Sealant (from the web site above) but I am yet to figure out if this is safe for fish and available in NZ. Appreciate any help you can offer. Thanks. Quote Link to comment Share on other sites More sharing options...
hovmoller Posted July 19, 2011 Report Share Posted July 19, 2011 Have a look at this site: http://www.melevsreef.com/tools.html This guy is an acrylic guru! And good luck Quote Link to comment Share on other sites More sharing options...
ryanjury Posted July 19, 2011 Report Share Posted July 19, 2011 I am not sure exactly, but I am pretty sure that usually when you make a plywood tank you just seal the plywood and then I would assume you could use standard aquarium silicone to seal the glass in.. Quote Link to comment Share on other sites More sharing options...
myfishybuisness Posted July 19, 2011 Report Share Posted July 19, 2011 I am not sure exactly, but I am pretty sure that usually when you make a plywood tank you just seal the plywood and then I would assume you could use standard aquarium silicone to seal the glass in.. i think thats how most people do it :smln: have a look at this : Quote Link to comment Share on other sites More sharing options...
Asphyx Posted July 19, 2011 Author Report Share Posted July 19, 2011 Thanks. Yes I thought I would be clever and rather than find a sealant for the plywood I had access to free acrylic so thought that would be just as easy! I guess if all else fails I can rip out the acrylic liner and seal it. On that note does anyone know of a suitable sealer? I have come across a Sika product suitable for potable water (I forget the name right now) but it was quite expensive. Quote Link to comment Share on other sites More sharing options...
Squirt Posted July 19, 2011 Report Share Posted July 19, 2011 What about a black pondliner? Quote Link to comment Share on other sites More sharing options...
myfishybuisness Posted July 19, 2011 Report Share Posted July 19, 2011 What about a black pondliner? yeah i saw a huge ply tank done with that on youtube ,it lookd awsome :thup: !drool: Quote Link to comment Share on other sites More sharing options...
livebearer_breeder Posted July 19, 2011 Report Share Posted July 19, 2011 It looks like he used white bathroom sealant on all the joints and then fibre glassed the WHOLE thing inside and out. Its a fantastic idea and i have a trade account at bunnings, hehehehehehe just wondering how they painted the inside black safley? Quote Link to comment Share on other sites More sharing options...
Ira Posted July 20, 2011 Report Share Posted July 20, 2011 just wondering how they painted the inside black safley? Paintbrush or roller and lots of ventilation would be my guess. Black pond paint probably. Quote Link to comment Share on other sites More sharing options...
the-obstacle Posted July 20, 2011 Report Share Posted July 20, 2011 I'd go with a pond liner for that size. Quote Link to comment Share on other sites More sharing options...
David R Posted July 20, 2011 Report Share Posted July 20, 2011 I used the IPS WeldOn #16 for making the acrylic drip tray in my sump, its available from Mulfords Plastics in Auckland (http://www.mulfordinternational.com/Home.htm), not sure where you'd get it from in Hamilton. They would probably be able to advise you on something to use for acrylic to glass joins. Alternately, you could replace the glass window with acrylic. I wouldn't go with pond liner for this kind of tank, there are many better ways of sealing it (such as fibreglass/epoxy). Have a browse through the DIY Tanks forum on monsterfishkeepers.com there are hundreds of threads on large ply tanks with viewing windows, and many knowledgeable people with first-hand experience on the subject. The only downside is [being a mostly-US based forum] they often use products unavailable here or branded differently. Quote Link to comment Share on other sites More sharing options...
Asphyx Posted July 25, 2011 Author Report Share Posted July 25, 2011 Okay, so after much research on the interweb and talking to various reps and specialists I have come to the conclusion that there are very few, if any products available that; 1. Is non-toxic. 2. Is permanently immersible. 3. Will seal/stick to/bond acrylic. I have even spoken to specialists who have recommend products and then when I check the product data sheets these blatantly state that these should not be used for one or more of these applications. There is endless (and mostly poor) advice on forums and even products that many swear they have been using for years fail when you check the product data sheets. I had all but given up until today when by pure chance I came across Gold Label Pond Aquarium Sealer. http://www.huntsupplies.com.au/goldlabelsealer.html The product data sheet specifically states it is ok for acrylic. If I can get some in from Australia (I can't find anyone who sells it in NZ) I will give it a go and let you know. Has anyone come across or used it? Quote Link to comment Share on other sites More sharing options...
Squirt Posted July 25, 2011 Report Share Posted July 25, 2011 Huh that's really weird. You hear about acrylic tanks being made all the time, but there's nothing aquarium suitable? I'd love to hear how it goes. Good luck Matt Quote Link to comment Share on other sites More sharing options...
Asphyx Posted July 25, 2011 Author Report Share Posted July 25, 2011 Yeah its because most ordinary acrylic tanks are glued/chemicaly bonded whereas in my situation I just want to seal it. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 26, 2011 Report Share Posted July 26, 2011 Years ago I built a 3m tank which was firbreglass over plywood in a steel frame. The tank was 3100mm x 1200mm x 1000mm with a 950mm front window. The ply was standard building grade, 2 x 19mm laminated for the required strength. This was then covered with 3 layers of chopstrand mat and polyester resin to provide the final strength and to seal the wood. The inside was painted with matt black gel-coat. Where the gel-coat met the silicone for the front glass a special primer was used to allow the silicone to bond properly. The primer and silicone came from Ramset. The tank is still in use today at the National Aquarium. Points to consider when sealing a wooden tank. - The corner joins are under extreme forces. Any movement will cause cracking if the wrong sealing technique is used. Paint is no good. - A chamfer or cove will reduce the risk of cracking - Rubberised paint may work if it's thick and flexible enough. You may be able to get a primer to paint onto the acrylic to allow silicone to stick. Quote Link to comment Share on other sites More sharing options...
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