Building an Acrylic Aquarium
by Brad Newton (aka FeatherfinFan)

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Solvent seaming:

Now, letís address the issue of solvent seaming. Itís a bit tricky, but once you get the hang of it itís a very efficient and strong way to bond all but the very largest of aquaria. In fact, solvent seaming is used for acrylic as thick as 1.5" in the industry!

The basics of solvent seaming are this:

  • The solvent needs to be applied on a horizontal plane to insure proper flow of the thin solvent into the seam.
  • The solvent actually pulls into the seam through capillary action and will melt or weld the pieces of plastic together, the solvent evaporates leaving a very strong and clear seam, if performed properly.
  • The edges and the space between the pieces to be bonded need to be very even. If the edges are poorly prepped or the gap between pieces isnít consistant youíll end up with a lot of bubbles and gaps, not at all acceptable for a water tight fixture.

The following tools are needed for solvent seaming:

  • A can of WeldOn 4
  • A solvent bottle with needle
  • A tube of WeldOn 16
I donít recommend using the WO16; itís not very strong and is hard to apply without making a mess. Also, I prefer using a plastic syringe with a 25 gauge needle. Theyíre very cheap at a vet supply and I usually get about 4 syringes and 8 needles at a time (< $5 US). Theyíre easier for me to control and also easier to extract the WeldOn4 from the can. Youíll see me using the syringes for this article.

I use the "pins method" for seaming my tanks, itís a great way to get flawless seams, and with some practice you should get good results. The "pins" method is as follows:

  1. You insert pins between the panels to be seamed at even intervals, this keeps a fairly even gap between your two pieces, very important for good joints.
  2. The gap needs to be large enough to allow good solvent flow but not too large as to cause the solvent to flow out of the joint and create wasteful & harmful puddling.
  3. I use ball head pins from WalMart size 17 - 1 1/16", they work well for this application.
  4. You may also need to add shims under the lower acrylic piece to keep all the pins snugged up, this insures the gap is even. VERY IMPORTANT!!!
  5. The pins keep a gap to allow a good amount of solvent into the joint, this lets the solvent melt the acrylic, you then remove the pins from the gap and the "softened"acrylic will melt together. I know it probably sounds complex, but it really isnít with a bit of practice.
  6. You have a rather small time table to remove the pins once the solvent is applied, I like to keep it about 30 seconds. If you go too long, the solvent will have already started welding the plastic, and the pins will be hard to remove and will leave air pockets where the pins used to be.
  7. The best way to do this Iíve found, is have a helper on hand. I run the solvent, making sure to get a gap free solvent run, and after 30 seconds have gone by, the helper starts removing the pins at the same rate that Iím applying the solvent. For short seams you can do it all yourself, but itís far better in my experience to take your time on long seams and use a helper rather than trying to apply the solvent and hurry back to remove the pins. It's just too much for one person to do.
  8. I mentioned having the pieces overlap a bit. You want at least a 1/16" overhanging edge on your bottom piece for the melted puddle (fillet) of acrylic to set on, this seals in the edge keeping air out of the seam, very important for quality seams.
  9. You want to peal back or remove part of the protective paper in the area of the seam, I like to keep the paper about 1/4 - 1/2" away from the seaming area.

Hereís a pic of some pieces ready for seaming, if you notice the pins are about 6" apart, and they all fit snug so no shims are needed in this case

When you have the pins under the sheet it has a tendancy to roll on the pins, you may want a helper to hold the sheet as you apply the solvent. With practice, youíll know what your limits are. For larger sheets, Iíve designed some holding jigs as shown. Theyíre made from 1" PVC and I donít glue any pieces together, you just make the vertical piece as long as the sheet youíre trying to hold, and interchange the vertical piece as needed per piece size. The double elbows on top can turn to hold the piece tightly and it works well to keep the pieces at 90 degree angles.

When you load your solvent into your syringe or bottle, itís a good idea to turn the needle upright and expel any air in the bottle/syringe before running a seaml. This will keep bubble buildup to a minimum.

Itís best to keep your needle on the lip of the lower piece as you run your solvent and try to keep the needle ahead of the solvent. It can get clogged if youíre pushing the needle into the seam.

Try to keep your needle flowing quickly down the seam. If you have a spot that wonít fill you may have to go to the inside of the seam to get the seam filled, but good joint prep and pinning/shimming should eliminate trouble spots.

Remember to allow 30 seconds, then start removing pins. The acrylic piece may move on you; just gently move it back into place and try to keep from spreading the melted plastic around too much. Practice again is key here!

Once youíve seamed a section, let it be for 3 - 4 hours before moving it. This is VERY IMPORTANT!

Clear, bubble-free joints are what youíre striving fo., Keep practicing until your results are bubble-free, solid and clear. Itís not always possible to eliminate all bubbling, but your joints need to be solid from edge to edge. A couple pin hole bubbles here & there arenít a problem, but a cluster of bubbles or gaps could cause a failure down the road. Youíll know when your seams are right after working with acrylic for awhile.

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Disclaimer: By building this DIY project you agree not to hold the author or the owners of this Web site responsible for any injury or bodily harm you may cause to yourself or others. Always wear safety glasses when working with tools and keep chemicals and power tools away from children. Read and understand all safety instructions pertaining to equipment prior to use.           

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