Glues and bonding materials
Written by Ben
Last updated on 2008-12-06
We at SSC get a lot of questions about glue selection for repairs, modifications, and homemade water guns. In this article I want to spell out the options available, what not to do, and give some tips. This page will be a work in progress all of the time because new information about which glues work well comes in all the time.
Glues that work well
As always, there are variants of certain glues or cements that work with certain materials better. Some glues work better with plastic-to-plastic bonds than plastic-to-metal bonds as is. Some work only with plastic-to-plastic bonds of like plastics. Always check the bottle to make sure it works with whatever you are looking to bond.
Most of these glues, unless otherwise noted, are available at hardware and home improvement stores, as well as over the internet. McMaster-Carr has most of these glues.
Epoxy works well most of the time and thus is suggested most often. Generic epoxies work well, but some people prefer JB Weld brand. Epoxies are most ideal for small cracks because they can fill in the crack and go all around it.
Similarly, super glues can work well too for small cracks, but they may not be as strong as epoxies.
However, for filling in things, especially larger things, epoxies and super glues do not work very well because they do not have much volume. Epoxy putty is suggested for these purposes. Epoxy putty is ideal for filling in larger cracks, reinforcing the structure of things, attaching PVC (or most other plastic) pipes to other things, filling in spaces, and attaching things together.
Hot glue can be a good choice to bond things together. However, the majority of hot glues are not useful. Craft projects never require a seal, so the usual "low temp" hot glue sticks are inadequate. High temperature "hot melt" hot glues can bond to plastic very well. Here is a link with a bunch more information about hot melt glue sticks. Also, remember that hot melt requires a higher temperature glue gun, so be extra careful not to burn yourself. Hot melt glues should be available in craft stores and the internet.
IPS Weld On is a solvent welder for some plastics. McMaster-Carr carries it as simply weld-on. It bonds some plastics to plastics. It could be helpful when repairing water guns by putting a plastic reinforcing strip over a pressure crack and then using Weld On to both bond the plastic crack back together and the reinforcing/sealing face over that.
There are variations of all glues, so check if it bonds with the materials you want it to bond to.
When using these glues, remember that the instructions provided override any tips or suggestions provided by anyone else. Always trust the instructions the most.
Glues that don't work
Do not use PVC cement on water gun repairs. The plastic in manufactured water guns is not PVC, so PVC cement does not bond it together.
Rubber cement, silicone glue, and plumber's goop do not bond. They might seal well, but they don't bond.
Tapes of all kinds (duct, electrical, masking, Scotch, etc.) do not seal.
Where to buy
You can buy most of the glues mentioned at home improvement, hobby, hardware stores. Craft stores should have hot melt glue guns and glue. WalMart should have epoxy at the very least as well. McMaster-Carr carries the glues we've mentioned too.
Tips and helpful techniques
- You can remove excess epoxy by rubbing a paper towel with acetone on it on the epoxy. Nail polish remover works too because it is acetone. Just be aware that whatever can remove the epoxy will also remove the plastic as well.
- Always roughen up the area being glued before gluing. Use coarse sandpaper or a file to roughen it up. This cleans the area, creates more bonding spots, and allows for bonds in different directions.
- Discard old glues and epoxies. Glues and epoxies do go bad with time. They have expiration dates. Don't gamble the success of your repair on an old glue. I had one repair go bad because I used old epoxy, and I learned my lesson.
- If the instructions say mix thoroughly, mix thoroughly.
- Whatever the instructions report as the curing time, wait twice that. Be sure to READ the can/bottle, and read it correctly. There are times for safe handling, and full strength. Safe handling does not mean pressurization—full strength does. Never under any circumstance pressurize the gun before the full strength time.
- Always check to see if the epoxy has cured before testing. If it is sticky, it has not cured, so wait longer. If it stays sticky for a long time, either your epoxy is old or was mixed incorrectly.
- Make sure whatever you are curing is in a warm place unless the package recommends cold.
- Sometimes it is a good idea to apply a reinforcing strip of plastic or metal.
- Check if the glue bonds to what material you want it to. Usually what materials the glue bonds well to is reported on the glue or a website.
- Open valves to let air in during curing.
- Clamp parts down it if will help keep them together.
- Sometimes a combination of glues is helpful. The combination of epoxy over a small crack and then epoxy putty over that could be stronger than just epoxy alone if you are having trouble with that crack reopening. Apply the epoxy first and wait for it to dry, and then apply the epoxy putty.
- For the best use of epoxy, mix the two parts for at least 10 minutes. This requires you to avoid 5 minute epoxies. Mixing for at least 10 minutes ensures the two parts are mixed evenly and will greatly strengthen the bond.
- Always clean the area you want to glue and make sure it is dry before sanding and gluing.