There are many types of plastics and as many varieties of glue; choosing the wrong combination creates a bad job, a weak fastening and, in rare cases, the object that should be repaired is damaged even more. Read the article to learn how to choose the right adhesive for your project and then follow the instructions to make sure you create a permanent bond. If you need to join plastic tubes together, you can go directly to the dedicated section, where you will find specific instructions for choosing the glue and the procedures to follow.
Steps
Part 1 of 3: Choose the Glue
Step 1. Look for the recycling symbol
Different types of plastics need different adhesives. The easiest way to identify the material is to look for the recycling symbol printed on the plastic itself, on the label or on the packaging. This symbol is a triangle formed by three arrows and contains a number, a letter or both inside it. Alternatively, the alphanumeric code can be found immediately under the triangle.
Step 2. Learn how to glue the plastics identified with the number 6
When the recycling triangle contains the number
Step 6. or letters PS it means that it is "polystyrene". This material is best bonded with a polymer adhesive or a specific glue such as Loctite epoxy. The other glues that work are cyanoacrylate (also called "instant glue" or "cyano") and epoxy ones.
Step 3. Choose a special glue for plastics marked with the number 2, 4, or 5
If the material you need to glue is labeled with codes
Step 2
Step 4
Step 5., HDPE, LDPE, PP or UMHW you are dealing with "polyethylene" or "polypropylene". These are very difficult plastics to glue and you need to get special stickers that also have the name of these materials on the label.
Step 4. Plastics with the symbol 7 or 9
Materials that fall into the mixed category with the number
Step 7. And ABS identified with the number
Step 9. are plastic resins, sometimes you can find other letters that better specify their nature. You should use epoxy glue or cyanoacrylate.
Step 5. Try to identify the type of plastic differently
If there is no recycling symbol, you must try to understand the material you need to glue before choosing the glue. Here are some useful guidelines:
- Lego bricks are made of a material called "ABS" and are glued with epoxy adhesive. An ABS glue is also fine but could alter the surface of the object.
- Fake glass, cheap games, CD cases and other similar items, often made of clear plastic, are made of "polystyrene" and can be glued with different types of adhesive. If you want to get the best results, use a polymer cementite or a specific glue for plastic materials.
- If you have to glue thick and hard plastics such as those of bottles, buckets, packing crates or food containers, then it is better to choose an adhesive that has the words "for polyethylene" and "for polypropylene" on the label. It is impossible to bond these plastics with most normal adhesives. Do not assume that a glue that says "for plastic" is effective in this case, unless it also specifies "polyethylene" or "polypropylene".
Step 6. Do more research online if you need to bond plastic to another type of material
If you want to glue plastic to wood, metal, glass or even a plastic of a different nature, then you need to engage in some further analysis. If you can't find a solution online or by asking a DIY expert, go to the paint shop and check all the stickers on it to find out which one you can use. The label on the glue package should tell you which materials it works with.
- You can find many sites online that provide you with all the information you need. Do not forget also the official web pages of the glue manufacturers, you will surely find the solution that is right for you.
- If in doubt, try the adhesive on a scrap piece that is the same material or on a hidden corner of the object you want to glue.
Part 2 of 3: Gluing the Plastic
Step 1. Remove any grease from the plastic
Wash the piece with soap, a specific detergent or soak it in isopropyl alcohol. Dry it thoroughly.
Then avoid touching the plastic with your bare hands to minimize sebum residues
Step 2. Sand the surface to be bonded
Use 120-200 grit sandpaper to create a rough surface that allows for glue to bond. You can also use steel wool or emery wool, but remember to scrub only for a short time.
Step 3. If necessary, mix the two glue components together
Two-component "epoxy" adhesives are sold as two ingredients that must be mixed together to become active. Read the instructions on the package because each type of glue requires certain proportions between the two ingredients. Some can be used even after several hours of mixing, while others must be applied within a few minutes.
Read the 'Choosing the Glue' section to find out which type of adhesive is best to use. If you are not applying two-component glue, you can skip this step
Step 4. Apply glue to both surfaces
Use a small brush for this and be sure to apply a thin layer of glue where the two surfaces will come into contact. If the objects are small, such as a broken plastic model, you can use the tip of a needle to spread the glue.
If you are using a solvent-based adhesive (not polymer or plastic cementite), you must first secure the two objects with clamps and then use a bottle with applicator to spread a thin line of adhesive along the edges. At this point the solvent-based adhesive will run between the two surfaces. If you need to join plastic pipes, read the section 'Gluing a Plastic Pipe'
Step 5. Press the two objects together
This allows you to remove air bubbles; However, try not to push so hard that the adhesive runs out. If this happens, wipe off the excess glue with a cloth unless you are using acrylic cementite which must be allowed to evaporate.
Step 6. Keep the two objects firmly in place
Use a vise, rubber bands, or tape to keep them from moving. Read the specific instructions of the glue you are using to know the laying times. Depending on the brand of adhesive, times can vary from a few minutes to 24 hours.
Many adhesives continue to react and develop a stronger bond for days or even weeks after application. Avoid applying pressure or heating glued objects in the first 24 hours after application, even if you feel the grip is firm
Part 3 of 3: Glue a Plastic Tube
Step 1. Find out what tube it is
There are three types of plastic tubes and each reacts to only one type of glue. The easiest way to identify them is to read the universal recycling symbol, a triangle formed by three arrows with a number or letters written inside. Read the 'Choosing the Glue' section for more information on this.
-
PVC pipes are the most used in residential construction, although they should not be used for high temperature and electrical systems. They are usually white or gray if they are used in industrial plants. The recycle symbol is
Step 6. or PVC.
- CPVC pipes are PVC pipes treated to withstand high temperatures. They have the same recycling symbol as the PVC ones (6 or PVC) but are brown or cream in color.
-
ABS is an older, more flexible material used in plastic pipes. It is usually black in color and should not be used to carry drinking water. In some regions, it is even forbidden for any plant. Its recycling symbol is
Step 9., ABS
Step 7..
- PEX pipes are the newest and are available in many colors. They are not recyclable nor can they be glued. Mechanical joints are used to be joined together.
Step 2. Choose the glue
The material that joins the plastic pipes is called solvent-based cementite. Find the specific one based on the tube material you need to machine.
- Solvent-based adhesives for ABS only join this type of pipes together just like adhesives for PVC and CPVC.
- To fix ABS and PVC pipes you need to use a transition solvent adhesive. It is green in color and easy to identify.
- If you can't find a specific product, use a universal solvent adhesive for all combinations of PVC, CPVC and ABS. You should always rule out that it is PEX because this material does not respond to glue.
- Read the label on the glue to make sure it also works for the diameter of the tubes you need to glue.
- To fix a plastic pipe to a metal one, you need to get a specific adhesive for this kind of combination or rely on a mechanical joint. Contact a plumber or ask the hardware store clerk for advice.
Step 3. Follow all safety procedures regarding ventilation
Primers and solvent-based adhesives release dangerous vapors. Work in a room with excellent air circulation (large, open windows and doors) or use a respirator mask that blocks organic vapors.
Step 4. If the pipe has been sawn, smooth it out
Roll a sheet of 80-grit sandpaper inside the tube and sand both the inside and the outside, where you will need to glue. You need to remove any rough edges left by the saw that may over time capture debris and cause obstructions.
- Flatten the sandpaper over the tube to make it adhere well over the entire surface before you start scrubbing.
- If you don't have sandpaper, use a file or remove the most noticeable imperfections of the cut with a small knife.
Step 5. Line up the pipes properly if you need to connect them with a curved fitting
Once you have applied the glue you will not have much time to fix the pipes; then combine them dry in advance. Line them up as you need to and use a marker to draw reference lines.
Step 6. Apply the primer
Among the three plastic materials that are used for pipes, only PVC must be treated with the primer; for the CPVC it is not essential, but the result will be better. Apply a PVC or CPVC primer as directed on the product packaging. You will need to lay it out inside the female segment and outside the male segment. Wait for it to dry for 10 seconds before continuing.
Step 7. Work quickly and methodically when applying the solvent adhesive
Wear gloves, use a brush or cotton swab, and spread an even layer of adhesive on the outside of the male tube and inside the female tube. Put only a thin layer, if you exaggerate the adhesive residues are dispersed in the tube and over time can cause fillings.
Step 8. Immediately insert the tubes into each other but with a quarter turn off the desired location
Rotate the tubes a quarter of a turn to bring them to the alignment you decided earlier. If you didn't make any reference marks on the tubes, just rotate them for a quarter of a turn. Hold them in place for about 15 seconds to give the adhesive time to set.
Step 9. Correct any errors by cutting the pipe and creating a new connection
When the solvent-based adhesive dries, the plastic tends to crumple a little; if your tube turns out to be too short, glue another segment. If it is too long, remove a segment that includes the glued area and reattach the tubes with more adhesive.
Advice
- A silicone putty is useless on plastic, unless it is a purely aesthetic item, because it is not a structurally robust solution.
- If you drip acrylic concrete onto a surface you don't want to glue, don't clean it. Just let it evaporate.
