A cracked solar light housing looks like a death sentence for the light. Once the plastic shell splits, water gets in, the electronics corrode, and the light dies within a season. But a crack does not have to be the end. Most solar light housings are made from thermoplastic, and thermoplastic can be repaired with the right adhesive and technique. The repair will not look factory new, but it will be structurally sound and waterproof, which is what actually matters for keeping the light running.
The key to a successful housing repair is choosing the right method for the type of crack and the type of plastic. Not all cracks are the same, and not all adhesives work on all plastics. Use the wrong adhesive and the repair fails in a month. Use the right one and the repair can outlast the rest of the light. This guide covers the three main repair methods I use, when to use each one, and how to prep the surface so the repair actually holds.
Identifying the Plastic and Assessing the Crack
Before you reach for any adhesive, you need to know what you are repairing. Solar light housings are made from several different plastics, and the repair method depends on the material.
ABS (acrylonitrile butadiene styrene). This is the most common housing material for mid range solar lights. It is rigid, slightly glossy, and usually black or dark colored. ABS is a thermoplastic, which means it can be welded with solvents. It also bonds well with epoxy. ABS is identifiable by its hard, slightly brittle feel and its tendency to crack rather than bend.
Polycarbonate. Used for clear or tinted lens covers and some high impact housings. Polycarbonate is tough and slightly flexible. It is clear or frosted. Polycarbonate does not solvent weld easily, so epoxy or specialized plastic adhesive is the way to go.
Polypropylene (PP) and polyethylene (PE). These are used for battery compartment doors and some budget housings. They are flexible, waxy feeling plastics. They are nearly impossible to glue because nothing sticks to them well. If your crack is in polypropylene, your best option is plastic welding with a heat gun, not adhesive.
ASA (acrylonitrile styrene acrylate). Found on higher end lights marketed as UV resistant. ASA looks and feels like ABS but it does not yellow in sunlight. It repairs the same way as ABS.
To identify the plastic, look for a recycling code molded into the inside of the housing. ABS is code 7 (other), polycarbonate is code 7, polypropylene is code 5, polyethylene is code 2 or 4. If there is no code, the waxy flexible test distinguishes PP and PE from the rigid plastics.
Assessing the crack. Not all cracks are worth repairing. Here is how I categorize them.
Hairline cracks (under 1mm wide) are usually cosmetic. They let a small amount of water in but the structure is intact. These can be sealed with a thin bead of silicone and do not need structural repair.
Moderate cracks (1 to 5mm wide) are structural. The housing is compromised and the crack will grow under stress. These need epoxy or plastic weld to restore strength.
Major cracks (over 5mm wide) or shattered sections with missing pieces are severe. The housing may be beyond repair. You can patch large gaps with epoxy and fiberglass mesh, but the repair will be ugly and may not hold up to wind and impact. Consider whether the light is worth the effort.
Cracks at stress points (screw bosses, mounting brackets, snap fit joints) are the hardest to repair because the repair needs to handle mechanical load. A crack at a mounting bracket that holds the light to a wall needs a strong structural repair, not just a seal.
Surface Preparation: The Step That Determines Success or Failure
I am putting this before the repair methods because it applies to all of them, and it is the step most people skip. Eighty percent of failed adhesive repairs fail because of poor surface prep, not because of bad adhesive.
Clean the area. The housing has been outside. It has dirt, pollen, sunscreen residue from your hands, and oxidation on the surface. None of these let adhesive bond. Wash the crack area thoroughly with dish soap and warm water. Scrub with a toothbrush. Rinse and dry completely.
Degrease the surface. After washing, wipe the crack area with isopropyl alcohol or acetone. This removes any remaining oils. Acetone also softens ABS and polycarbonate slightly, which improves adhesive bonding. Do not use acetone on polypropylene or polyethylene because it does nothing.
Roughen the surface. Sand both sides of the crack with 120 grit sandpaper. You want the surface to be visibly scratched, not smooth. The scratches give the adhesive mechanical grip. Sand an area about 1 centimeter wide on each side of the crack. If you are doing a structural repair, sand a wider area, 2 centimeters on each side, because you will be laying reinforcing material over it.
V groove the crack. For cracks wider than 1mm, use a small file or a Dremel tool with a cutting bit to cut a V shaped groove along the crack. The groove should be about 2mm deep and 2mm wide. This gives the adhesive a channel to fill, which makes the bond much stronger than if you just smear adhesive on the surface. The groove also exposes fresh plastic underneath the weathered surface, and fresh plastic bonds better than oxidized plastic.
Final clean. After grooving and sanding, blow out the dust and wipe with alcohol one more time. The surface should be clean, rough, and dry. Now you are ready to repair.
Epoxy Repair for Structural Cracks
Epoxy is my go to for most housing cracks because it is strong, waterproof, and bonds to almost every plastic except polypropylene and polyethylene. For those two, see the plastic welding section below.
Choosing the epoxy. Use a two part epoxy designed for plastic. The key spec is that it should be rated for plastic bonding and should be waterproof when cured. Standard hardware store epoxies (the kind in a dual syringe) work fine for most repairs. For maximum strength, use a marine grade epoxy, which is formulated to survive water and UV exposure.
Avoid five minute epoxy for structural repairs. It sets too fast to allow proper positioning and it is more brittle than slower curing epoxies. Use a 30 minute or 1 hour epoxy for structural work. The longer cure time gives a stronger, more flexible bond.
Avoid cyanoacrylate (super glue) for housing cracks. Super glue is brittle and it fails under vibration and impact. It also degrades in UV light. Save it for tiny cosmetic repairs.
Applying the epoxy. Mix equal parts of resin and hardener on a scrap of cardboard. Mix thoroughly for at least 60 seconds. Incomplete mixing is a common failure cause. The mixed epoxy should be a uniform color with no streaks.
Use a toothpick or small spatula to press epoxy into the V groove you cut. Fill the groove completely and press down so the epoxy penetrates into the crack. Overfill slightly because epoxy shrinks as it cures.
Now apply a layer of epoxy over the sanded area on each side of the crack. Lay a strip of fiberglass mesh or fine fiberglass cloth over the wet epoxy. Press it in with the spatula so it is saturated. Apply a second thin layer of epoxy over the mesh. This creates a reinforced patch, like fiberglass repair on a boat hull, and it is much stronger than epoxy alone.
For cracks at stress points, use two layers of fiberglass mesh. The extra layer adds the strength needed to handle mechanical load.
Curing. Let the epoxy cure for the full time recommended by the manufacturer, usually 24 hours. Do not handle the light during curing. The epoxy will be tack free in a few hours but it does not reach full strength for 24 hours. Curing in warm temperatures (70 to 80 degrees) gives the best bond. Cold temperatures slow curing and weaken the bond.
UV protection. Epoxy degrades in UV light. An exposed epoxy patch will turn yellow and chalky after a few months in the sun, and eventually it will crack. You must protect the repair from UV. Paint over the cured epoxy with a UV resistant paint, or coat it with a UV resistant clear coat. Any exterior spray paint works. If the housing is black, a black spray paint patch blends in reasonably well. If you want it to look cleaner, paint the entire housing so the repair is less obvious.
Plastic Welding and Silicone for Flexible Repairs
Epoxy is rigid. Sometimes you need a flexible repair, especially on plastics that flex in normal use or on plastics that epoxy will not bond to. This is where plastic welding and silicone come in.
Plastic welding with a solvent. For ABS and polycarbonate, you can weld the crack with solvent rather than adhesive. Solvent welding works by dissolving the plastic at the crack, then letting it re solidify as a single piece. The result is a bond that is nearly as strong as the original plastic.
Use ABS solvent cement (available at plumbing supply stores, it is used for ABS drain pipe) or a plastic welding solvent like methylene chloride. Apply the solvent along the crack with a small brush or syringe. The solvent wicks into the crack by capillary action and dissolves the plastic. Press the crack closed and hold it for 60 seconds. The solvent evaporates and the plastic fuses.
Solvent welding produces an invisible repair on tight cracks because you are rejoining the same plastic, not adding foreign material. It is the cleanest looking repair method. The downside is that it only works on tight cracks (under 1mm). For wider cracks, there is not enough plastic to dissolve and bridge the gap, and you need epoxy.
Solvent welding also does not work on polypropylene or polyethylene. These plastics are chemically resistant and solvents do not dissolve them.
Plastic welding with heat. For polypropylene and polyethylene, heat welding is the only option. Use a plastic welding kit with a hot air gun and plastic welding rod. The rod must be the same plastic as the housing. PP welding rod for PP housings, PE rod for PE housings.
Heat the crack area with the hot air gun until the plastic softens. Feed the welding rod into the softened area, melting it into the crack. Smooth the molten plastic with the welding tip. Let it cool.
Heat welding is not pretty. The weld bead is visible and lumpy. But it is the only way to repair PP and PE, and a properly done weld is as strong as the original material. Sand the weld smooth after cooling if you want it to look better.
If you do not have a plastic welding kit, you can improvise with a soldering iron. Heat the iron to about 500 degrees and use it to melt a piece of scrap plastic (cut from an inconspicuous area of the housing, like the inside of the battery door) into the crack. This is crude but it works for small cracks on PP and PE. The soldering iron method produces a lot of fumes, so do it outside.
Silicone sealant for waterproofing. Silicone is not a structural adhesive, but it is the best material for sealing cracks against water. Use it on hairline cracks where structural repair is not needed, or use it as a final seal over an epoxy or welded repair.
Use neutral cure silicone (not acetic cure, which corrodes electronics). Apply a thin bead along the crack, inside and outside the housing. Smooth it with a wet finger. The silicone flexes with temperature changes and stays waterproof for years.
Silicone does not bond well to PP and PE without a primer. For those plastics, use the heat weld for structure and skip the silicone, or use a silicone formulated for polyolefin plastics.
Which adhesives survive UV. This is a critical question for solar light repairs because the repair is in full sun every day.
UV resistant: Marine epoxy (with paint or clear coat over it), neutral cure silicone, solvent welded ABS, heat welded PP and PE.
Not UV resistant: Standard hardware store epoxy (yellows and chalks), super glue (degrades completely), hot melt glue (melts in heat, UV degrades it), acrylic adhesives.
The pattern is that most adhesives need a UV protective topcoat. The only repairs that survive UV without protection are the welded repairs (because the repair material is the same plastic as the housing, which was already UV stable) and silicone (which is inherently UV resistant).
A practical repair strategy for a typical cracked ABS housing: V groove the crack, solvent weld it for a clean structural bond, then apply a thin layer of UV resistant silicone over the weld as a waterproofing and UV protection layer. This gives you strength from the weld and durability from the silicone. The repair is nearly invisible and will last as long as the rest of the housing.
For a cracked polypropylene battery door: heat weld it with a soldering iron and a scrap of PP plastic. Sand smooth. No UV protection needed because the battery door is usually inside the housing.
For a cracked polycarbonate lens cover: epoxy with fiberglass mesh on the inside surface (so it is not visible from outside), then paint the inside of the repair black to block UV. The outside stays clear.
Reinforcing weak areas after repair. Once you have repaired a crack, think about why it cracked in the first place and whether the area needs reinforcement to prevent recurrence. The most common crack locations are mounting tabs, screw bosses, and snap fit joints. These are stress concentration points where the plastic is thinnest or where mechanical load is concentrated.
For a repaired mounting tab, add a small backing plate of aluminum or stiff plastic behind the repair, bonded with epoxy. The backing plate distributes the load over a larger area so the repaired plastic does not take all the stress. For a repaired screw boss, fill the screw hole with epoxy and redrill it slightly smaller so the screw fits tighter and does not wiggle. Screw wobble is what cracks screw bosses in the first place. For a repaired snap fit joint, consider replacing the snap with a small screw through the joint so the plastic clip is no longer the only thing holding the parts together.
These reinforcements add a few minutes to the repair but they dramatically reduce the chance of the crack recurring. A repaired crack without reinforcement will often crack again in the same spot within months because the underlying stress cause was never addressed. A repaired crack with reinforcement can last for years.
The housing repair that holds up best in my experience is the one that combines methods. A single adhesive rarely handles both the structural and waterproofing requirements. Weld or epoxy for strength, silicone for seal, paint or clear coat for UV. Do all three and your cracked solar light housing will outlast the electronics inside it.
One final note on when to give up. If the housing has multiple cracks, if the mounting bracket is broken off entirely, or if the housing is warped from heat exposure, the light is probably not worth repairing. A single crack is fixable. A housing that is falling apart from UV embrittlement (the plastic feels chalky and crumbles when you press it) is at end of life. No adhesive fixes UV embrittled plastic because the plastic itself has no strength left. In that case, salvage the electronics and solar panel, and buy a new light. You can sometimes transplant the good components into a new housing if you are handy, but that is a project for another day.
