Amazing adhesives

Sunset, Nov, 1988

Are you searching for that one allpurpose, fix-anything glue? Forget it; the range of jobs calling for a dab of sticky stuff is so vast that no single glue could possibly do it all.

And even if there were such a glue, you'd be lucky to find it. Go to a hardware store or home improvement center: you'll find dozens of formulas, an inordinate number of which claim they can bond anything to anything.

So how do you know which glue to use? To help, we describe 10 glue types and their uses in our listings here and on pages 110 and 112. In addition, we touch on specialty adhesives and tell you the closest thing out there to an all-purpose glue.

Specialty glues: sometimes they're the perfect choice

There might not be a perfect glue for all jobs, but sometimes there's the right glue for a specific job.

For example, plastic adhesives bond specific types of plastic, using a solvent to melt and fuse the pieces together. Get the formula labeled for each specific plastic, such as PVC cement for PVC pipe.

Vinyl resins bridge slits and tears in vinyl and fabric upholstery, rainwear, luggage, and pool toys. Water-base versions work on fabrics, so long as joints aren't seriously stressed. Glues flex when dry, and stand up to washing and drying.

Specialty epoxies and cements include epoxy steel and bars and plastic metal. They adhere to the aluminum, steel, or other material to which they are applied, filling gaps and drying to the same rockhard consistency. Once dry, they can be filed sanded painted drilled or tapped Glues for repairing glass and china

bond clear, bridging gaps and filling chips, even on windshields. Sunlight cures some of these adhesives, so what you're repairing must be transparent, For other types, follow the guidelines for household cement (see listing below). Before applying, check heat and water ratings (they should be on the label). It's no fun when a repaired plate, after a few trips through the dishwasher, goes to pieces again.

Silicone: a possible all-purpose?

The silicone glues we use today often function like sticky caulk, filling gaps and drying to a rubbery, flexible bead. Silicone formulas are some of the few adhesives you can apply at low temperatures (even below freezing); they stay strong and flexible at temperature extremes.

Silicone joints flex when dry, which may be-or may not be what you need. They weather well, don't shrink, and resist water, oils, oxidation, and damage ftom ultraviolet rays. Silicones stand up to vibrations and are also flame retardant (many other glues are highly flammable). Most will work on kitchen repairs; make sure you choose one that's safe to use around food. Some contain fungicides to prevent mold when used on surfaces that tend to get wet, such as bathroom tile.

The more chemists work with this already useful glue, the more they realize its potential as an all-purpose adhesive. Still in its "Model T phase," as one chemist told us, this glue may some day become the dominant glue type on the market.

A little basic terminology

Here's a quick glossary of terms you'll find either in our listings or on adhesivecontainer labels.

We all say that glue dries, but the correct word is to cure. Each glue does this in one of three ways: by evaporation, as with solvent- or water-base glues; by cooling, as with thermoplastic glues; or by polymerization-chemically changing from liquid to solid-as with epoxies and some of the other specialty glues.

Green strength is a glue's ability to grab while wet. Green time means the time between application and solidification, when you can still reposition pieces.

Some glues add tackifiers to make them sticky when wet. However, don't be overreliant on these ingredients; a glue's initial holding power doesn't guarantee a lasting bond. Use a clamp (see information in box at right).

Fixturing time is how long you have to wait before handling pieces.

Pot life is the amount of time a two-part adhesive, such as epoxy or resorcinol, remains usable after mixing.

Some application tips

Clean all surfaces before you start. If you don't, the glue will fasten to dirt, grease, or dust more than to the surface you're trying to glue; joints may fail.

Follow the safety recommendations on labels, especially for solvent-base glues; proper ventilation will save you, at the very least, a nasty headache.

Mix two-part adhesives carefully and thoroughly. With all adhesives, use the amount specified; too little or too much may ruin the bond.

Almost all glues do better when applied at room temperature; most don't do well in the cold. As one epoxy label states, "Like peanut butter, this glue mixes and spreads easier at 80 [degrees] than at 40 [degrees]. You can speed most cures with heat, usually with either sunlight or a heat lamp, but don't overdo it; some solvent and polymer adhesives can actually burst into flame if overheated.

Above all, be patient; let glues cure completely. If possible, clamp the joint tightly throughout the drying process (again, see box at right)..