What is butyl tape, how do you use it, and what does it not stick to? The types, where it goes on a metal roof, butyl vs silicone, flashing tape, wet surfaces, shelf life, removing old butyl, and what the tape will and will not do
Butyl tape is a strip of synthetic rubber sealant (polyisobutylene) that never fully cures: it stays tacky and pliable for years, seals by being compressed between two surfaces, and comes either bare (a gray or black rope or strip on release paper, for seams and lap joints on metal roofs, RVs and windows) or backed with foil, fleece or a film so it can be exposed to weather as a flashing tape. It sticks to clean, dry metal, glass, masonry, wood, most plastics and cured roofing; it does not stick to wet, dusty, oily or frosted surfaces, to silicone, to soft PVC, or to anything below about 40°F without priming. Its limits are the flip side of its strengths: it stays soft, so it creeps under load, it is not a structural adhesive, and bare butyl must be covered.
C&R Butyl Magic BT2-WHITE Butyl Tape, 2 in, Foil Backed, WhiteThe product data lists Butyl Magic BT4 as a 4 in self-adhesive foil-backed sealing tape in a 50 ft rollWhat makes butyl different from every other tape. Ordinary tapes carry a thin layer of pressure-sensitive adhesive on a backing and hold by that film alone. Butyl tape is almost all sealant: a thick (30 to 60 mil and more) layer of rubber that flows into the texture of the surface under pressure and keeps flowing, slowly, for the life of the joint. That is why a butyl lap seal on a metal roof is still sealing twenty years later and why the same tape squeezes out of a joint that is over-compressed. Everything people ask — its disadvantages, the types, how to apply it, what it will not stick to, whether something is better, whether flashing tape keeps water out, wet surfaces, shelf life, removal — follows from that one property, and the cards below take them in order.
Butyl and flashing tape, question by question
Widths, backings and roll lengths are from the Butyl Magic product data; application limits are the ones printed on the rolls.
Butyl tape in plain words
- Butyl is a rubber sealant that never cures; it seals by being pressed into the joint and staying soft.
- Bare butyl goes under panels and fixtures and must be covered; foil-backed butyl is weatherable and goes over seams and repairs.
- It sticks to clean, dry metal, glass, wood and cured roofing; it does not stick to wet, dusty, oily, frosted or silicone-touched surfaces, or soft PVC.
- Apply above about 40°F, peel as you go, overlap 2 inches shingle-fashion and roll the whole length hard with a seam roller.
- Not for wet surfaces; use a wet-surface roof cement in an emergency and come back dry.
- It creeps, it is not structural, it cannot be painted unless fleece-backed, and it is messy in heat.
- Silicone for glass, polyurethane for paintable structural joints, butyl for laps and re-sealable seams.
- Shelf life about two years cool and dry; in service under cover, decades.
Questions people ask
What are the disadvantages of butyl tape?
It never hardens, so it creeps under load and squeezes out of over-tight joints; it is not structural; bare butyl needs cover from UV; it will not take paint unless fleece-backed; and it is messy in heat and stiff in cold.
What are the different types of butyl tape?
Bare rope or strip for compression seals; foil-backed for exposed repairs; thick 60 mil foil for rough surfaces; fleece-backed for coating over; copper butyl for copper and lead; and window flashing tape with a film face.
How do I use butyl tape?
Clean and dry the surface, work above about 40°F, peel the paper as you unroll, overlap 2 inches shingle-fashion and roll the full length with firm pressure.
What does butyl tape not stick to?
Wet, frosted, dusty, oily or chalky surfaces, silicone, soft PVC, polyethylene and Teflon, and cold surfaces until warmed.
What is better than butyl tape?
Nothing for lap seals under metal panels. Silicone is better on glass, polyurethane for paintable structural joints; each is a different tool.
What can I use instead of flashing tape?
Metal flashing bedded in butyl or sealant, liquid-applied flashing, or a strip of membrane set in adhesive; all more work than tape.
Where can you get butyl tape?
Roofing and metal-building supply houses, and from us by the roll in widths from 2 to 39 inches; the band on this page has the current prices.
Does flashing tape keep water out?
Yes, when lapped so water runs over the laps and rolled into clean, dry substrate; it fails at reverse laps and on wet surfaces.
What does butyl tape do?
Seals joints that move: metal roof laps, fixtures, window fins, gutter seams and roof repairs, by staying soft and pressed into the joint.
How permanent is butyl tape?
Under cover, decades; exposed bare butyl degrades in UV in a few years, which foil backing prevents.
How to remove old butyl tape?
Lift an edge with a plastic scraper, warm with a heat gun on low, pull slowly and clean the residue with mineral spirits or a citrus cleaner.
Can butyl tape be applied to a wet surface?
No; it will lie there but will not bond. Use a wet-surface roof cement for the emergency and return when dry.
Is butyl better than silicone?
For laps, re-sealable seams and anything that will be coated, yes; for glass and metal-to-metal joints that stay bare, silicone.
Does butyl tape ever harden?
No; it skins slightly on an exposed face and stays pliable underneath for its service life.
What is the shelf life of butyl tape?
Typically about two years from manufacture stored cool and dry.
How to use butyl tape for metal roofing?
Rope in the side and end laps and at closures under the panels; foil-backed tape rolled hard over fastener rows, seams and holes on an existing roof, at least 2 inches of bond each side.
Related guides
Roof cement, sealant and primerASTM D4586 and D41, and removing tarSeam rollers and single-ply toolsTPO, PVC and EPDMCaulking gunsThrust ratio, dripless, sausage and pneumatic gunsRivet guns and pop rivetsSizes, materials and setting a rivetRoof anchors by roof typeWood, standing seam, corrugated, tile and membraneThe ratings, test results and standards shown here are the manufacturers' published values, reproduced as published. Nothing on this page is a recommendation by Bayshore Safety that any product is suitable for a particular task, hazard or workplace. Selecting safety products and protective equipment is the responsibility of the end user and the employer, based on their own hazard assessment and the regulations that apply to their work. Confirm every value on the manufacturer's own documentation before use.