Can I use Milton Fluid to clean my roof?
Quick answer: We'd say no. Milton Fluid is a sodium hypochlorite steriliser -- diluted bleach -- and while it will kill the green growth on a soft-top, it isn't selective: it attacks the dye, the stitching thread and the waterproofing at the same time. It can leave you with a faded, patchy hood and a roof that no longer keeps water out. Use a dedicated fabric hood shampoo instead.
Milton Fluid is a UK household sterilising product, best known for baby bottles and weaning equipment. Its active ingredient is sodium hypochlorite -- the same chemistry as kitchen bleach, just at a gentler concentration. That gentleness is exactly why it gets recommended on owners' forums for shifting algae, moss and light lichen off a fabric roof. The trouble is that "gentle bleach" is still bleach, and a convertible hood is one of the worst surfaces to test that theory on.
The chemistry, and why it matters here
Sodium hypochlorite cleans by oxidation: it breaks chemical bonds in whatever organic matter it lands on. A green roof is just a colony of living organisms, so the bleach kills it efficiently. The problem is that oxidation makes no distinction between the algae you want gone and the things you want to keep. Your hood's dye is an organic pigment. The stitching is cotton or polyester thread. The factory waterproofing is an organic coating bonded to the weave. All three are fair game for the same reaction that lifts the green.
This is the part the forum threads tend to skip. People report success because, on the day, the green disappears and the roof looks clean. The damage shows up later: a faded stripe where the solution ran, a seam that starts wicking water after the next downpour, a patch of canvas that drinks rain rather than beading it. By then nobody connects the cause to the Milton.
What actually fails first
Three things take the hit before the main canvas does, and they fail in a predictable order.
- Waterproofing. The factory proofer is the thinnest, most exposed layer, so it strips first. A roof that beaded water beforehand will start to wet out and look dark when it rains.
- Stitching. Seam thread has far less material than the panels around it, so the same dose of bleach weakens it disproportionately. Seams are also where leaks begin.
- Colour. A dyed hood loses tone unevenly, leaving lighter patches that only a roof dye can put right -- and dyeing a whole roof to fix one bleach mark is a job out of all proportion to the original green stain.
One we saw on the bench
Tom, our operations manager, took in a black German cabriolet a couple of summers back where the owner had cleaned the green off the rear quarters of the hood with a diluted steriliser. The roof looked clean enough at a glance. But hold a hose on it and you could see two pale vertical streaks where the solution had run down toward the deck, and along the lower seam the thread had gone chalky and brittle. The green was gone; so was the colour match and a good stretch of the proofing. Re-dyeing and re-proofing that roof cost a multiple of what a bottle of hood shampoo and an afternoon would have. The owner had done nothing reckless -- they'd diluted it, they'd rinsed -- but the chemistry doesn't care how careful you are.
How to spot bleach damage before it spreads
If a steriliser or bleach has already been used on a hood, the signs are readable once you know what to look for, and catching them early decides whether you're looking at a touch-up or a full re-dye. Start with the roof dry and in good light, then wet it and watch how it behaves; the two states tell you different things.
- Faded stripes or run-marks. Bleach concentrates wherever the solution pooled or ran, so the classic tell is a pale vertical streak running down from where it was applied toward the lower deck or the rear screen surround. The fade is sharp-edged rather than gradual, because it follows the run line.
- Whitened or chalky stitching. Run a fingernail gently along a lower seam. Healthy thread is supple and colour-matched; bleached thread goes pale, stiff and dusty, and can shed fibres. This is the early-warning sign for a leak that hasn't started yet.
- Wet-through patches in rain. Hose the roof or wait for a downpour and look for areas that turn dark and stay dark instead of beading. That darkening is water soaking into the weave rather than sitting on top: the proofing has gone there.
- A musty or damp smell inside. A roof that no longer sheds water lets moisture into the headlining and the cabin, and the first thing many owners notice is the smell, not the stain.
The cruel part is the sequence: the cosmetic fade shows up within days, but the waterproofing loss and the seam weakening often don't announce themselves until the next sustained wet spell, by which point the cause is weeks in the past.
What recovery actually involves
Once bleach has done its work, you're no longer cleaning a roof, you're restoring one, and that's a different order of job. There are broadly two routes, depending on how far it has gone.
If the damage is limited to lost waterproofing and the colour still reads even, recovery can be as simple as a thorough clean, a full dry, and a fresh coat of proofer applied on a warm, dry day so it cures into the weave. That's the lucky outcome, and it's the one you get when someone catches the wet-through early and hasn't scrubbed the dye off as well.
If the colour has gone patchy, you're into re-dyeing. A spot repair almost never works on a fabric hood, because a fresh dye patch sits brighter than the weathered fabric around it and the join shows; the honest fix is to clean, prep and re-dye the whole panel or the whole roof to a single even tone, then re-proof over the top once it has dried. That is hours of careful work with a roof dye that has to be brushed or sprayed into the weave evenly, and it's why the bench example earlier cost a multiple of the original shampoo-and-afternoon job. Where the stitching has gone brittle, re-dye and re-proof won't rescue thread that's already failing; a weak seam eventually needs re-stitching, which is a trim job rather than a detailing one. The whole point of avoiding the bleach in the first place is to stay out of this paragraph entirely.
Why a hood shampoo wins
A specialist fabric hood shampoo is built around the opposite priority. It lifts grime and growth at a pH the fabric, dye and stitching can tolerate, and it leaves the waterproofing in place rather than stripping it. It won't out-muscle bleach on a thick, established green mat in a single pass; you might need two goes and a soft brush. But it carries none of the bleaching or thread-rot risk, and you don't have to mask anything off before you start. On a surface as expensive and as hard to repair as a convertible hood, the slower, safer route is the cheaper one.
The other thing a dedicated system gives you is a matched proofer. The better fabric-care ranges sell a cleaner and a waterproofer designed to work together: the cleaner doesn't strip the proofer, and the proofer bonds to fabric the cleaner has prepared. Names the trade reaches for include Renovo, whose fabric hood cleaner and proofer set is the long-standing default; Autoglym's convertible products, which are easy to find on the high street; and 303, whose fabric guard is well regarded for re-proofing. We don't push a single brand as the only answer; what matters is that the product is sold specifically for fabric convertible roofs and pairs a cleaner with a proofer, rather than a general-purpose cleaner pressed into a job it wasn't designed for.
The other household remedies, briefly
Milton isn't the only thing people reach for, and the alternatives are not obviously better. Each one fails the fabric in its own way.
White vinegar (acetic acid) is mild enough to shift light lichen and is sometimes suggested as the "natural" option, but it won't sterilise the weave, so the growth returns within weeks; used strong or left to dry in, the acid can also dull the dye and leave the fabric feeling stiff. Washing-up liquid is too weak to touch established green and, worse, leaves a surfactant residue that holds onto dirt and can interfere with any proofer you later try to apply, so the roof gets grubby faster afterwards. Patio, decking and fence cleaners are the worst of the lot: they often carry stronger biocides than Milton, are designed to bite into stone and timber, and are explicitly not formulated for textiles, so they strip dye and proofing with no margin at all. Pressure washers belong in the same warning, by the way: even with a gentle cleaner, the jet drives water through the weave, frays the stitching and lifts the proofing, undoing the very thing you're trying to protect.
If you genuinely insist on a household product, Milton is among the more measured picks -- but "least bad of the DIY options" is still a long way short of "right for the job", and none of these saves you money once you price in a re-dye.
If you ignore all of the above
We'd rather you didn't, but if you're set on trying it, the harm-reduction version looks like this. Dilute to the label's sterilising ratio, never stronger. Test on a hidden corner and wait for it to dry before judging the result. Mask off every seam, the rubber seals and any painted trim. Apply with a soft brush in shade, keep the fabric wet so the solution can't concentrate as it dries, and rinse with clean water at least twice. Then let it dry fully and re-proof on a warm, dry day, because you will have stripped whatever waterproofing was left. Keep it well away from mohair roofs, freshly proofed hoods and any fabric that already shows wear or faded dye.
After any clean, re-proof
Whatever lifts the growth leaves the fabric exposed, and spores can re-establish within weeks on a roof that isn't protected. Once the hood is dry, check for any lifted colour that needs a touch-up, then apply a proofer on a warm, dry day so it cures properly. Between cleans, keep the car out of automated car washes -- the detergents and brush pressure they use are no friend to a fabric hood, and they will work proofing loose faster than weather alone.