Does water-based dry more slowly?
Between coats, not dramatically. Hesse SPEED-CLEAR is touch dry in around 1.5 hours at 20°C, COOL-TOP around 2 hours, the two-component PERFECT-TOP around 4 hours. All three are stackable after 16 hours.
Full hardness takes about 7 days. That is not unusual — solvent PU is the same — but it matters if you are packing and shipping on a tight turnaround, because the surface will take a mark before it has reached full properties.
The thing that genuinely slows water-based down is not the product. It is air. Water has to physically leave the film, so a still, cold, damp workshop will stretch a 2-hour recoat into something much longer. Decent, draft-free air movement does more for drying time than anything else you can change.
What temperature does my workshop need to be?
This is the real answer to most water-based failures, so it is worth being blunt. Hesse’s instruction across the whole HYDRO range is the same: do not apply or dry below 18°C, material and room temperature. The working range is 18 to 22°C. Ideal humidity is 55 to 65%.
The word that catches people out is “dry”. You can spray at four o’clock in a workshop that is 19°C, and if the heating goes off and it is 6°C by midnight, the coating has not dried. It has not just dried slowly. It has stopped.
Here is the comparison worth understanding. Solvent PU in a cold workshop will still look dry the next morning, because the solvent evaporates regardless. What it will not have done is crosslink properly, so you have a finish that feels fine and has not reached the hardness and chemical resistance you are selling. The failure is hidden, and it ships. Water-based does not let you do that. If conditions are wrong it simply will not dry, and you find out immediately.
That is a fair criticism of water-based if you want to make it one. We would say it is the more honest material. Either way, it means the workshop has to be part of the conversation, not an afterthought.
Storage matters too. The whole range needs to be kept between 10 and 30°C, so an unheated store or an overnight van in February is out of spec.
What about grain raise?
It is real, and there is no chemical way around it. Water swells the wood fibres, so the first coat stands the grain up and the surface feels rough once it dries. Anyone telling you their water-based product does not raise grain is not being straight with you.
What you can do is reduce how much it raises, then deal with what is left.
The biggest factor is drying conditions. The longer the film sits wet on the timber, the more water the fibres take up and the more they swell. Proper temperature and air movement get the water out faster, so there is less absorption time and less grain raise. That is the same workshop argument as everywhere else on this page — the two problems are not really separate.
Thinning with up to 5% Hesse HYDRO Optimizer HZ 70 works on the same principle. It speeds drying and improves pore wetting on coarse-pored timber, so the surface spends less time wet.
After that it is a sanding job. Either pre-raise the grain deliberately before you start, by damping the surface and sanding it back once dry, or let the first coat do it and denib at 280 to 320 grit. The fibres only stand up once, so subsequent coats behave normally. It is worst on open-pored oak, ash and softwoods, and barely shows on MDF or fine-pored hardwoods.
Using a filling primer rather than going straight on with a clear also helps, because it gives you a film to cut back into rather than sanding bare fibre.
Does it cost more?
Litre for litre, no. Water-based sits at broadly the same price as the equivalent PU system, so there is no material saving and no material penalty.
Where you do save is on single-component products. COOL-TOP and SPEED-CLEAR need no hardener, which is a line off the invoice. They have no pot life, so nothing goes in the bin at the end of the day because somebody mixed too much. And COOL-TOP has a 52-week shelf life against 26 for the two-component, which matters if you do not turn stock quickly.
The costs that are real are the workshop ones — heating, air movement, drying space, and the right spray equipment. Those are one-off rather than ongoing, but they are not nothing.
Is the finish as good?
Yes, and in several respects better. The coffin manufacturer we converted ended up with a better finish than the acid-catalysed system it replaced. These are not the water-based products of twenty years ago.
Are there timbers that cause problems?
A few. Oak tannins and the water-soluble extractives in ash can cause discolouration through the coating. Ash under a pastel colour needs a two-component primer underneath rather than a one-component one. Teak and other high-oil timbers can affect adhesion. None of these are dealbreakers, but they are reasons we sample first rather than converting your whole range on paper.
What else should I know?
Anything that touches the material needs to be stainless steel. Mild steel pumps, cups and lines will cause problems, so if your kit is old this is worth checking before you order product rather than after.
Interested in reviewing your finishing process?
Get in touch with the Redwood team on 02392 233310 or email [email protected] to arrange an initial conversation.