PROBLEMS with Water-Based Paint for Wood

I have a whole load of pine skirting, doorframes, window cills, pelmets, etc. to paint, and I don't much enjoy painting.

It seems that 'elf 'n' safety and environmental concerns have encouraged most manufacturers to change to water-based paints. After much deliberation, I purchased some Ronseal KnotBlock Wood Primer & Undercoat, and some Ronseal Diamond Hard Wood Paint in Pure Brilliant White Satin.

I started applying the Ronseal primer/undercoat using the recommended synthetic brush. The paint dragged and was very difficult to brush out smooth. I was painting bare pine. I asked Ronseal whether I could thin the paint for the first coat. They said I could thin the paint with up to 10% cold water (although thinning the paint isn't mentioned on the tin, or on Ronseal's website). The thinned paint was a bit easier to apply, but it was still hard work.

I encountered several problems:

  1. The paint dries quickly - much too quickly - on the brush. The drying paint causes the shorter, outer bristles of the synthetic brush to twist & curl, making the brush look like it's having a bad hair day. Washing the brush out in water every 15-30 minutes seems to be the only way of resolving this.

  1. The drying paint quickly causes the brush bristles to clump together. This makes it very difficult to paint curves or mouldings because instead of the bristles fanning out evenly over the contour, the brush simply splits into two or three clumps, thereby missing much of the surface. Again, washing the brush out in water every 15-20 minutes seems to be the only way of resolving this.

  2. I keep getting tiny lumps in the paint. At first I thought these lumps were actually in the paint. Now I think they are small pieces of partially-dried/hardened paint dropping off the brush bristles, even though I wash the brush clean every 15-20 minutes. I have resorted to lightly rubbing down the paint between coats to remove these lumps.

The cause of these problems appears to be that the paint starts to harden within the brush bristles very quickly and the process of adding more paint to the brush as the painting proceeds does not stop this hardening process. I never experienced any of these problems with spirit-based paints.

Maybe I need to change my technique, or maybe this is as good as it gets with modern, environmentally-friendly, water-based paints - I don't know.

I would welcome any advice or comments before I become totally pi$$ed off and abandon the project.

Maybe someone could recommend a better make/type of paint for wood that does go on smoothly and doesn't require the brush to be washed out every few minutes (a friend has suggested Dulux Trade paints)?

Thanks

Reply to
Interloper
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I rather like Wilkinson's water-based silk paint. Used with a small short-pile roller it made a smashing job of radiators and panelled doors.

Reply to
Skipweasel

It sounds to me that the wood is a bit too porous and is absorbing all the water solvent, perhaps an even thinner application would suffice and apply more that one coat, the first coat applied very thin just to seal the wood, then try the second coat when the first is thoroughly dry. This particular water based wood primer is supposed to dry in about six hours, not six minutes.

Stephen.

Reply to
stephen.hull

I always use International brand primer/undercoat - applied with a 'proper' brush - and don't have the problems described above. Water based gloss is also fine for doors and skirting boards. Don't use it on internal window sills on which plant pots etc. will be stood - the paint discolours under the pots. It's also no use on MDF surfaces which may get wet - kitchen window sills, etc. - water causes little pimples to appear on the surface. You can still get oil-based external grade gloss if you shop around.

Reply to
Roger Mills

The problem I found with water based primer was that it raised the grain, so that the surface the joiner had just spent time sanding was now a series of ridges and furrows. Fine if you want that, but it wasn't the effect I'd hoped for. It wasn't really unexpected - that was why I'd told the painter to use an oil based primer - but of course the chap doing the job thought he knew better...

Reply to
docholliday

I wonder what they use as a thickener/medium in these water based paints other than the pigmment? Usually with an oil base the oil itself is generally thick enough to create the coverage without being absorbed too much.

Stephen.

Reply to
stephen.hull

Primer is very much something that fills the grain, and keys to the wood below, and also provides a good base for the pigmented undercoat that goes above.Water based primers are thick and fast drying and that's fine, you simply need to sand the thing smooth before the undercoat goes on, using (probably wet) and dry paper, wet.

Reply to
The Natural Philosopher

If water based primers are thick and fast drying what do they use as a thickener? In my experience the water based primers I've used have always been quite thin, again as opposed to an oil.

I know primers and undercoats contain more solids and less solvent/oil to provide the coverage, whereas the water based types appear to lack even more in pigment.

Flatting down between coats is normal practice anyway whether its done wet-or-dry but more heavier flatting will be necessary if the grain has been raised too much especially if you want to achieve a finer finish.

Obviously the more solvent it contains the more it will soak in but there has to be a compromise on how much will soak in and how fast it dries.

This Ronseal primer mentioned appears to be drying too fast which would normally give less time for the solvent to absorb into the wood, but if the wood is particularly porous then it will soak up solvents like a sponge which is what I'm guessing is happening to the OP.

Stephen.

Reply to
stephen.hull

Thanks for all the comments and advice.

I spoke to Ronseal Technical today and they are replacing the paint so I can try a different (fresh) batch to see if the problems persist. They are also taking my old paint back to see if there is anything wrong with it.

Personally I think the problem is that the water-based paint rises up inside the brush bristles by capillary action and immediately starts to harden. This quickly causes the brush to stiffen and the bristles to clump together, rendering the brush inflexible and ineffective. Regularly and frequently washing the brush out seems to be the only viable workaround. Maybe employing two synthetic brushes, one in use, the other soaking in water, and swapping them every 15 minutes or so is the answer. It's a lot of faffing around!

Water-based paints seem much more difficult to apply and brush out smoothly than traditional spirit-based paints. Another 'wart on the arse of progress', as my work colleague is often heard to say.

I'll report back after I have tried the replacement paint.

Reply to
Interloper

This is the problem with all surface coatings, solvent or water based. In an ideal world none of the solvent gets absorbed into the substrate and the film forms in ideal conditions (glass is often used to test paint films).

Acrylic resins require a minimum film forming temperature (MFFT), below which they just craze into a white powder. At one end of the scale you have a resin that will cure at anything above freezing but has the properties of cling film. Those that are as hard as perspex require upwards of 20 degC, so can only be applied in a controlled environment. Coalescing solvents can lower the MFFT but only at the expense of drying time, so it's easy to see why most water based systems for domestic use are something of a dog's dinner.

Reply to
stuart noble

It would be better to seal the bare wood with shellac first to stop the absorption rate, then apply primer etc.

I want to paint my internal doors and woodwork with a more none yellowing paint than a synthetic gloss, even the expensive white gloss paints still go yellow after a couple of years. The only way I can see of achieving this is by using a water based type of acrylic or even a vinyl silk emulsion but none of these types of paint can live up to the application of an oil.

Stephen.

Reply to
stephen.hull

A pva seal would be as effective as shellac though not as hard/brittle. IME the white acrylic primers work pretty well on most surfaces, it's the satin/gloss topcoats that are crappy (although they are 100% non-yellowing). To get the twin properties of hard wearing and non-yellowing you need specialist solvent based polyurethanes, which are mighty expensive and not easy to find. My compromise would be 2-3 coats of primer/undercoat sanded smooth followed by the thinnest possible coat of gloss

Reply to
stuart noble

My experience has been that by the time you have the surface smoothed again all the parts which were raised by the water based primer are now completely bare again, so needing another coat of primer...

Reply to
docholliday

PVA would work but it may raise the grain more as its water based and will take longer to dry than shellac which is almost instant drying which is why it was used on bare wood for coach work.

My internal doors (which are new) I have already painted in white emulsion the architraves and skirting are still in gloss, I intend to repaint over the gloss with an emulsion type finish to avoid the yellowing you get with an oil.

Unfortunately a thin coat of gloss will still yellow.

Stephen.

Reply to
stephen.hull

Using a water base primer sort of defeats the object, at least with a good coat of oil primer you can flat without worrying too much about rub-through, although its the undercoat which is supposed to be wet flatted after you have built it up, but we can't seem to find a suitable water based primer that has the same body as an oil to build up with.

Stephen.

Reply to
stephen.hull

I have used up to 15 coats of primer rubbed back to the wood to get perfect 'plastic' finishes on wood..frankly if all you want is a covering coat that lets the grain show through, why not let the brush strokes show through?

Water based primer actually worked pretty well for me. The under and top coats were oil, tho :-)

Reply to
The Natural Philosopher

Indeed - after I'd smoothed the surface I then primed it with the oil based primer I'd specified, which allowed me to put on the rest of the coats with just flatting the undercoat. That's why I was annoyed that the person supplying the door for me to fit had used the water based primer instead of oil based - if I'd known he only had water based primer available I'd have told him to supply it unprimed.

Mike

Reply to
docholliday

15 layers seem pretty excessive though just to build up with, you could half that with oil primer, but of course you have to wait longer for it to dry, I can't see carriage or coach builders using water based crap.

I have/want absolutely no brush-marks showing on any of my paintwork, (well I would wouldn't I). The finish I have at present on the new doors is ideal because it has the grain effect look as a finish, I just want them all to remain white when I paint them, however the other gloss paintwork is like glass but that is all done in oil paint, water base is horrible.

You can get a good finish with vinyl silk emulsion which is a compromise between staying white and being easy to wipe clean, but you have to work much faster an use the right brush, but for application and ease of use you can't beat an oil base.

Stephen.

Reply to
stephen.hull

You can build up fantastic layer/s in oil, I've yet to be impressed with any water base primer.

Stephen.

Reply to
stephen.hull

A thin coat of acrylic gloss won't though

Reply to
stuart noble

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