Professional finish on bare timber using water-based paint only
Update from April 2011 Discussions about painting bare timber using water-based paint only, still usually conclude with – you can’t beat oil for a basecoat. True – usually. Usually, for a good finish in water based paints ie acrylics, you need a sound oil-based surface to paint over. So if you are redecorating over previous oil paint, there is no reason why an all-acrylic system won’t work well, whereas from new, if you want a good base on new timber for topcoats of acrylic eggshell or gloss, there isn’t much out there to compete with 2 coats of oil based Coverstain primer or Tikkurila Otex. On new timber, filling is always a requirement.
But what do you do if you need a 5 star finish on new or scaggy previously painted woodwork, and you can’t use any oil paint whatsoever?
Recent clients didn’t want the odours, or the pollution from off-gassing oil paint, but they still wanted a very classy traditional brush finish! Tricky. Just using 4 conventional coats of water based paints and conventional fillers, it’s probably not viable, and you would need to “have a word to manage expectations” but with a bit of effort, that is what they got.
Rather than go round and round in circles looking for the ultimate (but still sub standard) acrylic primer undercoat and eggshell, I have been going back to basics. Look at a good finish from the other end. The prep. It is all in the filling!
The way I think is: if the surface is rock solid and well filled and prepared, the choice of top coat becomes less of an issue ie with a good base, all your topcoats have to do, is lay on evenly. They don’t have to try (and fail) filling any surface imperfections. If you think about MDF, which tends to start “perfect”, with a good basecoat, most acrylic eggshell topcoats will look pretty solid.
So how do you get a really solid base for acrylic eggshell on dinged up or new woodwork? And quickly? The answer lies in the right choice of fillers.
Artists need to make their canvasses smooth before painting, and the surface has to be flexible enough to cope with the canvas moving in different temperatures etc. They use liquid Acrylic gesso, (as opposed to olde worlde gesso made from rabbit glue size.)
For mouldings on tops of skirtings and architraves, I highly recommend adding a couple of coats of acrylic gesso to the filling process for a high class finish.
1 – Prime bare/previouly painted timber first with Classidur Universal Primer, or Mythic Universal Primer, or a water-based primer of your choice that will prime and seal knots.
2 – I tend to spot fill nail holes in the moulding/profile sections of architraves and skirting boards with a hard stopper filler and sand with 180 grade abranet with a delta sander for minimum damage. (Jack Pauhl has a great list of options for filling nail holes – materials and techniques.)
3 – Gesso is smooth but gritty, runny but heavy bodied. Similar to Weathershield masonry paint in texture? As an idea of coverage on 5″ ogee/torus architrave or tops of skirtings, 2 brushloads layed on evenly will do a 10-12″ section of primed moulding. Leave one hour to dry, and repeat. Leave overnight, sand with 180 grade abranet. You have a really tough flexible base on which to apply subsequent coats of paint.
So in a couple of days, 2 guys can prepare and finish a lot of trim to the highest standard.
If you want to apply gesso really fast, or the grain is really pronounced and requires several layers till the grain disappears, you can succeed in a realistic timescale by spraying on the filler. I have had good success with a compressor driven Sata 100 B-P HVLP and a 2.5mm tip. Very little overspray. Demoed for me by Alasdair of Flints Theatrical Chandlers.
The options are endless with a pressure pot attachment, you can gesso larger areas too!
Surface filler for flat areas
In addition to gesso on mouldings you have to do some filling and sanding on the flat areas to ensure a solid blemish free base for acrylic top coats. Rather than pick and choose what to fill, I skim over the “flats” on baseboard completely with something like Toupret 110 “polyfiller”. Zinsser Ready Patch would give good results. 2 skims are better than one. I use a flexible 2″ steel filling knife, and sand with 180 abranet, using an orbital sander or a rectangular abranet sanding block – both attached to a vacuum of course.
With the surfaces all filled and sanded, and in good shape, I caulk joints, and apply either 2 coats of top coat, sanding between coats, or maybe a tinted primer undercoat plus top coats. It is very nice, and each stage goes pretty quick – but it’s just 7 or 8 stages to a finish!
Ordinarily, if you use standard low VOC low odour water-based paint systems on less than perfect woodwork, you need to down grade your expectations on the final finish, because compared to oil paints, even the best water-based primer/undercoats and top coats just don’t have enough body to fill surface imperfections. Generally, they look OK at first glance, but on grainy surfaces up close they tend to look a bit “skinny”.
But sometimes needs must, and you have to deliver 5 star finishes with water based products only. It is possible, and now you can suggest to your discerning clients, the options to go the extra mile with low odour low VOC products.
And if you are one of the many decorators out there feeling bamboozled by what acrylic eggshell or gloss is “best”, why not change the chip a little and try focussing on base coats not top coats. Let your prep do the work, and just find an acrylic eggshell or gloss you like for the way it applies and lays off, colour, availability, and stick with it. And in worse case scenarios, with a drop of floetrol, flop it on, as Aggie says, and it will look great!
Please bear in mind that water-borne paints (hybrids with oil/water mix) will behave more like an oil paint. You still need a solid base to work from though, because flatter primers do tend to suck the life out of topcoats. We should have some good new info to share on primers/topcoats compatibility soon.
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