View Full Version : Poly, varnish gloss vanishing during cure
03-06-2002, 11:35 AM
I have had problems with several coats of Goldspar polyurethane varnish loosing its gloss during the cure from tacky to cure. Finish is left with existing heat in building at night. I will turn temporary propane blowing heater on again in morning. Heater sits in window and draws supply from outside. Temp recorder never drops below 50'. Humidity around 35% - 40%. Does not allways happen. Gloss goes within min. of this. Is it moving air? New oxygen? Warm air?. Out side humidty within 5% of inside. Any thoughts?
03-06-2002, 11:47 AM
I've had problems when the temperature drops a lot between application and cure. As long it cures to touch before the drop in temperature, there's no problem. I've varnished successfully in a cold winter garage and on a hot summer day. Sounds like you apply the varnish in a warm room and then let it cure while the temp drops. Try applying the varnish early in the morning when the building first reaches its daytime temperature. Don't use the propane heater. Rely only on the building heat.
03-06-2002, 01:45 PM
Tommy how are you? The clear poly? used to varnish? this is my understanding of your question. Put me back on track if I'm wrong.
The variables that effect the paint surface type, 'gloss', are consistent through all glossy media.
These can be numerous. Gloss reaches it's highest level of fineness if the underlying surface is smooth, then deteriorates, if underlying surface types are rougher than smooth. Finishing grits like 400 and 600 will allow the highest quality surface type, using 120 less gloss. 1200 grit will cut and polish paint to glossy, if not glassy.
Clear Poly is my favourite (this year). I use a sander sealer to sit the grain down, and keep it down. After two coats sanded or woolled back, a smooth surface. With all the inherant beauty of the wood retained. A uniform surface.
Secondly, Poly skins quickly, perhaps not giving you the surface smoothness that shows gloss off to it's best advantage. You no longer have a gloss surface you have a stippled surface. Less glossy. 2 strokes maximum (for me) for poly the third one ruins my surfaces. Do not over stroke 'this' paint. This is possibly the problem Skipper. Practice reducing your number of strokes.
There's a potential thesis in all question about varnish. Very popular topic in WBF.
Thirdly, dilution can affect the draw of the paint, a rougher delivery, less gloss. Consider doing tests with a flow control medium, for use with water based paints. I like to dilute Poly paint to maximum dilution with water (I do not dilute Enamel heavily it kills the gloss), I like to paint thinly, many layers. The greater the quality of your application, spray on highest quality, finger painting lowest quality or quality brush vrs an ordinary brush. This could be the other main contributing factor Skipper.
If you are using an additive, is it compatible? to retain gloss. It doesn't have to be an anti skid additive, it can even be a micro balloon.
Make sure your 'cross linker' is at the right dilution, this is difficult to calculate. Worth a second look always. This changes things greatly.
The lighting that you view the boat in can affect gloss, and can show overstroking, all the highs, lows and semi-glosses.
Edit: I agree fully with Scott, temp is every thing with this paint. Try starting with a moist sponge before dipping it into the paint and wash it every 5 minutes or put that one in water and use a second moist sponge, then repeat. Try this if it suits.
[ 03-06-2002, 09:29 PM: Message edited by: Wild Wassa ]
03-06-2002, 08:05 PM
Tommy, I just had a good look at the boats that are in various stages of being painted with poly.
Although we are not using the same manufacturer's products they have close to the same qualities, no doubt.
None of the surfaces are highly glossed. They are all of a semi-gloss, but still glossy. I wonder if you might be expecting an Enamel gloss surface. Which our paint doesn't show.
Another point that surprised me was the number of areas that were dissimilar in their gloss types due to the different paint thicknesses. We just haven't put enough paint on yet. Could this be the same in your case. If you paint thinly, this could be a possibility.
There is one deck that has been rolled, and is a fine lustered surface, satin, bearing little resemblance to gloss. Could you have used a small roller.
I hope this extra backup helps.
Back again, the data sheet for my CLEAR poly states; All characteristic qualities are acheived at 20 oC only. This paint is designed to give a natural timber lustre. BETTER LATE THAN NEVER.
[ 03-06-2002, 10:57 PM: Message edited by: Wild Wassa ]
03-06-2002, 10:38 PM
I should have written on two different coats. The sheen is very high gloss, but it turns to a very dull sheen (as if sanded with 400 grit) in different areas on the same piece of material. All areas are being wiped down with the same solvent and tacked with same type of tack rag.
03-07-2002, 07:28 PM
Tommy, The problems and remedies are also consistant with Goldspar. Gas heaters will build up humidity and the rapid cooling will give condensation deposits on smoother surfaces. That is more than likely, your problem. I notice a temp drop of about 18 oF in your studio at night if the day temp is about 68-70oF
A copy of this thread has been sent to Yacht Paint's (International in Aust.) Peter Nicholson at his request, this interests him as well. Peter said he would give feed back if he spots or thinks of anything else.
[ 03-07-2002, 09:30 PM: Message edited by: Wild Wassa ]
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