Ripples in PolyU Finish subcoats

[Tegmark]

I have a problem with oil based PolyU, which in this particular case was applied thick out of the can with fine varnish brush 3". Although each coat was applied & dried very smooth & the final finished surface from polishing is mirror flat. When viewing from one axis (the one that's perpendicular to the brushing) it looks ripply like the light is being bent giving the impression the surface is ripply. The ripples seem to coincide with the brush strokes & direction & are about 1" apart from the next ripple. Has anyone had this kind of a problem? All I know is the issue is under the top layer within the thick film itself. And no amount of sanding will fix it unless a complete redo.

Just want to know what caused this? After all many other surfaces that were done the same don't look like this. Sorry I couldn't take a photo, it proved impossible for me to capture the problem with my camera.

thanks

[Tahlee]

Hi Tegmark,

Could it be from the overlapping strokes of the brush? We know that when poly is applied it tend to ""level out"" of its own accord.. but what would happen if that leveling out process were interrupted.

For example ... where one stoke has been applied ... nearly dries ... and then a second pass makes the drying poly respond to the fibres on the brush

Call it a "design feature"and bask in the wonder of how it was done.


Regards


Rob

[Arron]

Is it possible it's figure in the timber which you are seeing?

[Tegmark]

Hi Tegmark,

Could it be from the overlapping strokes of the brush? We know that when poly is applied it tend to ""level out"" of its own accord.. but what would happen if that leveling out process were interrupted.

For example ... where one stoke has been applied ... nearly dries ... and then a second pass makes the drying poly respond to the fibres on the brush

Call it a "design feature"and bask in the wonder of how it was done.


Regards


Rob

Hi,

I don't think this is it, I applied the coats very quickly & they levelled out very flat before it started to set. After it was touch dry it looked pretty flat, but maybe with alot of coats & the solvents can do something to pervious coat?

[Tegmark]

Is it possible it's figure in the timber which you are seeing?

Not sure how to really tell tbh. Maybe the wood warped up a tiny bit or soemthing?

[dinosour]

Have you tried talking to manufacturer re problem. Some of their tech lines are very helpful.
As an aside I had issues using polyu, when applied with a brush it left a lot of high points which did not sand out between coats, this was on a pine desk top. I had to make a second top and tried applying the polyu with a long nap 150 mm roller, admittedly it was a satin finish but what a difference I was very pleased with the result and it's now my choice method of applying polyu.
Hope you find and share an answer with us.

[Tegmark]

This also happens with 2pack PolyU. Just to be clear it's not the surface, but inside the overall film.

Here are some small vids so you can see what I mean, even though the cam quality is not too good the problem is still visible.

The 1st vid shows when looking with the grain & along the same axis as the brushing was done. The reflections look like what you would expect a perfect flat surface to look like.


The 2nd vid shows looking against the axis of the brushing direction & you can see the reflections look ripply, like as if the surface was ripply, but its flat & smooth. This is more noticeable when polished up.

My guess is this is probably caused by the bristles & with many thick coats somehow causing the light to bend & distort.

[ian]

i'm thinking that the "thick" coats you've been applying are way too thick.

do you have any way of measuring how thick the coats are?

[Tegmark]

i'm thinking that the "thick" coats you've been applying are way too thick.

do you have any way of measuring how thick the coats are?

No way to be sure in my position, if the wood was vertical there would be major runs to say the least, but it's difficult to brush on a thin coat & getting it to spread easy plus you have to be quick as this stuff sets quickly meaning you can't brush it out without leaving brush strokes. Brushing thin just takes too long getting it perfect.

I will try another test piece with actually thinned coats & see if this happens. Might start at 5-10% thinners.


edit: But I still believe this is primarily happening because of the brushing action & no so much being soo thick.

thanks