Problem with stains on new nitrocellulose topcoat

[graham.murfett]

G'day all
I recently manufactured a wall unit for a customer, and finished with Mirotone 3125 primer and 3150/60 semi gloss topcoat. White.
Came up nice, customer happy. Get paid.
Then i get a phone call, customer placed TV & stand on bench of wall unit, which has left 18mm round yellowish stains from the softish round rubber feet under the TV stand. Some devil chemical reaction has occurred.
So, I now have a new ongoing hell trying to make stains disappear/go away/get out of my life, as the wall unit is now plastered into place in situ. So I can't remove bench and respray. This isn't going well so far...

My question...
If I had put a clear coat on top of the bench area, would this have stopped the leaching into the white?
I am prompted by some comments made by Woodpixel about auto clear top coats in another thread.
Hopefully someone has been through this hell as well and has some advice.

[woodPixel]

ah look! Im mentioned!

I was just doing a search for MDF and painting (Im playing again with finishes! Again!) and was having outstanding success with Haymes Prepcoat Elite (Tricoat).

With rubber, I have found the stuff coming out of China is causing an orange like stain on a number of finishes. Its leeches out! Even neoprene based table cloths. This has been shown to be true with an number of feet I use for chopping boards, even from different makers. Nobody, it seems, sells real rubber any more.

I'm surprised it had a reaction with Mirotone 3150 however. That stuff dries like diamond.

With finishes, if I get a troubling surface and want super dooper resistance - I've found a new product that Im currently really enjoying - https://www.autorepairsdirect.com.au...oat-500ml.html

Both Mirotone and AutoRepairsDirect give excellent advice. Id ring mirotone first and show then a picture - they'll probably be pretty upset!

It isnt acid catalysed, but gee-whiz is it hard. It is seemingly impervious to everything.

[graham.murfett]

G'day Woodpixel
I rang Mirotone. They told me what I already knew. Chemical reaction between synthetic rubber & 3150.
I'll be more instructive with future customers.
This stuff never used to happen.
Thanks for the link.

[graham.murfett]

Woodpixel

Re the Haymes Prepcoat Elite (Tricoat),
What size needle are you using to spray it? 2.0 or 2.5!?
Are you using a flow cup to get consistent thinning prior to spray? https://www.autorepairsdirect.com.au...up-ford-4.html
How many seconds to empty?

Thanks

[woodPixel]

Easy!

I mix exactly 1L of Floetrol to 10L of Tricoat. Zero buggering around.

The Floetrol comes from The Paint Place (because they are a small biz and Non Evil) but this is the stuff: https://www.bunnings.com.au/flood-4l...ioner_p1563340

The Floetrol adds just the right consistency and does and AWESOME job on levelling, flattening and slowing the dry just goldilocks. As I said, I just mix it to 10%, straight into the can! I used to use a flow cup (Ford) which is a Wagner one, but not any more.

For the guns - I paint with 1.4, 1.7 and 2.0 depending on the days heat. When its ~25°C I use the 1.7 (its my favourite gun). Hotter I use the 1.4. When its 10° to 15° I use the 2.0, but most of the time I'll just stick with the 1.7.... check for tipping occasionally, especially on hotter days. I spray outside in a marquee.

I regulate to 75psi at the compressor. For HVLP that's bloody high, but I trim that at the gun with the lower air volume knob. I use about an 8cm fan held at 10cm using a medium speed with an 1/3rd overlapped wet edge.

I'll test on cardboard to ensure the settings are right first.

For HVLP I'm doing everything against all advice I'd normally give! If I were asked, I'd say: #4 Ford cup flowing to 40 seconds, use ~30psi, a 50% overlap, wet edged and held at 20cm on a fat wide fan... but...

When I first started, I used to thin the Tricoat down to do this with just water, but I found it too.... watery.... and took too long to dry. Humidity also made it an absolute bugger (if it was later in the arvo towards dusk and humidity raised, the Tricoat would re-saturate!) I also didn't like the way it sat so flat so fast. Haymes say to thin no more than 10%... but to get it to flow to 40 seconds, one must dilute to 25%.

Butttttt, I like to jam the paint into all the nooks and crannies and tend to lay it on a bit thick. After a billion jobs using Haymes, my "rules" works well for me.

I always do three coats. First is a tack, let it dry maybe 5 minutes, then two fat coats about 20 mins apart (despite Haymes' instructions). Attached is a picture of the three coats and how they look. It dries very predictably.

If I need to fill, I do a fat tack coat, let it dry an hour, then use Timbermate (I wet it up a bit so its "juicy") and run that in all the MDFs edges. If its a big job, I'll use Gyprock Ultra-Top Finish Coat. Its suuuuper smooth and dries fast. It sands velvet smooth too, but its its an OUTSIDE job, for its as dusty as hell. Sand with 180. I use the Mirka Ceros and Abranet 180 for that, rather than the Festool ETS150/5 as it gives a smoother finish.

Sand the edges manually. I use a bit of 180 stuck to a rod of thick MDF. I get super smooth finished edges like that. Good control too. If you use the electric sander you'll obliterate the detail in milliseconds. I blow all the dust over to the neighbours using a small air nozzle

Sometimes I'll do another mist coat, re-fill any last errors, sand and do the three coats. I don't bother sanding between coats, just at the end.

Here are some pictures done just this weekend (30° @ 60% humidity). Final coating is Haymes oils... another rant though, but it shows the end result is pretty schmicko.

Undercoating, layers 1, 2 and 3.... and after drying prior to sanding.....
MDF 3 coats undercoat.jpg MDF undercoated.jpg

After sanding and shooting on two thin coats of oil (Haymes).

steps sample 3.jpg steps sample 2.jpg steps sample 1-1.jpg

[aussiepens]

You could possibly try a rubber (french polish) with nitro thinners to polish the stain out. Experiment on a sample first.

[woodPixel]

I found a great chart for using the Ford #4 velocity cup: zahn #2 Ford #4 Viscosity Charts

PDF of the page is attached in case website goes up in magic smoke. PDF and zipped HTML with images. I stripped out all the cruft and left pure info.

zahn #2 Ford #4 Viscosity Charts.pdf

zahn #2 Ford #4 Viscosity Charts.zip

and some of the images that may prove useful.....

various Ford Cup timings.PNG viscosity4.jpg viscositychart.jpg ViscosityKrebs.jpg

[graham.murfett]

Thanks for all the info WoodPixel

All your paint advice mkes sense. Thanks again, for the photos & charts etc.