Polyurathanes - are they mostly the same?

Hi All,
I've done a quite a few Jarrah projects over the years, with finishing being Estapol Sanding Sealer, sand, Estapol Sanding Sealer, sand, Estapol Satin x 2 (from spray pack). The result was consistent.

My first project (two 400 x 350mm tables) now since Bunnings stopped selling Wattyl products so I ended up with Feast Watson Sanding Sealer and Cabothane Satin spray pack. I have been trying to finish them for the last 3 weeks. Issues have been bubbling of the topcoat and sanding back and recoating resulting in visible areas of opaqueness where the old top coat feathered back to the sanding sealer, almost like the adhesion of the top coat was poor and the feathered areas slightly lifted.

In trying to work out why the issues are arising I thought I would ask if there is a known difference between the Wattyl products and what I am currently using? It then comes down to temp/humidity issues (being winter in Perth) or something like the rags I used to wipe up after sanding are contaminated.

I had an issue with Cabothane satin spray cans a couple of months ago. I was spraying what was to be the final coat, at about midnight late April. It wasn't that cold, probably around 10°C. But within 45 minutes as the finish began to dry and shrink, it lifted off the surface. I was finishing multiple items and the finish lifted badly on one item, and a minor amount on the another. My guess was that it was too cold to begin with, and I had only very lightly scuff sanded between coats using worn 400grit to remove dust nibs and nothing more. I probably would have got away with it if I was a little more aggressive with the scuff sanding or spent some money and ran a heater in the garage for an hour or two before and after spraying.
Attachment 438036

That looks similar to what I experience and I would have thought temp was about 16C when the top coat was applied. In my case when going over it with a random orbit and 240 grit the feathered edge would look like that and I could keep sanding and the feathered edge would retreat across the surface looking like that.

I do know that some clear sprays will not cure properly if it's too cold; they should say a minimum cure temp on the can, it's often 20 degrees. Mirotone Spraylac seems to be much better behaved in the cold.

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Originally Posted by elanjacobs

Mirotone spraylac seems to be much better behaved in the cold.

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mirocat pc 3220 ?

I've been looking into investing in the range of Mirotone products.

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Originally Posted by woodPixel

mirocat pc 3220 ?

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No. It's called Spraylac

Mirotone is a very well known Australian specialist industrial coatings company that has been a major supplier of wood coatings for many years. Spraylac 1012 is an aerosol lacquer mostly used for small touch up applications . I would expect being a very low solids material due to the aerosol pack and using Dimethyl ether as the propellant it would be easy to have issues especially in lower temperatures. I use Mirocat 3220/60 which I spray with a HVLP spray gun over Mirocat 3244 sealer. This week I spayed some blackwood furniture without issues at 10-12 degrees C which did surprise me as many other similar coatings do have issues at lower temperatures. I have found the Mirocat 3220 one of the best products to use as it has high solids and excellent sprayability with very good flow and levelling and certainly works for me in a smaller home workshop. I have been in larger furniture plants were the temperatures are closely controlled during application and drying and also use heated spray systems to enable high quality faster production. Clearly the small hobbyist/woodworker can not replicate that system but with careful selection of products and procedures it is possible to get good outcomes. Cheers, Paintman

I've used Spraylac in high single digit temperatures without any problems :shrug: