Polyurethene disaster almost made me cry

[Rob D]

 

Codensed story. Job to make long bar type shelves that join together. 2.4m long 3" thick and heavy. Resin filled any holes which took ages. Finally finished and one last coat of thick polyurethene on top...

 

 

.... and the stuff wouldn't go hard. Could scratch my nails through it after 3 days. I think a combo of thick coat and cold night...

 

Had to sand all 4 boards down (took twice as long as kept gumming the papers up) and re treat (with a different varnish).

 

Very painful lesson indeed....

[Big J]

Painful! Sanding varnish is like sanding green timber - the sand paper lasts about 15 seconds.

 

I'm trying to figure out the timber - is that some of my elm?

[Rob D]

Yep some of those very first 3" elm planks.

 

 

They look good now but it's taken a lot of 'character' to soldier on and re do them... prob a good 8 hours....

 

 

Ah well.

[Big J]

A lost day like that can be heart breaking.

 

They will look lovely in the end though. The difficulty with the polyurethene was due to damp and cold?

[tommer9]

Ew- nasty Rob. What a nightmare. Beautiful timber all the same.

[Rob D]

I think it was down to thick coat and low temperature.

 

 

What was more gutting was when I got to the 4th board it had hardened a bit more overnight in the kiln.... would they have dried with time?

 

Dunno.... but a lesson to myself in that I need a proper area to dry things in.

 

I'll put some pics up when they're (hopefully) all finished!

[tommer9]

Thick coat and cold are not condusive to PU drying rob. Warm/ hot environment is good IME, and as you say, a thick coat of that stuff will take along time to dry off. Its pretty gloopy isnt it?

[Rob D]

Yes it's quite gloopy but can give a nice sealed finish good for wiping etc...

 

 

I'll know for next time at least just what you need for the elboes is another load of unnecessary sanding!

[Timmy C]

I have always used this AC1 ACID CAT SYSTEM winter and summer, works great and is very hard wearing suitable for anything from bar tops to tables. Also is very clear so does not tint the colour of the timber, though can be pigmented. Available to order from many finishing suppliers and is good value.

[TrollSpiel]

I have little experience with brushed finishes (I spray) presuming you are doing that? But putting on a thick coat without letting the coats underneath really cure, can turn the whole thing to mush. A bit like when you try and put on another coat of gloss / eggshell before the previous is fully cured.

 

I use a PU that is touch dry in an hour, no matter how thick I plough the stuff on - but then it is always in the warm.

 

Morrells 440 is a good acid cat.