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How hard/resistant should precat be?11/21/19
I know my question may be hard to answer but I will try my best to describe it how I test hardness/resistance
My product of comparison is a floor polyurethane varnish (non catalysed, hardware store type). Now even if the look may have been "ok" the resistance was phenomenal! To scratch to the finish bare wood I would need a penny and press real hard. I suppose this is what you would expect for a floor polyurethane
I have now switched to a precat lacquer(duracoat precat from mohawk). I knew it would be less scratch resistant that poly but I am confused as to whether is supposed to be THAT MUCH less resistant.
I first tried self sealing (all products are from mohawk) :
this has left me a fantastic look but a light scratch with my nail(without denting the wood) would remove all the finish up to the dye/first washcoat easily. Some people have pointed to me that the pigment stain could be the problem as self sealing on natural has given me better result.
So I decided to go with the recommended vinyl sealer :
(Havent completed the next steps but they will go as follow)
Up to the grain filler step I got a big improvement on resistance. In order to lift the vinyl sealer I must scratch to the point where I dent the wood and if the wood is too hard then I won't be able to lift the vinyl without scratching a lot. I estimate I must use about 100% more pressure to damage the vinyl. I am now waiting for the grain filler to dry (oïl) before applying the lacquer coats. I went ''by the book" using the recommended products on the tech sheets.
For those who have experience with precat "how" would you describe it's resistance/hardness. Whats considered acceptable. How can I stain wood if finish can't stick to it. Does mineral spirits/solvent from grain filler damage the vinyl?
This is standardized as taber abrasion.
It's not always published but all the manufacturers test it and should know it.
The short answer is: Pre-cat is usually pretty horrible, even after final cure time (IE 30 days).
This is compared to what you compare it to - polyurethane.
(post-cat CV/etc is much better)
This isn't me being judgey - only you can decide where the tradeoff is for your customers.
But pre-cat is very much meant as a time/cost saver, not as an ideal finish.
thanks a lot daniel.
I think this answer my question very well fortunatly my work is mostly decorative light use furniture. up to now the resistance I have is as you describe not horrible but not fantastic either. for decorwtive woodworking it fits the bill.
But Ill probable switch to CV if I ever need to do a heavy duty furniture(i.e. customers with kids :))
Did you try your finish schedule without the pigment stain? You don't say if it's oil-based, but if it is, it's a likely culprit. Oil-based stains require days to dry fully and the problem is worsened if you don't wipe it off aggressively.
The stain is Indeed Something I will try. I use mohawk wiping stain which is supposed to be ready to top coat after 30min but I suppose this is in summer heat
I also Apply it after a washcoat to minimize blotching but I have limited experience with them. Is it how pros usually do it? Do I need to Apply it to bare wood (over the dye)? Should I scuff sand it to remove the binder and help the vinyl sealer stick to the wood/wascoat?
So I have completed the test pieces. THe grain filler has cured and put on another full coat of vinyl sealer than full coat of precat. It's been now 24+ hours and the pieces seems to have become more fragile (same as selfsealing precat) but some spots are more resistant than others wich raises the Following question:
-Have I applied too thick of a finish (Vinyl washcoat + vinyl full coat + grain fille + vinyl full coat + lacquer full coat + sometimes even toners)? I Don't have specialized equipement to measure but since it seems the more coats I Added the more fragile it became maybe I applied the finish too thick (4-5 tho is damn thin if you look at a feeler gauge and it's easy to go overboard). I know about the crazing and all but could this be an early symptom?
- Have I recoated too soon or too late? My vinyl spec sheets ask for a 45min dry time than scuff sand but isn't catalysed and mention no recoat window. I may wait a few hours to a full 48h depending on my Schedule. Since It need sanding I also assume that sealers don't "burn in".
My bets are on the finish being too thick. I have a test piece wich I did not liked the color so ended up stopping spraying after only 1 vinyl coat and guess what...they were damn hard to scratch
To tack on to what i said earlier:
Scratching is a resistance issue, but it could also be adhesion.
If you want to know if you have adhesion issues, do cross-hatch testing of various schedules and thicknesses.
That will give you a clear and concrete answer as to whether it's adhesion or fragileness or something else, and is easy to do with tape and a box cutter ;)
Thanks for your answer Daniel,
Remade 2 test pieces from ash. Since the wiping stain (or the stain being over a washcoat) is likely the culprit I will try 2 Schedule.
-Both will have a black dye stain (wich is in fact really dark redish)
I stained directly over the Dye on the first one. Blotched a bit but the also hid the red tint of the dye quite well. Hope it did note lift too much of the dye (acetone based)
The second one was stained after a washcoat. It was very uniform but kept a black redish tint (will need a green toner).
Althout this wiping stain is supposed to be ready to topcoat in 30min (well according to the spec sheet) i will give it 72h to dry.
as of now the only difference I see is that the stain over the wascoat still ooze oil from ash pores and the smell scream mineral spirits. As for the stain on bare wood the smell is already almost gone.
Although is is not specified in the spec sheets I suspected the 30min dry time may be for an application over bare closed pore wood.
Anyway I will take these at home for 72h and continue the Schedule. If the wiping stain did not cure over the washcoat after that I gess I will have to trade a bit of blotchiness for a more durable finish.
You must stay in the manufacturers specification for film thickness. It's as simple as getting a wet film thickness "comb". Less than $2.
Your comparison is not really fair. You used a floor poly. Designed to be tough. It can be put on pretty thick. It’s a durable(soft) finish. You are comparing it to a thin film hard(brittle) cabinet finish. Not really apples to apples.
You’ve compounded the issue by putting down various other products under it. The one thing that stood out was your sanding schedule. It should be 240grit after grain filler. 320 between topcoats. If you are looking for max durability you would do 3 topcoats. 600grit is a no go with solvent based products.
Adam you pointed Something I may have overlooked. I come from a waterbased finish background and, unfortunatly, had to learn all by myself.
My reasonning behind using such high grit was to prevent sanding trought the top coat and since lacquer burn in it would not cause trouble. Right know I Don't think intercoat adhesion is my problem since the finish seems to lift up to the wiping stain but I will try using no higher than 320 on my last 2 samples in order to maxime adhesion.
As for the comparison yeah I know it's a bit unfair. I knew lacquer wood be less resitant but I was a bit skeptical that it would be that much fragile. I mean I can lift it after a week using only a finger nail.
I had sprayed regular nitro on a decorative box (bare wood) a year ago (first time) and in my memory, the regular nitro, although less resistant than poly, still needed a bit of effort to lift from the wood. As it is know, I can wash my pieces with water without problem but using a penny I can remove the finish just like a lottery ticket.
You can see 240 scratches in white paint and clear topcoats. 320 is invisible. No reason to go higher because you will potentially lose adhesion.
You should ask your rep if their precat actually has burnin. That’s an old school laquer thing. The reality is you are sanding to remove defects, dust, runs between coats not simply for adhesion.
we started using milesi 2k poly on tabletops and found it so nice to use we put it on everything now, no mo lacquer. it doubled our Finishing material costs but saves work, improves throughput and best of all the shop is happier, less headache. we thin it more than recommended because we don't want a built up look but that takes some of its strength away.
resurecting and old thread but to help other I think have solved my problem.
After dozen of test pieces I have figured that I was spraying my coats too dry and also too thin. I got a wet coat gauge (man it's hard to mesure a non colored finish!) and found out that I was spraying coats that were barely 1mil thick whereas the manufacturer recommand 3-4mil thick coats.They seemed wet in look but hazed in about 30 sec whereas now they dry in about 5-10 min to the touch like the pds sheet states.
I also switched to a "post-cat" (not your typical post-cat since you add the catalyser to the whole gallon which last for 6 month) lacquer (mohawk versalac) wich is supposed to be more durable than a precat.
Although I know It won't beat CV or the brushing floor poly I was used to, I am really satisfied since I use it for decorative furnitures that won't see a lot of abuse.
Hope This can help anyone reading the thread