[PSDkevin]

I have no experience with water based poly so forgive my ignorance. I decided to try it on a project and really like the drying time and how quick it lays out on the surface. The problem came after 4 coats. I wanted to smooth out some spots so i went to lightly sand with 220 and immediately went right through the stain and all. It had sat for about 30 hours or so. So the only thing I can think of is that the coats are really thin or it didn't cure long enough. I brushed it on because i couldn't get an acceptable spray with my equipment.

Any thoughts?

 

[cabinetman]

WB poly finishes best by spraying. If you experiment with your spray setup you should be able to get good results. As for your problem, you likely didn't have enough build. If the undercoats weren't fully cured, it wouldn't sand properly.

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[Steve Neul]

I have no experience with water based poly so forgive my ignorance. I decided to try it on a project and really like the drying time and how quick it lays out on the surface. The problem came after 4 coats. I wanted to smooth out some spots so i went to lightly sand with 220 and immediately went right through the stain and all. It had sat for about 30 hours or so. So the only thing I can think of is that the coats are really thin or it didn't cure long enough. I brushed it on because i couldn't get an acceptable spray with my equipment.

Any thoughts?

My experience with water based poly is it takes 4 coats to equal 1 of other finishes so you probably just didn't have enough. When you do sand you have to be careful just how much you sand. It would have been better to just very lightly scuff over it with 320 grit paper after each coat then to put 4 coats on and then try more agressive sanding.

From where you are the easiest fix would be to chemically strip the entire area where you sanded through the finish. It's more work and takes much more skill to try to touch it up then to strip. When you are applying the finish it's more important to give it a good drying time between coats then to wait 30 hours before sanding. Just go by the label instructions and give it much more time if the weather is especially humid or in winter close to 50 degrees.

You should have been able to spray the finish. It sounds like the sprayer needs a thorough cleaning. From time to time you have to completely take them apart clean them. What kind of sprayer do you have?

 

[WillemJM]

Which brand of WB did you use?

 

[HowardAcheson]

As others have said, waterborne poly creates a very thin film. Because it it fast drying, brushing can be problematic. If you plan to rub out (sand) the finish you must ensure that you have built up a thick enough film to prevent sand through. Get your sprayer cleaned or fixed. Spraying is the best way to apply a waterborne finish to a flat surface.

I have found it best to use 320 paper for between coat sanding and 400 through 1200 grit paper for creating a satin final finish. You need to also mount your paper on a rigid flat sanding block with a felt or rubber surface. Then apply very light pressure.

 

[PSDkevin]

I am going to purchase an earlex to spray this stuff soon but just haven't pulled the trigger. I used a borrowed HF hvlp. The compressor driven one. so I don't discount that it might need some cleaning. I have a regular spray gun and some experience with it. To me the orifice is the wrong size for spraying This but I'm certainly no expert.

I used rustoleum brand. I live in a small town and it's all that was on the shelf. It seems more of an application problem than a product problem.