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layers of polyurethane not bonding

I used Minwax high build poly on sanded, 100 year old 1/4" thick red pine floors. we sanded, vaccummed, tacked with mineral spirits and put on the first coat at 2pm sunday. 4am Monday we started buffing with what we thought was the correct pad to texture the surface sufficiently for the second coat to stick. I used a square buffer with a red pad, which had a hard time staying on the buffer to start with.

I checked and it it seemed like the buffer was doing something but not much. Honestly my gut told me that it wasn't enough, but I thought that since we only gave the poly 12 hours to dry, we were still working with partially wet poly and it should bond well.

So we buffed the floor and tacked again. Then we put on a second coat, which was definitely thicker than the first (most of which was absorbed into the wood). so by 8am Monday it was all on. We let it dry 24 hours before walking on it and then let it dry till Thursday evening before placing anything on it for an extended period of time.

You might already know the rest. The top layer easily shifts and moves against the first coat and can still easily be dented with my fingernail. Wherever we put something down, it leaves a mark and if I peel up the second coat a bit on a spot, it comes away in a layer, showing that there is not a good bond with the first coat. When I dig at it a bit with my fingernail, I find that it is still a bit tacky to the touch.

We realized that it was only about 55-60 degrees in the house while the poly was drying, so we put on the heat and have been keeping it at 68 for the past 24 hours, starting at 6pm Thursday. This morning (Friday), it's still soft and peels.

I'm afraid that I've already diagnosed my problem and am left with the obvious solution: mechanically strip the top coat and sand with 150-180 to prepare whatever is solid and dry, then recoat with a thinner coat and give it plenty of dry time. Any other ideas out there? Any tricks to get a thick coat of poly to dry? we got the high-build poly so I wasn't as anal about keeping it really thin.

We might just use it as is for now, so furniture and cleaning and walking will rip up the top coat, instead of us having to do it.

thanks for the feedback

Re: layers of polyurethane not bonding

we sanded the original floor well. I can't find a spot where all of the poly is coming up, just the top coat. even though the boards were cupped, we made sure we hit everywhere there was old shellac. The first coat soaked in well and made a great bond with the wood. It's this top coat that's peeling away. I hope the higher temp and some time will at least help it set up completely, even if it's not fully bonded to the first coat. Thanks for the help.

We used oil-based Minwax high-build from Home Despot. About 4 gal total for two coats on 650 sq ft.

Re: layers of polyurethane not bonding

I ain't no painter but 4 gal for 650 sq/ft sounds like a ton!

How is coverage listed on the can?

Re: layers of polyurethane not bonding

Coverage is rated at 800-1000sq ft./ 2.5 gal and we got 1300 out of 4 gal, which is fair I guess because we threw out 4 soaked sheep skin applicators worth and def didn't use the last few cups at the bottom of the first can, which had gotten some debris in it. I know coverage is usually in perfect conditions and we had huge gaps in the wood and only sanded down to 100 grit.

The areas where we were thick is definitely a larger problem then the really thinly coated sections, but even those aren't bonding well enough. It looks great, but I think we'll have to redo it within a couple years to clean up the mess we created with the poor sanding job between coats.

floor problems
Re: layers of polyurethane not bonding

Having the same problem with the same product. I waited 36 hours between coats and it is not bonding. Top coat can be torn up with a fingernail. I am afraid I am going to have to remove the top coat because even after 8 days it is not hard. ANy help would be appreciated.

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