You must use a bonding primer like Zinsser's products, Fresh Start at BM or Bonding Primer at SW. Michael

Getting Great Stuff foam off your hands can be challenging, but here are a few methods you can try: Use soap and water: Try washing your hands with soap and water, as this may be enough to remove the foam. Use warm water and lather your hands with soap, then scrub the foam off your skin. Use acetone or nail polish remover: Acetone can dissolve Great Stuff foam. Apply some acetone or nail polish remover to a cloth or cotton ball and rub it onto the foam residue on your hands. Be sure to wash your hands thoroughly with soap and water after using acetone. Use a pumice stone: A pumice stone can help scrub the foam off your hands. Wet the stone and rub it over the foam residue in a circular motion. This may take some time, but it can be effective.

Were the stools to be left natural,the gap would be a problem. Since they appear unfinished,I asume they are to be painted which will "almost"conceal the misfit. Having said that,much depends on who's at fault here. If the same contractor installed new windows,I would expect near perfect fit and finish. Lack of attention to detail while installing window make's trim out difficult. Actualy the root could lie with framing and/or siding. It's not unusual to find different depths from window to window. The solution is to rip off a strip at rear of stool equal to gap.

Hi, I am in the middle of painting my oak cabinets. The prep is long and grueling..but worth it. I used a product called Pore-o-Pac, oil based. It is a brush on wood grain filler. Very time consuming, did 2 coats on each door front (not the backs) and all the cabinet frames. You cannot see the grain through the paint. This is what I did: Sanded the surfaces with 180 sandpaper, washed with TSP. Let dry thoroughly (and then a little longer)...Then painted the grain filler on. (My little trick is to buy an empty one gallon container, dump the qt size grain filler can into it. This way you can stir it up very nicely. You can thin this product with mineral spirits.) You leave it on for a few minutes, then use the scraper to scrape across the grain at a 45 degree angle. Next it says to wipe it off in the direction of the grain lightly (I guess so as to not pull it out of the grain). Let it dry for 24 hours. Then, if you really want to hide that grain..do it a 2nd time. I even did 3 coats on 2 doors that were very heavily grained. Also, as you are scraping it off, I would just dump it back into my container, if the product started to get too thick--just add the mineral spirits! It does take a long time, but really--no grain! Oh yeah, another little tip: The ends of my cabinets are laminate--the fake wood to look like the grain. I used a product that is a primer for painting over plastic. I got it at Lowe's, it is their brand--sort of like the Krylon Fusion, but it was a clear primer. After I sealed off the area where there would be overspray, I just followed the directions, and then I was able to follow it with the primer I used on the cabinets! So far so good. Make sure there is plenty of ventilation!!!!! As I mentioned up above, I bought 2 quarts of this stuff, it really goes a long way. Good luck! Here is a link that might be useful: Pore-o-Pac