Primer is designed to stick to stuff. So when you drop some on your laminate floor and it dries, you've got a problem, but not an insurmountable one. You can remove primer from wood by sanding it, but the surface of laminate flooring isn't wood, and if you sand it, you'll ruin it. Scraping isn't going to work either, so that leaves only chemical approaches.
Matt the Painter doesn't recommend using paint thinner or mineral spirits to remove paint from a floor, mostly because of the fumes. If you aren't overly sensitive to volatile organic compounds, solvents like these might be a good option. However, there is a better cleaning solution that you can make yourself that will probably get the job done without giving you a headache. If it doesn't, you can graduate to stronger chemicals, including acetone and, yes, paint thinner, if necessary.
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A Homemade Cleaning Solution
The safe way to remove water- or oil-based primer from a laminate floor is to use a solution made with these ingredients:
- rubbing alcohol
- dish soap
Mix the water, alcohol and vinegar in more-or-less equal portions — perhaps adding a bit more alcohol for stains that have been stepped on and ground into the finish — and add a few drops of dish soap. The mixture should get sudsy when you stir it.
Vacuum dirt from around the area from which you need to remove the primer to make sure you don't grind any of it into the finish when you rub the spot. Using a soft cloth dampened with the cleaning solution, rub the paint until it loosens its grip and comes off. To avoid leaving streaks, rub in the direction of the wood grain.
Stronger Chemical Paint Remover
Ammonia is an emulsifying agent that is particularly effective for removing water-based paint and primer, but it can damage the finish, so you must use it with caution. Rather than mixing an ammonia-based cleaner with water, it's easier to just use ammonia-based window cleaner. Spray it directly on the paint stain and rub immediately with a soft cloth.
If you don't have any luck with the window cleaner, it's time to graduate to a stronger solvent, but here you run the risk of damaging the finish if you choose the solvents indiscriminately. Acetone is a strong solvent that dissolves paint, but it won't affect the cured finish on laminate flooring. You probably have acetone somewhere because it's the main ingredient in most nail polish removers. Dampen a cloth and rub with the grain of the flooring to remove primer stains that other cleaning solutions can't get up.
Last Resort — Paint Thinner
If you attack a primer stain with the homemade cleaning solution, followed by window cleaner and acetone, there's little chance it will survive. On the off chance it does, paint thinner or mineral spirits are your last resort. Open the window to ventilate the room and wear a respirator, if necessary, then dampen a cloth and rub with the grain. If you aren't sensitive to fumes, you might consider beginning with this solvent and save yourself the time of trying the alternatives.
A really stubborn stain might survive even this treatment, but not if you apply heat to soften the binders holding the primer to the floor finish. Dampen a towel, place it over the stain and place an iron set to low heat on top. Wait about 30 seconds, moving the iron to avoid scorching the towel, then rub the primer with paint thinner while it's still warm.