How do you get dried polyurethane off? Soak the dried polyurethane using mineral spirits or acetone. You could also try using the soy-based polyurethane stripper or vegetable oil. Apply either of these products over the dry varnish; let it soften for a while, and then wipe it off.
If you used the brush for water-based polyurethane, you don't need to clean it with paint thinner. Instead, all you'll need is clean water and regular dish soap. For oil-based polyurethane brush, dip it in mineral spirits or turpentine.
Mineral spirits will not affect polyurethane, so a rejuvenator is needed for this. This is simply paint stripper thinned with solvent. It will soften the polyurethane so some of the top material can be wiped off.
The strength means that acetone can damage or remove most paints and finishes, so you should avoid using this solvent as a cleaner on all but the most solvent-resistant finishes. These would include conversion varnish, two-part polyurethane, UV-cured finish and epoxy resin.
Note: You could use paint thinner or even lacquer thinner for this cleaning process if that's all you have on hand, however sometimes they can strip the brush and damage it, so I'd recommend sticking with mineral spirits when possible.
Cleaning water-based polyurethane brushes can only be done with clean water as well as soap. Mineral spirits should be used to clean oil-based polyurethane brushes. You can then buff the polyurethane brush under running water (and soap) with an nylon brush before washing.
Let it soak between coats.
Use a kebab skewer through the handle to avoid bending the bristles. When you're done with the brush, rinse it a couple of times in used mineral spirits, then pure mineral spirits, removing the bulk of the solvent on newspaper each time.
Synthetic bristle brushes are the most common option. The bristles are made with synthetic material, like nylon or polyester, which is better for applying water-based polyurethane. These brushes are also frequently used with latex-based paints.
Mineral spirits are simply a type of paint thinner, mineral spirits paint thinner has characteristics that distinguish it from other products such as turpentine or acetone. Unfortunately paint thinner is used on labels that are referring to mineral spirits in a less refined form.
If you don't like using strong chemicals on your wooden products, you can use vinegar and baking soda to remove polyurethane.
Yes, you can sand off polyurethane. Although using sandpaper solely will not work to remove polyurethane, you can use it at the end to remove any residual polyurethane from the wood. You can use 120-grit sandpaper or 150-grit sandpaper to remove it from the wood.
It quickly removes latex and oil-based paint, polyurethane, epoxy, varnish and shellac from wood, metal and masonry surfaces.
Is turpentine and mineral spirits the same thing? No. Turpentine is distilled from pine trees while mineral spirits (or white spirits) are made from petroleum.
Step 5: Wash the Brush with Soap and Water
I like to use dish soap at this point, because it breaks down the remaining mineral spirits, and doesn't feel quite as oily. What is this? The soap and water should rinse out any remaining mineral spirits or product.
Turpentine has more solvency than mineral spirits. Care should be taken when using it to thin oil- or alkyd-based paints; otherwise the paint could be overthinned, which can cause it to run or drip. Even though turpentine is less toxic than petroleum-based solvents, it can still cause an allergic reaction.
Yes, polyurethane provides a protective layer on hardwood (as well as furniture) making it harder for water to penetrate into the wood. But, it is not waterproof; rather, it's water resistant.
You can, however, use denatured alcohol to remove latex, lacquer, shellac and polyurethane finishes, as it is less toxic than paint strippers, although it may take more time to work than paint strippers.
Generally it is hard to dissolve polyurethane as swelling is the common phenomenon observed. May be you can try with mixture of dichloromethane, dimethyl formamide and methanol .
To create your remover, you need to mix denatured alcohol with lacquer thinner. You can mix them with a stick. This combination is excellent for stripping polyurethane. It is also great because it removes the varnish only, but it isn't harmful to the wood.