After painting, why do you need to put polyurethane on it? The reason is that it will protect the paint and make it last longer. Now that you know why, how long do you have to wait for the paint to dry before you can apply this protection?
What is Polyurethane?
Polyurethane is a type of super-tough varnish that is formulated so it will bond tightly with another as it dries. It gives off a finish that is more resistant to solvents, abrasions, impacts, and water. There are two different polyurethanes that you can choose from to put over your paint.
- Oil-based—this will turn slightly amber but will form a hard, durable film in a few coats. It dries slowly so there is a wait between coats. This has a stronger scent
- Water-based—this will dry clear and is more watery than oil-based so you will need more coats. It does dry quickly
How Does Polyurethane Protect Paint
It protects your paint by being a highly resistant barrier. It protects it from mud, fungus, rain, dirt, and more. It can even help prevent the color of the paint from fading if it is exposed to a lot of sun. If the wood is not protected it can become dry and listless. It will give your finished piece richness and depth.
The Right way to Polyurethane Over Paint
Step 1: Wash The Area Where You Are Putting The Polyurethane
You need to make sure that all the grease stains, dirt, or any type of filth is washed off before you can put on the polyurethane. To clean the area, use a rag or soft sponge along with a powerful detergent to clean the surface.
Take one-half cup of trisodium phosphate and mix it with warm water. Trisodium phosphate is a blended cleaning product that painters and contractors use to make sure that the surface is clean. You can also just use a powerful detergent such as Tide. This step will help to increase the polyurethane adhesion.
Step 2: Get Rid Of The Scuffs
After the painted surface is dry, use 120-grit sandpaper, and scratch the surface. You want to prevent any deep scratches from forming and flatten out the sheen. If you do not get the deep and/or large scratches out, you will be able to see them under the polyurethane.
In this step, you can use a palm sander or by hand. When you are finished, wipe away the dust with a damp cloth.
Step 3: Oil- Or Water-Based Application
This is when you need to decide which type of polyurethane you are going to use. Do not use a roller to put it on because they tend to leave bubbles behind. You should either spray it on or use a brush. If you decide to spray it on, do not thin it out because this can cause it to excessively run.
- Brush on—this is best when you are working on a flat surface where you need to build up a durable film.
- Spray-on—this is great for hard to reach surfaces like chair spindles or shutter louvers. This will give you a thin film that is not as tough as brush on.
- Wipe-on—this is best for contoured surfaces such as stair balusters and crown molding. They create no drips but they do form a thinner coat so make sure that you use them where wear is not a concern.
Step 4: Apply First Coat And Etch Surface
After you have applied your first coat, let it dry for the time that was listed on the container. Once it has completely dried, you want to again scuff scratch the surface with 120-grit sandpaper.
When you do this, you are removing any small dust particles. You are also flatting and squishing any bubbles that have become hard in the finish.
Step 5: Apply Second Coat
Once you have scuff scrubbed the surface, it is time to apply the second coat. Generally, you will never need more than two coats. Let it dry for at least 24 hours.
How Long for Paint to dry Before Polyurethane
It is important that before you apply polyurethane over the paint that the paint has fully cured. What determines the length of time paint needs to cure will depend on the type of paint that is used and the humidity level. On average, it takes about a week but there are some paints that will only need 24-48 hours. The longer you can wait before you put on the polyurethane, the better.
This means that the solvents have evaporated from your paint coating and leaves the paint feeling dry to the touch but the paint is not 100% dry.
This means that the coat of paint has reached its maximum hardness. It is 100% completely dry.
When putting polyurethane over paint, to get the best results, you should wait until it has cured before doing so.
To see if your paint is dry, lightly touch an inconspicuous area with your finger. If it does not feel tacky, then it is dry. To see if the paint is cured, press your fingernail into the paint and if it leaves an indent, the paint is not completely cured. Your paint is cured if there is no visible indent.
Factors That Affect The Dry Time
Type Of Wood:
Some wood does not cure properly and the reason is that the wood is producing chemicals that will inhibit the crosslinking process. You should try to avoid using some aromatic cedar wood and rosewood as these are two of the woods that have those chemicals.
This is a natural cause that can affect the dry time of the paint. In lower ambient temperatures, the paints will thicken and cause a longer drying time. If it takes too long to dry, the paint can run or start sagging. This means that the paint has created an uneven surface so you will have to redo the paint job. If it is too cold, the life expectancy overall of the paint will reduce.
Type of paint:
There are many varieties of paint and each one has its own drying time. Check the package to see if it states the time. One of the reasons that it is different is the material the paint is made of. It also matters how dark the paint is because the darker the paint, the longer the drying time.
The sheen also matters, such as is it flat, satin, eggshell, hi-gloss, or semi-gloss.
If there is no proper ventilation, then it will take longer to dry. If you are painting in a closed area be sure that it is properly ventilated to increase the drying time. If possible, paint it outdoors because there you will have better ventilation.
When the humidity is high, there is increased water vapor is on surfaces and in the air. Wood is porous and will absorb excess moisture, which will make it hard to paint. The paint could create a bubble or peel off. When it is high, no matter how many coats of paint you put on, the results will be the same
Types of Paint and dry Time
- Latex/water based—it takes about four hours to dry but it is advisable to wait at least 24 hours Cure time 21-30 days
- Oil-based—6-8 hours dry time. Cure time 3-7 days
- Chalk—30-60 minutes but is better to wait 24 hours. Cure time 30 days
- Velvet finishes—this is was made especially for painting on furniture. It will take 8-9 hours to dry.
- Milk—30 minutes but best to wait at least 24 hours. Cure time 30 days.
Always make sure before you use polyurethane on your paint that you have proper ventilation. When putting polyurethane over paint, it is recommended that you use water-based paint. The reason is that some oil-based paints will turn a yellowish color over time if coated with polyurethane.
If you use oil-based polyurethane, it will take about 24 hours for it to be dry and with water-based polyurethane, it should take about six hours but takes about 30 days to fully cure for either type of polyurethane.
As noted in the article, how long for paint to dry before polyurethane, the answer varies. A lot of factors figure in to know the dry time such as type of paint, weather, etc.