What is the very best way to paint a smooth-star fiberglass exterior door by Therma-Tru? Use alkyd or latex paint?

Questions & AnswersCategory: Fiberglass Door Finishing QuestionsWhat is the very best way to paint a smooth-star fiberglass exterior door by Therma-Tru? Use alkyd or latex paint?
Angie asked 9 years ago

I just bought a brand new smooth-star exterior door from Therma-Tru. The door is for my back-north facing-patio. We live in northern Utah where the weather can literally range 30-40 degrees in one day. The door-for the most part-does not get a lot of direct sun, but it does get hit by wind, rain and snow sometimes.

I do not care how long the process takes I want the door to look really good. I have no problem using oil based paint but I am familiar with latex paints and have used them throughout my home. I will be either brushing or rolling the paint myself. I will not attempt to use a sprayer at this time. The color I have chosen is a soft, muted sage green by Benjamin Moore. I actually purchased a quart of Benjamin Moore Exterior MoorGlo Soft Gloss in the color, but have since questioned if I’d like to go this route.

After buying the paint I realized it was not too smart of me to test the paint colors on the actual door. I went back to ACE Hardware and told them I needed primer to cover the paint…they sold me an alkyd primer (I brought the actual paint with me) and unknowingly I put the primer on the spots where the paint was. It didn’t adhere so I ended up, after waiting at least 10 hrs or so, sanding the entire exterior side of the door. Unfortunately I had also painted the molding around the glass (the door is mostly glass).

So now I’m in a couple predicaments. I’ve sanded off most if not all the factory pre-primer (I think) so the door needs to be primed. I will either have to sand the molding or repaint it with a primer that can cover oil based primer, if I am going to use exterior latex. I am not worried about cost because my ACE is excellent about returns even used items especially since they sold me the wrong product. But I also have a Benjamin Moore specialty store very close to my house as well as a Sherwin Williams Specialty store is close too.

What do you suggest I do? Did I ruin anything sanding the entire door? It doesn’t seem like anything is wrong except it is shinier and smoother now (it had a primed-kind of texture before). I also wiped it down with TSP since sanding it in an attempt to take away some of the ‘glossiness’. So Basically…I guess I’m starting with a bare door with the exception of the oil based primed molding.

6 Answers
Crowder Painting answered.

These are great doors, you will like it! You did nothing wrong. Well, maybe trying the color out on the door. For future reference, brush out a couple of coats on some poster board or stiff cardboard to check out the color.

OK, here we go. I always lightly sand my doors before priming. I want a really smooth surface to start. You did good by sanding and the TSP is a nice touch.

Now you need a good primer. The primer I use is XIM UMA brand? Tintable: Product Number 1106 Water Born, Bonding Primer Sealer. This is a little hard to find for most people. Sherwin Williams should have it, also try your local Benjamin Moore dealer. Another good primer is Zinsser 123. Have the primer tinted to 50-75% of the finish color. All you need is a quart.

I always spray a new door, but brushing and rolling is fine. For the finish you will need a quart of Flotrol (smallest container is a quart), a very good brush and a fine tight weave roller. I would use a mini hot dog roller for this job.

Flotrol is a paint conditioner that slows down the drying of the paint, just enough to lay down on the surface. This will be smoother than straight paint. It doesn't take a large amount to condition your paint, about 1/4-1/2 cup per quart.

Apply the primer and paint in the same manner. With one exception, don't add Flotrol to the primer. Use a little splash of water instead.

Brush the edge of the door first. For the exterior side this will include the hinge edge.

Now for the face. Brush the molding first. Be careful not to leave any heavy edges where the molding meets the door. Once this is done you will work in sections. Start at the top. Cut in next to the molding then roll out the section. Work one side at a time; across the top then down a side, now down the other side and ending with the bottom.

You don't want thick coats. It is better to apply 2-3 thin coats of paint than 1-2 thick ones. For the primer, one coat is enough. Allow the primer to dry overnight before painting.

Anonymous answered.

How to Paint a Therma-Tru Smooth Star Door

I work at Therma-Tru, and we are happy you chose to place our Smooth-Star Entry door on your home. We have some recommendations for you from our Product Support Manager. The old rule of thumb is you can put latex over oil, but you cannot put oil over latex. This is the reason why the oil primer peeled off the latex painted sample areas. Smooth-Star doors do not require a primer before painting, but you can use one if preferred. We do recommend Alkyd base primers, or a primer that is suitable with the paint being used, however it should be applied first on the entire door and then painted with the latex. The "textured" primer you referred to sanding off of the door is not a primer but is actually the texture we put into the fiberglass skin (part of the mold that forms the skin) to help with paint adhesion. Now that it is sanded off and the skin is now smoother and shinier, I am afraid the paint may not adhere as well. We would have recommended to simply finish painting the door with the latex, covering the test spot areas with the finish coat and not to have sanded the skin.

Do not worry though! At this point, we recommend cleaning the door with a soap and water solution, priming it with an alkyd base primer and then painting it with the latex based paint. If you have other questions about Therma-Tru or our products, log on to thermatru.com.

Anonymous answered.

The Therma-Tru guy has it backwards. Oil can always go over latex, but latex cannot go over oil, because oil naturally repels water.

anon e mouse answered.

I’d just like to confirm that the Therma Tru guy got it backwards.  NEVER put latex over oil.  It will blister and you will have a  mess.  Frankly, to be safe, I always put an oil based primer on old paint that I am not certain what it is.  The alkyd (oil) based primer will seal any kind of paint and bond well with latex and you will be fine.  If you are using darker paints, you can even have the primer tinted so the latex covers better.  
Hope that helps 

Renee answered.

The Therma Tru guy is correct. Latex can go over oil but not oil over latex. Latex is less stable and if it fails the oil finish will come up with the latex. To paint over oil; clean, lightly sand down the shiny finish or use a bonding primer. Apply the latex. If the latex blisters it’s because moisture got under the latex finish or the oil finish wasn’t prepped properly before the latex was applied..