Primer paint substitute?

I am painting the floorboards of my outdoor (covered) front porch. I want to put a primer coat on first.


In the past, indoors, I have successfully used old white paint as a ';primer'; coat.


I have lots of white indoor latex paint left over from a previous job and I thought I might use it as ';primer'; for the outside job.


Will this be successful?Primer paint substitute?
No, you would be better off buying real primer. Especially when painting floorboards. Paint and primer have two different purposes. Primer is to seal and bond, creating a surface for the paint. The paint is meant to cover.





Would you notice the difference immediately if you used old latex paint instead of primer? No. But you will in a year or two when you have to repaint.





And interior latex shouldn't be used on an outdoor porch, even if it's covered. The paint will be exposed to more moisture and a larger range of temperatures outdoors then it would indoors.Primer paint substitute?
Hey Joe...I live in Central America and guess what. They only sell one kind of paint and it is labeled for interior or exterior. Kinda made me begin to wonder - what is the difference between the two? Well, I don't know the answer and unless you want to keep the porch the same color for the next 16 years - go for it! Just be certain to clean the porch really good. I would use vinegar and water, as vinegar cuts through the crude.





Hope this helps.
Indoor paint is for painting indoor surfaces. Exterior paint is for exterior surfaces ~ covered or not. It's not a good idea to try to cut corners by mixing the two. It's well worth the few extra bucks to purchase another gallon of the proper primer.