Estimaing Program making my own

Wolverine said:

Any liquid covers 1604 square feet per WET mil per gallon... WET... So to figure out how much paint you need for 'dry mil thickness' you would:

1604*% Solids= # of square feet per DRY mil per gallon...

So if your paint is 50% solids...

1604*0.50= 802 ft2 per DRY mil per gallon

Click to expand...

Wolverine,

I like numbers, and I find this interesting.

I tested this on a few SW products. ProMar 200 interior latex is speced at 42% solids, 1.6 mil DFT, and coverage of 350 to 400 sf. Using your formula (1604*.42)/1.6 I came up with 421 sf. Exterior SuperPaint gave me (1604*.35)/1.44, which resulted in coverage of 389 sf.

I would think that if I worked backwards I would get to the 1604 number. Using the mid range on coverage, I usedthis formula for PM: (375/.5)*1.6 and would come up with 1429. With SuperPaint I come up with 1542.

Just so you don't think I'm being a jerk, I really do find this interesting. But the numbers aren't working for me, so I'm wondering what I'm missing.

It could be that the formula is a general guideline, but the difference between PM and SP is about 8%, which seems significant to me. And neither is real close to the 1604 number you cited.

Perhaps of greater interest is why the solids would be higher for an interior paint. Is it in the expectation that only 1 coat would be applied, while with an exterior paint the expectation is 2 coats?

I don't see an immediate reason to know this, but I have long believed that the more I know about the products we apply, the better I can serve my customers. It also helps me understand why one product is better than another in a particular situation. So I am all eyes.

Brian Phillips

It's because SW is EVIL... EVIL I say! :yes:

Brian, it is because the numbers that you are using are nice round guesses that SW comes up with. They figure the coverage based on the solids (Volume Solids) and then they take in to account how much paint will be wasted on a roller and in a tray and they spit out a number. So, that coverage they list is not perfect.

The formulation I gave is 'the' exact theoretical coverage. You have to watch out for volume solids vs. weight solids and wet mils vs. dry mils. Of course, with 100% solids materials wet solids IS dry solids.

Last, many times the solids listed on the datasheet is kinda like the EPA fuel rating on a new car. It's off...

Oh yeah... as far as the solids are concerned of the interrior vs. the exterrior... there are just too many factors to discuss. It's almost like trying to figure out why someone planted geraniums instead of daisies.

However, in general... <--- in general... if you were to make 2 different paints with the same resin (1 interrior and one exterrior)... and all other things were equal... it would be wise to add more fillers to the interrior to increase the scrubability... The problem with making a more specific statement is that many properties are resin specific. In other words, you could have 2 resins that give the same look and gloss but one of them dries harder than the other. That would also contribute to scrubability.

This could go on and on... most formuations are a delicate balance of materials that derive the desired properties...