How to be good at spray foam
This is what iv learned doing mine the past few days. They are in order
1: clean the surface until the rag comes off white. My bus is from the desert, and it was loaded with fine brown dust on every horizontal surface inside the walls. You donít want the foam sticking to that instead of the metal. I wiped every wall and ceiling with wet rags until it was clean, vacuuming the heavy stuff first.
2: keep the temperature exactly right for the foam bottles and within range for the surface youíre spraying on. You can change the temperature easily by putting them in a sink of hot or cold water and shaking them every few minutes. It could take all day to heat them up by putting them in a warm room. My foam said 75 degrees for maximum coverage, so I made them 77 in the sink. That way rather than being 75 at the beginning and cooler at the end, they passed through 75 while I was in the middle of spraying thus keeping it as close to ideal temperature for the entire time. You can use an ir thermometer to tell, I prefer that to the temperature strip on the tank. The surface temperature that you spray on is slightly less important as the foam heats up as it cures, but you want to be as close as you can to what the instructions say. It is a lot harder to change the temperature of the bus than it is of the tanks.
3: use foam it green or have a helper watch the hoses at the tanks for air coming out. Small bubbles are okay but stop when it looks like the first picture. With foam it green, the two parts are yellow and blue so when one stops you will know right away. When mixed properly it is a very light green color. If you use a different kind, have someone watch the hoses for air bubbles coming out of the tanks when theyíre almost empty so you know when to stop before making off ratio foam. Keeping the temperature exact, both will have air bubbles in the lines at the same time if youíre lucky.
4: have the best lighting possible, not blue leds. This is not as important if youíre using all yellow foam (you will have to know when to stop by watching the hoses for air instead) but the foam it green color change is not huge, and you might not notice if the lighting isnít great. See the second picture, note the light blue on the left side. I scraped it off before finishing. With good lighting you will know right away. I got some white led work lights at walmart for cheap and hung them up in the ceiling of the bus. They shine down below the windows, so for doing the ceiling I moved them to the floor shining up and covered them with clear plastic.
5: use the fan tips everywhere. Coming out of just the mixing nozzle, it comes out too fast to control easily for good coverage. Once I put on the fan tip, it was much more even. You will have to move much slower than without it because the foam is spraying over a much wider area. Even in the corners itís still better, and because itís thin you can shoot it in narrow gaps like I have around my windows. In the third picture, you can see above the back window before I switched to the fan tip and it is much more uneven, compared to the surface in the second picture. Those pipes have the wires for the marker lights in them, I pulled out all the wires and labeled every one so I can put them back. Donít bury wires or anything else in the foam that you might need to work on at any time in the future.
6: use slow rise behind the chair rail. It sprays out of the nozzle the same as the regular foam, but you can connect a tube to the end to stick it down in the bottom. I ran out of slow rise with two sections left to do so I sprayed the regular in them. It worked for two but for 20 I would buy the small slow rise kit.
7: donít remove the floor until after you spray foam, unless you expect to need to do a lot of welding to it. Itís easier to remove the floor with the drips on it than it is to scrape foam off of your nice repainted metal floor or have to mask it all off. I didnít mask the chair rail either, the foam will be removed from there with a wire wheel. I will post about removing the excess later as I need to get more foam first, but donít use a hot wire cutter as it will produce cyanide gas.
8: donít bother doing a ton of math to find out how much you need. I bought two 600 board foot kits and 200 of slow rise for my 40 foot rear engine bus at first, and I am seeing for myself how far each kit goes. There are too many variables to get it right the first time especially with a large bus, and you will need to order more anyway.
There are plenty of arguments for or against spray foam which we have all seen before, but this is just my experience. Itís expensive, perhaps 5 times more expensive than some options, but 10 times better. It is a mess, but mask everything and get one of those harbor freight painting suits with the hoodie hood and itís really not bad. Thereís not overspray like paint, it falls out of the air right away. Itís really easy to do your own spray foam. I have never done it before, but after figuring out the fan tips it looks like a pro job (or better, pro to me means fast&cheap) and I know there are no gaps or places missed or off ratio because I did it myself and didnít rush. Anyone can be good at spray foam if you follow the instructions, take it slow and observe how itís going on. All you have to lose are mixing nozzles and you are given a lot of them for a reason