[mrcleanr6]

i usually sand everything dry as primer is porus and will soak up moisture. plus wet is such a mess. either way it shouldn't be taking that long and 220 scratches should come right out with 400 in no time. i have used duopnt uro primer once before and i thought it sanded easily. not sure what the problem is but i would try dry sanding with 400 and a 3m or equivelant soft block. is it possible that you are getting dirt under you 400 wetpaper and its causing scratches as you sand??

[crashtech]

Here's a thread that talks about 3M dry guide coat. It is excellent for use between grits to ensure that you are removing all the scratches from the previous grit.

Also, I would consider 400 to be a bit coarse for final finishing, in either dry or wet-or-dry paper. In my shop we use either 500 dry or 600 wet or finer for topcoating. It's better to go a bit too fine than to see the scratches in the finish!

[Scode68]

These scratches have been there since after using the 220. Other wise the 400 seems to be polishing the primer and it has somewhat of a shine.

[Scode68]

Originally Posted by crashtech

Here's a thread that talks about 3M dry guide coat. It is excellent for use between grits to ensure that you are removing all the scratches from the previous grit.

Sounds like good stuff but the URO 1107 is a very dark gray (almost black) so it’s not going to work for me. I’m going to re-shoot another coat or two of the primer reduced as recommended and give it a go. Maybe I’ll start blocking with 320 this time. By the way I’ve been using this long board that says it uses 2-¾”x17-½” paper along with the appropriate wet or dry paper.

[baddbob]

If you need a guide coat for dark primers just buy an aresol can of $3 automotive lacquer type sandable grey primer and put a light dust coat of that over your Uro. It needs to be really thin so hold the spray can a good distance away and just mist a light coat on. If you're doing a lot of work it's beneficial to have a gallon can of lacquer primer on hand just for use as a guidecoat, most economy lacquer primers can be bought for about $35 per gallon and reduced $150 will give you 2.5 gallons of sprayable guidecoat in black, grey, or red they offer the cheapest avenue for guidecoat. Your board should work just fine. I use the dry guidecoat on light colored primers between sanding grits and for this it works great-no masking! The Uro I used years ago sanded like butter, I can't imagine spending 7+ hours on a roof unless it's a full sized van

[jcclark]

I don't know what brand of sandpaper you're using but if you got
hold of some "el-cheapo" sandpaper you may be working youself
to death for no reason. That happened to me.
Make sure you have a good sandpaper. (just another thought)

[Scode68]

The light colored lacquer is what I’ve been using and the paper was $30 a box so I don’t think it is cheap.

Like I said before about the lighter colored URO compared to the darker. When using the gray (1104) it was easy sanding and since I switched to the dark gray (1107) the primer seems harder.

[jcclark]

Originally Posted by Scode68

Like I said before about the lighter colored URO compared to the darker. When using the gray (1104) it was easy sanding and since I switched to the dark gray (1107) the primer seems harder.

Well something isn't right, I don't think they should be different.
You got something different there, don't know what.
(maybe you need more bourbon??)

[scot]

That white plastic Hutchins sanding board is a Bad Mamma Jamma!
I really like it for final sanding. It's light and has a Pistol Grip handle and knob that's easy to hold onto.
It's bad, bad, and bad!

[chadsbodyshop49119]

Originally Posted by scrot

That white plastic Hutchins sanding board is a Bad Mamma Jamma!
I really like it for final sanding. It's light and has a Pistol Grip handle and knob that's easy to hold onto.
It's bad, bad, and bad!

I'm with this guy..

[Scode68]

Ok, I sprayed it with a further reduced filler primer mix of 4:1:2 (primer:activator:reducer) and there is defiantly less build but it looks like the scratches were filled. I will know better hopefully this afternoon if I get a chance to sand it. Since the primer is dark gray I have been using a light colored lacquer guide coat and that is how I knew that I had a flat surface.

Now for the paper! I was going to start again with 400 dry and then hit it with 600 dry but I think I am going to see how the 600 works first. As far as wet and dry paper goes, is there a difference in the grit? I thought 400 would be 400 regardless. Thought the only difference between the two was that the wet type could handle the water and not lose the aggregate.

[mrcleanr6]

600 dry in my opinion is a losing battle. a couple swipes and its clogged with dust and doesn't work anymore. there is really no reason you cant do 400 dry with a block. you can then lightly go over with 600 wet if you want. if it was me i would get it flat with the 400 and a block then very quickly run over it with a da and a soft pad with 400 to smooth out any uneven scratches and your ready to go. if you spend more than 3 min with the da your overdoing it. da scratches are much smoother than when blocked and if you put a soft pad on it, it will smooth it evenly.

[chadsbodyshop49119]

I feel the same way with 400 and sanding, it clogs to fast.. i don't know how you guys do all your sanding dry... I did one today and it sucked.. although, it's getting painted right now, that's the plus side. no sloppy water everywhere

[roger1]

Originally Posted by chadsbodyshop49119

I feel the same way with 400 and sanding, it clogs to fast.. i don't know how you guys do all your sanding dry... I did one today and it sucked.. although, it's getting painted right now, that's the plus side. no sloppy water everywhere

I have good luck sanding dry with the 400 3M stikit roll paper. I do use a brush on the paper to knock off any loading of dust occasionally.
I think maybe it does make a difference which kind of paper you use. Give that paper a try. I always keep a roll of 180, 320 and 400 on hand. I also have the 3M board that is meant for use on their stikit paper but, it should work with any board.

I agree about the 600. That has to be wet sanded.

[Scode68]

I didn’t get a chance to do anything tonight but maybe tomorrow. I think I remember reading someone saying that they will sand with 400 and then run a gray scotch pad to eliminate any of the 400 scratches. Maybe I’ll try that.