# Pressure wash: before or after sanding?



## SkinnyAdam (Feb 21, 2013)

I have always done my pressure wash first thing, waited a few days and returned to the home to begin prep. I've heard other guys say they scrape and sand first, then wash. 

I generate a lot of dust during sanding and I'm worried that my horse-hair brush isn't doing the job of removing it all before I prime. I'm curious how you guys do it? If you don't pressure wash first, what else do you do before pressure washing?


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## Monstertruck (Oct 26, 2013)

Wash first unless it's a strip job.
Don't want to mash any of the dirt into the remaining finish.
Yes, removing the dust after sanding takes some effort.


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## Wildbill7145 (Apr 30, 2014)

I honestly don't think it's possible to remove all debris from a deck in a single bulk attempt. Every time you step off the deck and back on, you're going to be bringing more debris into the situation. Any wind doesn't help either.

I usually do one thorough pass with a heavy duty shop vac and get absolutely as much as I can. After that, it's a dust as you go situation with a rag sweeping anything you find away from the wet product until you're done. It's not a perfect method, but in exterior situations there's rarely a perfect method.

Nature's gonna nature.


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## MIZZOU (Nov 18, 2012)

If need be, we pack along the air hose during priming. Big compressor stays in the van and 200' of air hose comes out.


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## doctors11 (May 17, 2010)

Blow off first with leaf blower. Spread chemicals, scrub, pressure wash. Let dry. Sand with attached vac if needed. Use shop vac with floor attachment (with bristles) to vac up dust then blow off again with leaf blower. Occasionally I'll follow with a barely damp rag (water or mineral spirits...depending).


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## doctors11 (May 17, 2010)

The only time I'll scrape first is if i's a badly peeling solid stain. I want to expose as much bare wood as possible before spreading chems. I explain to customer that after washing I'll need to scrape again, and sand, as the washing will lift the edges of the existing stain.


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## SkinnyAdam (Feb 21, 2013)

I'm talking full exteriors


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## CApainter (Jun 29, 2007)

SSPC (Society for Protective Coatings) standards suggest washing certain surfaces first so you don't introduce oils and other grime into the existing paint film by sanding, as has been mentioned. Particularly if most of the existing coating will remain.

Of course major dust from subsequent sanding will have to be removed by means of a blower, vacuum, or dusting. If time permitted, I wouldn't be opposed to a quick second wash down. But from experience, I learned that sometimes a second wash can cause further lifting or cracking of paint during the drying process.

Provided there isn't a huge amount of dust, I like the leaf blower method the best. I happen to occasionally use a cordless Black and Decker.


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## mudbone (Dec 26, 2011)

CApainter said:


> SSPC (Society for Protective Coatings) standards suggest washing certain surfaces first so you don't introduce oils and other grime into the existing paint film by sanding, as has been mentioned. Particularly if most of the existing coating will remain.
> 
> Of course major dust from subsequent sanding will have to be removed by means of a blower, vacuum, or dusting. If time permitted, I wouldn't be opposed to a quick second wash down. But from experience, I learned that sometimes a second wash can cause further lifting or cracking of paint during the drying process.
> 
> Provided there isn't a huge amount of dust, I like the leaf blower method the best. I happen to occasionally use a cordless Black and Decker.


Agree! Thats why when Im prepping siding I only do enough of it in a day so I can also get it sealed before I leave for the day so during the evening no moisture of its kind can enter it.


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## Slopmeyer (Aug 2, 2009)

spot priming as you go I feel is best. Then if its really that bad a simple rinse with the hose will suffice.


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## CApainter (Jun 29, 2007)

mudbone said:


> Agree! Thats why when Im prepping siding I only do enough of it in a day so I can also get it sealed before I leave for the day so during the evening no moisture of its kind can enter it.


That's a really good practice. When I'm prepping anything that exposes a bare iron substrate, I'll make it a point to wrap up the prep and get a coat on what I've prepped before the end of the day. Even though many of the newer coatings will claim to go over mild rust.


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## Gough (Nov 24, 2010)

CApainter said:


> That's a really good practice. When I'm prepping anything that exposes a bare iron substrate, I'll make it a point to wrap up the prep and get a coat on what I've prepped before the end of the day. Even though many of the newer coatings will claim to go over mild rust.


::thumbsup:

We did a cast-iron store front and were following right behind the sandblaster. You could see rust starting within a few minutes after blasting.


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## journeymanPainter (Feb 26, 2014)

Gough said:


> ::thumbsup:
> 
> We did a cast-iron store front and were following right behind the sandblaster. You could see rust starting within a few minutes after blasting.


That more common than you think. Depending on what your painting though a white blast might give you a little bit more time over a brush blast


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