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Started a new exterior single story residential house with painted clapboards that needed a lot of scraping. My normal process is scrape, sand, low pressure wash, caulk, light finish scrape & prime, paint x2. I'm a solo part time operator. The issue is I'm ready to prime and the non loose paint left from the first scrape and sand is coming up. It's now loose. I'm attributing that to the fact it has been exposed for a few weeks. It has rained a lot during the time. The wet boards released the previously stuck paint. Can that be? I hope I'm explaining it right. The boards are still slightly wet and not fully dry and I'm hoping once it fully dries the paint might not be loose. If I didn't wash the house I could prime right after to seal the bare wood. Is washing the house that integral part of the process? Granted the north side should always be done to kill the algae and moss.
 

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Started a new exterior single story residential house with painted clapboards that needed a lot of scraping. My normal process is scrape, sand, low pressure wash, caulk, light finish scrape & prime, paint x2. I'm a solo part time operator. The issue is I'm ready to prime and the non loose paint left from the first scrape and sand is coming up. It's now loose. I'm attributing that to the fact it has been exposed for a few weeks. It has rained a lot during the time. The wet boards released the previously stuck paint. Can that be? I hope I'm explaining it right. The boards are still slightly wet and not fully dry and I'm hoping once it fully dries the paint might not be loose. If I didn't wash the house I could prime right after to seal the bare wood. Is washing the house that integral part of the process? Granted the north side should always be done to kill the algae and moss.
( The water can definitely force any semi-loose paint off the surface. I pressure wash before scraping for that reason. )

1. Pressure Wash - cleans the dust film for better adhesion, also treat for mildew at that time.

2. Dry - Must allow siding to dry before priming (I generally return between 10 days to 2 weeks) to start scraping.

3. Scrape

4. Prime

5. Caulk

6. Paint
 

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When I prep old flaking junk like that, I go all the way to prime all in one pass. Wash everything down first and let it dry as Holland mentioned. Once dry, for each area, get your easily/safely reachable work space whether on foot or ladder. Scrape, sand, prime everything you can reach safely. Move to the next section. It not only helps to seal things down and prevent further flaking, but it's just more efficient. Minimum ladder sets and movement.

You obviously can't do it that way for the topcoats as it'll flash like crazy. And I also always prime before caulk. You don't want the substrate sucking moisture from the caulk which can mess with proper cure.
 

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Discussion Starter · #4 ·
( The water can definitely force any semi-loose paint off the surface. I pressure wash before scraping for that reason. )

1. Pressure Wash - cleans the dust film for better adhesion, also treat for mildew at that time.

2. Dry - Must allow siding to dry before priming (I generally return between 10 days to 2 weeks) to start scraping.

3. Scrape

4. Prime

5. Caulk

6. Paint
I shouldn't worry about the dust generated from the scraping and sanding process weakening the primer/paint I'm putting down? I think having a dust free canvas would be best. Maybe that is an opinion rather then a truth.

I went around at different spots and measured for moisture. The spots without paint was mostly under 10%. The spots still covered by paint was over 15%. Is that normal? So I can't seal it up till the painted areas are under 14% correct?
 

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I think it's great you're using a moisture meter to confirm whether or not the substrate is fit for painting. Under 15% MC is typically the norm for exterior wood, depending upon a number of variables.

On a side note, I could think of no benefit to wash the home after scraping and sanding. Seems like it would prolong the job by having to start scraping & sanding, then wash, then allow to dry back out, then return to commence with work. Most homes I've done which require that much scraping & sanding are lead-based jobs, so complete containment is required. Included with containment is removing the sanding dust, which is swept, vacuumed & wiped clean after each section is scraped & sanded. If removing sanding dust is your main reason for wanting to wash after scraping & sanding, it could be done with brooms, rags & vacuums during the scraping & sanding phase. Pre-'78 homes, I could end up getting in quite a bit of trouble by rinsing lead dust from the home after scraping & sanding, (unless all ground & rinse-water were contained, which would be a logistical nightmare).

Even on post-'78 homes, washing after scraping & sanding could more easily introduce water/moisture behind the siding and other areas you wouldn't want it to go. As far as order of operations for the job, it certainly varies, depending upon any number of variables, as well as the overall scope of work. One thing that never varies, for me anyways, is the washing, which is always done first, (only exceptions is if tree & bush trimming are required before washing in order to gain complete access to all substrates).
 

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I usually power wash a week before. Then come back and scrape/sand, and prime all at the same time, like Joe67. That way it keeps moister/weather out of what I have scraped. After that caulk & paint.
 

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Discussion Starter · #7 ·
Thank you all. I just didn't want to get any contaminates in the newly applied primer and paint. Live and learn. It will certainly decrease production time washing then scrape&sand&prime then paintx2. Now if it will just stop raining!
 

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Thank you all. I just didn't want to get any contaminates in the newly applied primer and paint. Live and learn. It will certainly decrease production time washing then scrape&sand&prime then paintx2. Now if it will just stop raining!
How so? I think most painters would agree to the contrary. You wash and return to do the job once siding is dry. In what ways would scrape, sand, wash, wait for it to dry, then return to commence increase production time?
 

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I shouldn't worry about the dust generated from the scraping and sanding process weakening the primer/paint I'm putting down? I think having a dust free canvas would be best. Maybe that is an opinion rather then a truth.
If youre worried about it, give it a wipe with a dust brush or rag before priming. Its certainly not something Ive ever concerned myself with. Theres generally not a whole hell of a lot of dust created on outside preps. I guess if you were hitting it with an orbital, it might be a different story, but I would just blow the dust off with a leaf blower or something. if that were the case.
 

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Discussion Starter · #11 ·
How so? I think most painters would agree to the contrary. You wash and return to do the job once siding is dry. In what ways would scrape, sand, wash, wait for it to dry, then return to commence increase production time?
I must have not made myself clear. You are right. washing first then scrape sand and prime decreases production time. It will take me less time to get the job done. It makes sense now. Before I was thinking of the all the dust and lingering paint chips. Also of treating the newly exposed wood and opening it up to better accept the primer. It is my opinion the brightening the exposed wood open the grains to allow more primer in. Is that correct? I use a solution of 1 cup oxalic acid powder to 5 gallons of water. I spray it on after I washed the house (bleach/soap mixture) wait 10 or 15 minutes and rinse.
 

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I must have not made myself clear. You are right. washing first then scrape sand and prime decreases production time. It will take me less time to get the job done. It makes sense now. Before I was thinking of the all the dust and lingering paint chips. Also of treating the newly exposed wood and opening it up to better accept the primer. It is my opinion the brightening the exposed wood open the grains to allow more primer in. Is that correct? I use a solution of 1 cup oxalic acid powder to 5 gallons of water. I spray it on after I washed the house (bleach/soap mixture) wait 10 or 15 minutes and rinse.
I've never once used oxalic on paint-grade wood, but your ratio is so diluted that it wouldn't have any ill-effects on the wood anyways, unless maybe you didn't pre-wet or you didn't rinse thoroughly afterwards, (which I highly doubt). Oxalic can be safely applied at a rate of nearly 10 times stronger than what you applied, so I don't think it was the cause.

The only scenario I can think of where oxalic would be appropriate for paint-grade wood might be if you were doing a home with tannin-rich wood and you were concerned about tannin-bleed through your topcoat, or maybe on a home where the fasteners where showing signs of rust-bleed. In addition to brightening wood and helping to restore nominal pH levels after cleaning products with high alkalinity are applied, oxalic is great at removing tannin and mineral stains. Beyond that, I'd never consider using oxalic on homes to be prepped for paint. A thorough rinsing of your bleach/soap mixture will be more than sufficient on paint-grade homes as long as you pre-wet, keep wet, and thoroughly rinse afterwards.

If you were using oxalic to open the pores of the wood on the areas you've sanded to raw wood, the same could be accomplished by using straight water on a damp microfiber cloth during the dusting/cleaning phase. Water opens up the pores of the wood extremely well. It's actually a technique that's been used by finishers for many years, (called "water-popping", which is typically done before staining to help mitigate blotchiness.
 

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My exterior painting process is the same as Holland's. Pressure washing after scraping will almost always ensure more peeling paint because the moisture will continue to undercut the existing paint.

One method to address the dust, would be to blow it down with one of those battery operated leaf blowers. I haven't done this, but I'm sure it beats a dust brush.
 

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I use the OPs method (scrape/sand, then wash) due to the massive number of chips that go flying when you pressure wash a house like that before scraping. How do all you wash-it-first types contain chips, especially on lead jobs?

I do find that there is often some (minimal) additional scraping to do after washing, but I always figure it's an area that wasn't noticed on the first go-around.

As far as the workflow goes, I will sometimes wash each side right as I finish prep (before moving on to the next) so it will have time to dry out while I prep the other sides. I haven't found a full week dry time to be necessary in my climate (Northwest United States)--usually two to three days is sufficient.
 

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I use the OPs method (scrape/sand, then wash) due to the massive number of chips that go flying when you pressure wash a house like that before scraping. How do all you wash-it-first types contain chips, especially on lead jobs?

I do find that there is often some (minimal) additional scraping to do after washing, but I always figure it's an area that wasn't noticed on the first go-around.

As far as the workflow goes, I will sometimes wash each side right as I finish prep (before moving on to the next) so it will have time to dry out while I prep the other sides. I haven't found a full week dry time to be necessary in my climate (Northwest United States)--usually two to three days is sufficient.
You can buy oversized pressure washing tips that will allow you to still have the full flow capabilities of your pressure washer, but at a fraction of the pressure. I can wash with one of my 3,500 psi rigs at 600 psi with the proper tip. All I do is refer to a pressure washing nozzle chart, find the desired PSI I I'd like to wash with, follow that number to the column closest to the GPM of the rig I'm using, at it gives me the exact nozzle.

People often try to adjust their unloader on their pressure washer to increase/decrease pressure, but doing so will also decrease your GPM's, and when it comes to cleaning efficiency, it's all about the Gallons Per Minute. The unloader really should only be set once and then left alone.

Many others will just buy a set of 5 tips from Home Depot and maybe use the white one to keep pressure low. Problem is, those store-bought tips are pre-calibrated for a specific machine running at a specific PSI and GPM. Unless your rig matches those specs exactly, the results will be inconsistent.
 

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I use the OPs method (scrape/sand, then wash) due to the massive number of chips that go flying when you pressure wash a house like that before scraping. How do all you wash-it-first types contain chips, especially on lead jobs?

I do find that there is often some (minimal) additional scraping to do after washing, but I always figure it's an area that wasn't noticed on the first go-around.

As far as the workflow goes, I will sometimes wash each side right as I finish prep (before moving on to the next) so it will have time to dry out while I prep the other sides. I haven't found a full week dry time to be necessary in my climate (Northwest United States)--usually two to three days is sufficient.
Something similar to Eagle Tarps, or landscape matting that allows water to flow through while trapping paint chips. It can be used with, or without a water containment system.
 

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Something similar to Eagle Tarps, or landscape matting that allows water to flow through while trapping paint chips. It can be used with, or without a water containment system.
If it is lead-based you are not allowed to pressure wash.

Lead safety states that you must tarp with plastic and collect/discard all paint chips on a daily basis.

*I never pressure wash with the intention of removing paint chips. We always "soft wash" to treat mildew and to help remove dust film. We prefer to remove paint with a scraper only.
 

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If it is lead-based you are not allowed to pressure wash.

Lead safety states that you must tarp with plastic and collect/discard all paint chips on a daily basis.

*I never pressure wash with the intention of removing paint chips. We always "soft wash" to treat mildew and to help remove dust film. We prefer to remove paint with a scraper only.
So, there is no water washing even if you contain the run off? As far as pressure washing with the intention of removing paint, I never thought it was a good idea. Especially on wood. On the other hand, I've used Roto tips on coatings over steel with decent results. Especially, where abrasive blasting was out of the question.
 

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So, there is no water washing even if you contain the run off? As far as pressure washing with the intention of removing paint, I never thought it was a good idea. Especially on wood. On the other hand, I've used Roto tips on coatings over steel with decent results. Especially, where abrasive blasting was out of the question.
I believe current lead-safe regulations state that pressure washing is not allowed, but I’ve always understood that to mean with the intention of removing paint.
 

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If it is lead-based you are not allowed to pressure wash.
You are allowed to use a pressure washer to wash pre-'78 homes, provided you're not "disturbing" the surface, and for exteriors, that's defined as 20 sq. ft. This subject has been discussed here a number of times. The real sticky area is when must waste water be contained, and realistically, HOW. My approach has been to wash at the lowest possible pressure required in order to be effective, but without risking removal. Washing from a safe distance and with a pressure of 500-900psi on homes with peeling paint works for me. Diverting wastewater via berms & socks to grass or dirt in order to prevent it from running down the driveway and into the sewers has kept me out of hot water thus far, but there is still much ambiguity on how to deal with wastewater, and exactly when you must do so.

The EPA makes no distinction on collecting wastewater from hand-washing a lead home and using a pressure washer.

...From the RRP Rule, "Projects that do not disturb a painted surface are not subject to the RRP Rule"
...From a EPA FAQ Checklist, "Answer: Low pressure washing can be used to clean a child-occupied, pre-1978 school as long as it doesn't disturb paint"
 
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