We are prepping poorly painted exterior cedar siding. The old paint peels off in sheets. The question we have is... how far down does this surface need to be scraped...does it have to go to raw wood...with no remnants of old paint. This is proving to be extremely labor intensive... but we want a 10 year paint job..so what is needed here..we plan to hand prime with oil based primer when surface is ready..and then coat with 2 coat of acrylic latex..also can we spray the latex after we hand prime. We've had painters say hand paint everything !?