Are you sure the "Water Seal" you refer to is an oil based (requiring a petrochemical to clean the brushes and NOT soap and water)? Is it "transparent" and has no color listed or shown on the can? There is no need to "strip" or "sand" the Thompson's Oil based TRANSPARENT Water seal Product because the paraffin soaks into the wood and is not on the surface. It has no pigments in it that rest on top of the wood. Therefore there should be no "peeling" or "chipping" of the surface and no obvious wear other than wear to the wood itself, usually near stairs and door and very slight in most instances. If its the Thompson Oil Based Transparent product you used, there is no need to strip or sand. You may want to clean the surface (IF it is visibly in need of it) with something like diluted Clorox Exterior house cleaner to remove pollen, dust, dirt and any surface mildew (mildew spores are transported by the wind and there is always some on the surface, although it probably hasn't "stuck" to it. Its basically a spray or brush on job and rinse with a garden hose. Let it dry fully for at least a day (two is better). then you can apply your new oil based deck product. I suggest you wait at least one full year for the beading of water to stop and even two years is OK. My front deck got the Thompson's two years ago and I will stain it with an oil based stain this year. It requires minimal cleaning....I may just use a garden hose with a firemen's nozzle. The deck gets full sun all morning so mildew is very hard pressed to survive there. Best stain, IMO are oil based TWP. The main thing to watch for is to avoid "soap and water cleanup" because that is a water based, possibly latex deck product. You wouldn't think to put latex paint on your indoor hardwood. Latex wears like crap to foot traffic. A true stain soaks the color deep into the wood and is not a "paint pigment" that sits on top of the wood. The whole problem with deck preservation has been caused by the VOC controversy which tossed a lot of good products out of the market by legislation. The emphasis on water based products opened the door for a lot of "new" water products with "paint stains" which are not stains at all. Unfortunately, those products require stripping because they wear out fast, leaving some areas bare and have adhesion problems as they age. Stripping is more work than the refinishing. ALWAYS google the Material Safety Data Sheet of the product you are considering so you know exactly what it is. Be careful that most big box stores sales clerks are "selling" what the store has in stock. That is why they get paid. The best products used by Contractors are available through building supply vendors that cater to builders and carpenters and not the general public consumer. They do not refuse to sell to the general public, but "quality" is their life blood, not quantity of sales based on huge purchasing contracts supplying a nationwide chain. Wish you good luck. Don't be swayed by the claims of 6 year and 10 year lifespans. If its a water based paint pigment product, it will look like hell for half of those claimed "lifespans", Most people would prefer a true stain that can be reapplied easily without having to strip the deck. And. if you have to strip the deck, how do you strip the railings and balusters? I've done it....took a pressure washer and two days to complete. Then I started reading and wised up on the number of really crummy products that are available, being pushed by big box stores and consumer agencies that prioritize water based over oil because of an "environmental" bias. The idea behind using an initial Thompson's Oil Based Transparent on a new deck comes from a highly ethical, lifelong contractor/carpenter who needed a workable solution for customers who couldn't decide how they wanted there decks treated during an age of great confusion. The Thompson Transparent has an effective anti-fungal and gives good service up to two years. When you compare to other oil based products costing three times as much, many of them also recommend restaining after two years. BTW, oil based paraffin products do not support fungus.

In my experience, standard oil-modified polyurethane wears better, and it certainly costs a lot less. The downsides are slow drying, smell and ambering. As much as I like oil poly, I feel Weathered Oak would turn yellow over time if you use it. We used to recoat a salon floor regularly. At a seminar I asked an expert if he had any recommendations for a finish that would wear better than Traffic. He recommended oil poly and said it wears better than any of the top shelf waterborne urethanes, even the one his company sold. Unfortunately the salon was in a residence hotel and we could use it due to the odor. Depending on your wear and tear, Mega HD Clear might be a viable option for you. It costs about $50/gallon less than Traffic.

They told me today that there is a varnish that is transparent. In their opinion, they say it will not yellow and that any yellowing happens after years and years. Not sure if I should just let them do what they are used to doing and not try so hard to look for a water based finish.

None of us have a crystal ball we need pictures and also some info as to what was done .